ARTICLE | doi:10.20944/preprints201903.0269.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: Femtosecond laser; Ultrafast laser; Laser micromachining; Laser drilling; diamond
Online: 28 March 2019 (13:49:58 CET)
A Micro holes in a diamond are presented by using a homemade femtosecond (fs) Yb:KGW laser. An fs laser source was used emitting pulse duration of 230 fs at 1030 nm wavelength, whereas the spot size amounted to 8.9 μm. Parameters like pulse energy, and pulse number were varied over a wide range in order to evaluate their influence both on the micro hole geometry like hole diameter, circularity, taper angle, and on the drilling quality. Hourglass-shaped micro holes whose diameters decrease and increase again after a certain depth have important applications. The results demonstrate the feasibility of extending the drilling of an hourglass-shaped hole in a diamond sample, which has similar diameters at the hole entrance (92 μm) and exit (95 μm), but a much smaller diameter (28 μm) at a certain waist section inside the hole.
ARTICLE | doi:10.20944/preprints201704.0017.v1
Subject: Physical Sciences, Condensed Matter Physics Keywords: ZnO, pulse laser ablation (PLA), laser pulses, laser energy, nanoparticle
Online: 4 April 2017 (09:10:48 CEST)
In this work, zinc oxide (ZnO) thin film has been fabricated on glass substrate using pulse laser ablation (PLA) technique. The effect of laser pulses of 1000, 1500, 2000 pulses at laser energy 700 mJ as well as, laser energy of 600, 700, and 800 mJ at fixed laser pulses of 1500 pulse, with methanol as a solvent on the structural properties of prepared films using XRD, SEM and EDX. XRD results revealed that the ZnO thin films have hexagonal structure with polycrystalline in nature with preferred orientation of (002). Crystalline size was increased with the increasing of the pulses and at energy of 700 mJ and pulse of 1500 pulse seemed nanostructure like tree leaf. In addition, narrow FWHM and no phase change have been observed in all cases. SEM images showed that for all cases the films were homogenous with some island and cluster then cracking started to obtain with the increasing of increase the pulse number. EDX analysis showed that the prepared films were free of defects and contaminations.
ARTICLE | doi:10.20944/preprints201806.0450.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: laser; additive manufacturing; laser beam machining; laser polishing; waviness; roughness; Inconel 718
Online: 27 June 2018 (15:12:32 CEST)
The present work proposes a novel manufacturing technique based on the combination of Laser Metal Deposition, Laser Beam Machining and Laser Polishing processes for the complete manufacturing of complex parts. Therefore, the complete process is based on the application of a laser heat source both for the building of the preform shape of the part by additive manufacturing and for the finishing operations. Their combination enables to manufacture near-net-shape parts and afterwards, remove the excess material via laser machining, which has resulted to be capable of eliminating the waviness resulting from the additive process. Besides, surface quality is improved via laser polishing to reduce the roughness of the final part. Therefore, conventional machining operations are eliminated, what results in a much cleaner process. In order to validate the capability of this new approach, the dimensional accuracy and surface quality of the resulting parts are evaluated. The process has been validated on an Inconel 718 test part, where a previously additively built up part has been finished by means of laser machining and laser polishing.
ARTICLE | doi:10.20944/preprints201702.0094.v1
Subject: Materials Science, General Materials Science Keywords: laser wavelength; polysilicon; laser damage; thermal shock
Online: 27 February 2017 (06:56:01 CET)
Based on PVDF (piezoelectric sensing techniques), this paper attempts to study the propagation law of shock waves in brittle materials during the process of three-wavelength laser irradiation of polysilicon, and discusses the formation mechanism of thermal shock failure. The experimental results show that the vapor pressure effect and the plasma pressure effect in the process of pulsed laser irradiation lead to the splashing of high temperature and high density melt. With the decrease of the laser wavelength, the laser breakdown threshold decreases and the shock wave is weakened. Because of pressure effect of the laser shock, the brittle fracture zone is at the edge of the irradiated area. The surface tension gradient and surface shear wave caused by the surface wave are the result of coherent coupling between optical and thermodynamics. The average propagation velocity of laser shock wave in polysilicon is 8.47×103m/s, and the experiment has reached the conclusion that the laser shock wave pressure peak exponentially distributes attenuation in the polysilicon.
ARTICLE | doi:10.20944/preprints201703.0221.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: Laser triangulation displacement probe; Laser beam pointing; Prism
Online: 30 March 2017 (17:34:55 CEST)
Directional dithering of a laser beam potentially limits the detection accuracy of a laser triangulation displacement probe. A theoretical analysis indicates that the measurement accuracy will linearly decrease as the laser dithering angle increases. To suppress laser dithering, a laser triangulation displacement probe with laser beam pointing control, which consists of a collimated red laser, a laser beam pointing control setup, a receiver lens, and a charge-coupled device, is proposed in this paper. The laser beam pointing control setup is inserted into the source laser beam and the measured object and can separate the source laser beam into two symmetrical laser beams. Hence, at the angle at which the source laser beam dithers, the positional averages of the two laser spots are equal and opposite. Moreover, a laser dithering compensation algorithm is used to maintain a stable average of the positions of the two spots on the imaging side. Experimental results indicate that with laser beam pointing control, the standard variance of the fitting error decreases from 0.3531 to 0.0100, the repeatability accuracy can be decreased from ±7mm to ±5 μm, and the nonlinear error can be reduced from ±6 %FS to ±0.16 %FS.
ARTICLE | doi:10.20944/preprints202201.0204.v1
Subject: Physical Sciences, Fluids & Plasmas Keywords: De Laval nozzle; femtosecond laser micromachining; ultrafast laser sources.
Online: 14 January 2022 (11:24:56 CET)
We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation leads to plasma excitation with a characteristic spectral line emission at 391 nm. By following the emitted signal with a detection system based on an Intensified Charge-Coupled Device (ICCD) we captured the two-dimensional spatial evolution of the photo-excited nitrogen ions with a temporal resolution on the nanosecond time scale. We fabricated the micronozzle on fused silica substrate by femtosecond laser micromachining. This technique enables high accuracy and three-dimensional capabilities, thus providing an ideal platform for developing glass-based microfluidic structures for application to plasma physics and ultrafast spectroscopy.
ARTICLE | doi:10.20944/preprints201801.0052.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: interconnection; multi-layer patterning; laser sintering; femtosecond laser ablation
Online: 8 January 2018 (09:04:08 CET)
The development of printing technologies has enabled the realization of electric circuit fabrication on flexible substrate. However, the current technique remains restricted to single-layer patterning. In this paper, we demonstrate a fully solution-processable patterning approach for multi-layer circuits using a combined method of laser sintering and ablation. Selective laser sintering of silver (Ag) nanoparticle-based ink is applied to make conductive patterns on a heat-sensitive substrate and insulating layer. The laser beam path and irradiation fluence are controlled to create circuit patterns for flexible electronics. Microvia drilling using femtosecond laser through the polyvinylphenol-film insulating layer by laser ablation, as well as sequential coating of Ag ink and laser sintering, achieves an interlayer interconnection between multi-layer circuits. The dimension of microvia is determined by a sophisticated adjustment of laser focal position and intensity. Based on these methods, the flexible electronic circuit with chip-size-package light-emitting diodes was successfully fabricated and demonstrated with functional operations.
ARTICLE | doi:10.20944/preprints201710.0119.v2
Subject: Engineering, Civil Engineering Keywords: laser pointer; displacement monitoring; laser fingerprint; video; data synchronization
Online: 11 December 2017 (15:16:12 CET)
Deck inclination and vertical displacements are among the most important technical parameters to evaluate the health status of a bridge and to verify its bearing capacity. Several methods, both conventional and innovative, are used for structural rotations and displacement monitoring; no one of these does allow, at the same time, precision, automation, static and dynamic monitoring without using high cost instrumentation. The proposed system uses a common laser pointer and image processing. The elastic line inclination is measured by analyzing the single frames of a HD video of the laser beam imprint projected on a flat target. For the image processing, a code was developed in Matlab® that provides instantaneous rotation and displacement of a bridge, charged by a mobile load. An important feature is the synchronization of the load positioning, obtained by a GNSS receiver or by a video. After the calibration procedures, a test was carried out during the movements of a heavy truck maneuvering on a bridge. Data acquisition synchronization allowed to relate the position of the truck on the deck to inclination and displacements. The inclination of elastic line was obtained with a precision of 0.01 mrad. The results demonstrate the suitability of the method for dynamic load tests, control and monitoring of bridges.
ARTICLE | doi:10.20944/preprints202204.0023.v1
Subject: Physical Sciences, Applied Physics Keywords: Ti:sapphire laser; amplifier; injection-lock; Diode pumping; solid state laser
Online: 5 April 2022 (09:51:04 CEST)
A wide variety of applications require high peak laser intensity in conjunction with a narrow spectral linewidth. Typically, injection-locked amplifiers have been employed for this purpose, where a continuous wave oscillator is amplified in a secondary external resonant amplifier cavity using a pulsed pump laser. In contrast, here we demonstrate a setup that combines a CW Ti:sapphire oscillator and pulsed amplifier in a single optical cavity, resulting in a compact system. Dichroic beam combination of blue wavelength semiconductor diodes and the green wavelength of a Nd:YAG laser allowed the simultaneous excitation of the Ti:sapphire crystal by both continuous-wave and pulsed pump sources. A linewidth of <2MHz is achieved in continuous wave operation, while the linewidth increases to about 10MHz in the combined CW + pulsed mode with a pulse duration of 73ns. A peak pulse intensity of 0.2kW is achieved, which should enable efficient single-pass second harmonic generation in a nonlinear crystal.
ARTICLE | doi:10.20944/preprints201910.0052.v1
Online: 4 October 2019 (11:56:36 CEST)
Direct laser writing based on non-linear 3D nanolithography (also known as 3D laser lithography, 3DLL) is a powerful technology to manufacture polymeric micro-optical components. However, practical applications of these elements are limited due to the lack of knowledge of their optical resilience and durability. In this work, we employ 3DLL for the fabrication of bulk (i.e. fully filled) and woodpile structures out of different photopolymers. We then characterize them using S-on-1 laser induced damage threshold (LIDT) measurements. In this way, quantitative data of LIDT values can be collected. Furthermore, this method permits to gather damage morphologies. The results presented in this work demonstrate that LIDT values depend on the material and the geometry of the structure. Bulk non-photosensitized hybrid organic-inorganic photopolymer SZ2080 structures are found to be the most resilient with a damage threshold being of 169±15 mJ/cm2.
ARTICLE | doi:10.20944/preprints201710.0003.v1
Subject: Materials Science, General Materials Science Keywords: selective laser sintering (SLS); porous ceramic; carbon additive; laser absorptivity
Online: 1 October 2017 (06:20:03 CEST)
The aim of this study was to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitation of high melting point, brittleness and low thermal shock resistance from instinct ceramic material properties, the key hurdle lies on very poor absorptivity of oxide ceramics to fiber laser which is widely installed in the commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions was presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser will be discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized.
ARTICLE | doi:10.20944/preprints202105.0114.v1
Subject: Mathematics & Computer Science, Algebra & Number Theory Keywords: selective laser melting; maraging steel, laser power; temperature field; numerical simulation
Online: 6 May 2021 (16:29:46 CEST)
The energy transfer process of laser selective melting is very complex. To study the effect of la-ser selective melting on the microstructure and properties of 18Ni-300 martensitic steel, ABAQUS was used to simulate the temperature of laser cladding 18Ni-300 martensitic steel at different time points and different laser power. The results show that the cross-section shape of the molten pool changes from round to oval With the increase of laser power, the higher the peak value of temperature time curve, the greater the temperature gradient; and the laser clad-ding experiment of 18Ni-300 martensitic steel was carried out, and the microstructure and me-chanical properties of the samples under different laser power were analyzed. The results show that with the increase of laser power, the grain size of the cladding layer becomes smaller and the microstructure becomes more compact; the hardness of the side surface of the sample is higher than that of the upper surface, and the tensile strength and elongation show a trend of first increasing and then decreasing.
ARTICLE | doi:10.20944/preprints201801.0263.v1
Online: 28 January 2018 (16:54:46 CET)
An important surgical goal is to provide a first intention wound healing without trauma produced by sutures and for this aim in the past several methods have been tested. The aim of this preliminary ex vivo study is to demonstrate the capacity of a 1070 nm pulsed fiber laser to treat the dental fractures by dentine melting with the apposition of hydroxyapatite nanoparticles as filler. Only the specimens of the group b showed a real process of welding of the two parts, while specimens of groups a and c did not reach a complete welding process. Out of thirty freshly-extracted human third molars, decay-free, twenty-four cylinders of 5 mm thickness were obtained to perform the test. The device used was a 1070 nm Yb-doped pulsed fiber laser: this source has a maximum average output power of 20 W and a fixed pulse duration of 100 ns, while the repetition rate ranges from 20 kHz to 100 kHz. The samples were divided in three groups (a, b, c) of eight teeth and each specimen, with the two portions strictly placed side by side, was put inside the box and irradiated three times, the first and the second at 30 kW and the last at 10 kW power. The frequency was maintained at 20 kHz for all the tests as well as the speed of the beam at 10 mm/sec. The samples of the group a were irradiated without apposition, in the group b nanoparticles (<200 nm) of hydroxyapatite were put in the gap between the two portions while in the group c, a powder of hydroxyapatite was employed. Only the specimens of the group b showed a real process of welding of the two parts, while specimens of groups a and c did not reach a complete welding process.
Subject: Physical Sciences, Optics Keywords: tellurite fiber laser; tellurite glass fiber; microlaser; microsphere laser; rare-earth ions
Online: 7 March 2020 (08:41:06 CET)
In recent years, tremendous progress has been made in the development of rare-earth ion doped tellurite glass laser sources, ranging from watt and multiwatt level fiber lasers to nanowatt level microsphere lasers. Significant success has been achieved in extending the spectral range of tellurite fiber lasers generating at wavelengths beyond 2 μm as well as in theoretical understanding. This review is aimed at discussing the state of the art of neodymium-, erbium-, thulium-, and holmium-doped tellurite glass fiber and microsphere lasers.
ARTICLE | doi:10.20944/preprints201611.0001.v1
Subject: Materials Science, Polymers & Plastics Keywords: direct laser writing; ultrafast laser; 3D laser lithography; 3D printing; hybrid polymer; integrated microoptics; optical damage; photonics; pyrolysis; ceramic 3D structures
Online: 1 November 2016 (04:59:50 CET)
We introduce optically clear and resilient free-form micro-optical of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nanooptics, including their integration directly onto optical fibers. A systematic study on the fabrication peculiarities and quality of resultant structures is performed. Comparison of microlenses’ resiliency to CW and femtosecond pulsed exposure is determined. Experimental results prove that pure SZ2080 is ∼3 fold more resistant to high irradiance as compared with a standard photo-sensitized material and can sustain up to 1.91 GW/cm2 intensity. 3DLL is a promising manufacturing approach for high-intensity micro-optics for emerging fields in astro-photonics and atto-second pulse generation. Additionally, pyrolysis is employed to shrink structures up to 40% by removing organic SZ2080 constituents. This opens a promising route towards downscaling photonic lattices and creation of mechanically robust glass-ceramic structures.
REVIEW | doi:10.20944/preprints202010.0292.v1
Subject: Materials Science, Biomaterials Keywords: laser powder bed fusion; Inconel 718; high temperature; material characterisation; laser shock peening
Online: 14 October 2020 (09:11:10 CEST)
This paper reviews state of the art Additive Manufactured (AM) IN718 alloy intended for high temperature applications. AM processes have been around for decades and have gained traction in the past five years due to the huge economic benefit it brings to manufacturers. It is crucial for the scientific community to look into AM IN718 applicability in order to see a step-change in the production. Microstructural studies reveal that the grain structure plays a significant role in determining the fatigue lifespan of the material. Controlling IN718 respective phases such as the ϒ’', δ and Laves phase is seen to be crucial. Literature reviews have shown that the mechanical properties of AM IN718 were very close to its wrought counterpart when treated appropriately. Higher homogenization temperature and longer ageing were recommended to dissolve the damaging phases. Various surface enhancement techniques were examined to find out their compatibility to AM IN718 alloy that is intended for high temperature application. Laser shock peening (LSP) technology stands out due to the ability to impart low cold work which helps in containing the beneficial compressive residual stress it brings in high temperature fatigue environment.
ARTICLE | doi:10.20944/preprints202001.0351.v1
Subject: Physical Sciences, Optics Keywords: Optical biopsy; Raman spectroscopy; Micro-optics; Ultrafast laser assisted etching; Femtosecond laser micromaching
Online: 29 January 2020 (10:38:18 CET)
Optical biopsy describes a range of medical procedures in which light is used to investigate disease in the body, often in hard-to-reach regions via optical fibres. Optical biopsies can reveal a multitude of diagnostic information to aid therapeutic diagnosis and treatment with higher specificity and shorter delay than traditional surgical techniques. One specific type of optical biopsy relies on Raman spectroscopy to differentiate tissue types at the molecular level and has been used successfully to stage cancer. However, complex micro-optical systems are usually needed at the distal-end to optimise the signal-to-noise properties of the Raman signal collected. Manufacturing these devices remains a critical challenge, particularly in a way suitable for large scale adoption. In this paper, we describe a novel fibre-fed micro-optic system designed for efficient signal delivery and collection during a Raman spectroscopy based optical biopsy. Crucially, we fabricate the device using a direct-laser-writing technique known as ultrafast laser assisted etching which is scalable and allows components to be aligned passively. The Raman probe has a sub-millimetre diameter and offers confocal signal collection with 71.3 ± 1.5% collection efficiency over a 0.8 numerical aperture. Proof of concept spectral measurements were performed on mouse intestinal tissue and compared with results obtained using a commercial Raman microscope.
ARTICLE | doi:10.20944/preprints201911.0028.v1
Subject: Chemistry, Analytical Chemistry Keywords: gas sensor; hydrogen sensor; diode laser; TDLAS; WMS; absorption spectroscopy; laser spectroscopy; hydrogen
Online: 3 November 2019 (18:21:16 CET)
A laser-based hydrogen (H2) sensor using wavelength modulation spectroscopy (WMS) was developed for contactless measurements of molecular hydrogen. The sensor uses a distributed feedback (DFB) laser to target the H2 quadrupole absorption line at 2121.8 nm. The H2 absorption line exhibits weak collisional broadening and strong collisional narrowing effects. Both effects were investigated by comparing measurements of the absorption linewidth with detailed models using different line profiles that include collisional narrowing effects. The collisional broadening and narrowing parameters were determined for pure hydrogen as well as for hydrogen in nitrogen and air. Performance of the sensor was evaluated and the sensor applicability for H2 measurements in a range of 0- 10 %v of H2 was demonstrated. A precision of 0.02 %v was achieved with 1 meter of absorption pathlength (0.02 %v∙m) and 1 s of integration time. For the optimum averaging time of 20 s a precision of 0.005 %v∙m was achieved. A good linear relationship between H2 concentration and the sensor response was observed. A simple and robust transmitter-receiver configuration of the sensor allows in-situ installations in harsh industrial environments.
ARTICLE | doi:10.20944/preprints201811.0428.v1
Subject: Materials Science, General Materials Science Keywords: K417G Ni-based superalloy; laser forming repairing; laser remelting; microstructure; cracking behavior; tribology
Online: 19 November 2018 (07:17:23 CET)
K417G Ni-based superalloy is widely used in aeroengine turbine blade for its excellent properties. However, the aeroengine rotor blade zigzag crown appears early failure frequently, which is because of the wear problems occurring in the working process. Laser forming repairing (LFR) is a promising technique to repair these damaged blades. Unfortunately, the laser formed Ni-based superalloys with high content of (Al + Ti) have a high cracking sensitivity. In this paper, the crack characterization of the LFRed K417G, the microstructure, microhardness and tribological properties of the coating before and after laser remelting are presented. The results show that the microstructure of as-deposited K417G consists of γ phase, γ′ precipitated phase, γ + γ′ eutectic and carbide. Cracking mechanisms including solidification cracking, liquation cracking and ductility dip cracking are proposed based on the composition of K417G and processing characteristics to explain the cracking behavior of the K417G superalloy during LFR. After laser remelting, the microstructure of the coating has been refined, and the microhardness and tribological properties has been improved. Laser remelting can decrease the size of the cracks in the LFRed K417G but not the number. Therefore, laser remelting can be applied as an effective method for strengthening coating and as an auxiliary method for controlling cracking.
ARTICLE | doi:10.20944/preprints202203.0204.v1
Online: 15 March 2022 (10:46:57 CET)
To increase the network computer and mobile telephone capacity one needs a laser to carry information instead of electrons. Since the laser is very fast compared to electrons, one expects information to be transmitted very fast through the network (internet). This requires searching for chips that act as capacitors, inductors, or evens as resistors this work shows that the laser traveling beam diminished as the frequency reciprocal thus acts as a capacitor or diminished as frequency thus acts as an inductor and sometimes diminished with the concentration of carriers thus act as a resistor for magnetic materials with strength that cancels the friction force when the laser frequency is equal nearly to the atoms natural frequency the material act as an inductor. Then frictional force is dominant with high mobility dielectric, the material acts as a capacitor. However, it acts as a conductor for negligible friction and natural frequency.
ARTICLE | doi:10.20944/preprints202112.0105.v1
Subject: Materials Science, Surfaces, Coatings & Films Keywords: Diamond; Magnetic order; Laser treatment
Online: 7 December 2021 (13:32:45 CET)
In this work, we demonstrate that cutting diamond crystals with a laser (532 nm wavelength, 0.5 mJ energy, 200 ns pulse duration at 15 kHz) produces a ≲20nm thick surface layer with magnetic order at room temperature. We have measured the magnetic moment with a SQUID magnetometer of six natural and six CVD diamond crystals of different size, nitrogen content and surface orientations. A robust ferromagnetic response at 300 K is observed only for crystals that were cut with the laser along the (100) surface orientation. The magnetic signals are much weaker for the (110) and negligible for the (111) orientations. We attribute the magnetic order to the disordered graphite layer produced by the laser at the diamond surface. The ferromagnetic signal vanished after chemical etching or after moderate temperature annealing. The obtained results indicate that laser treatment of diamond may pave the way to create ferromagnetic spots at its surface.
ARTICLE | doi:10.20944/preprints202107.0529.v1
Online: 23 July 2021 (08:10:44 CEST)
Inflammation of the periodontal tissue (periodontitis) is the highest problem of oral health in Indonesia after caries. Photoacoustic imaging (PAI) is a new imaging technique that can be simply constructed using a diode laser combined with a condenser microphone. This study aims to determine that a simple PAI system was able to image periodontal disease in animal model. Samples of the study were normal periodontal and periodontitis tissue, obtained from Sprague-Dawley rats that were divided into four groups, i.e. the control group, treatment group 1 (7 days periodontitis induction), treatment group 2 (11 days periodontitis induction), and treatment group 3 (14 days periodontitis induction). The PAI system was controlled by Labview and Arduino IDE software from a personal computer. Results of the study reveal that the optimal frequency of laser modulation for periodontal tissue imaging was 19 kHz with duty cycle of 50%. Photoacoustic (PA) intensity was obtained from higher to lower of -68,71 dB (treatment group 3), -70,69 dB (treatment group 2), -71,69 dB (treatment group 1), and -73,07 dB (control group) respectively. The photoacoustic images were analyzed to define the contrast between sample and media. The PA intensity of the samples were higher than media. Therefore, this study demonstrate the feasibility of simple PAI system to differentiate normal periodontal tissue and periodontitis.
ARTICLE | doi:10.20944/preprints202002.0287.v1
Subject: Materials Science, Biomaterials Keywords: Ag; Colletotrichum gloeosporioides; laser; dewetting
Online: 20 February 2020 (06:53:09 CET)
Silver particles are prepared by dewetting Ag ﬁlms coated on glass using a fiber laser. The size of the particles is controlled in the range of 92 nm ~ 1.2 μm by adjusting the thickness of the Ag film. The structural properties and surface roughness of the particles are evaluated by means of scanning electron microscopy. In addition, the antifungal activity of the Ag particles is examined using spore suspensions of Colletotrichum gloeosporioides. It is shown that the particles with a size of 1.2 μm achieve 100% inhibition of the conidia growth of the Colletotrichum gloeosporioides after a contact time of just 5 min. Furthermore, the smaller particles also achieve a good antibacterial activity given a longer contact time. Similar results are observed in spore germination and pathogenicity tests performed on mango fruit and leaves. Overall, the results confirm that the Ag particles have an excellent antifungal effect on Colletotrichum gloeosporioides.
Subject: Materials Science, Nanotechnology Keywords: femtosecond laser; birefringence; stress; sapphire
Online: 23 August 2019 (09:49:21 CEST)
Birefringence of 3 × 10-3 is demonstrated inside cross-sectional regions of 100 µm, inscribed by axially stretched Bessel-beam-like fs-laser pulses along the c-axis inside sapphire. A high birefringence and retardance of λ/4 at mid-visible spectral range (green) can be achieved utilizing stretched beams with an axial extension of 30-40 µm. Conditions of laser writing chosen ensure that there are no formations of self-organised nano-gratings. This method can be adopted for the creation of polarisation optical elements and fabrication of spatially varying birefringent patterns for optical vortex generation.
ARTICLE | doi:10.20944/preprints202011.0429.v1
Subject: Materials Science, Biomaterials Keywords: laser ablation; noble-metal films; magnetron sputtering; nanosecond laser pulses; porous nanostructures; plasmonics; nanosponges
Online: 16 November 2020 (15:27:14 CET)
Three-dimensional porous nanostructures made of noble metals represent novel class of nanomaterials promising for nonlinear nanooptics and sensors. Such nanostructures are typically fabricated using either reproducible yet time-consuming and costly multi-step lithography protocols or less reproducible chemical synthesis that involve liquid processing with toxic compounds. Here, we combined scalable nanosecond-laser ablation with advanced engineering of the chemical composition of thin substrate-supported Au films to produce nanobumps containing multiple nanopores inside. Most of the nanopores hidden beneath the nanobump surface can be further uncapped using gentle etching of the nanobumps by an Ar-ion beam to form functional 3D plasmonic nanosponges. The nanopores 10-150~nm in diameter were found to appear via laser-induced explosive evaporation/boiling and coalescence of the randomly arranged nucleation sites formed by nitrogen-rich areas of the Au films. Density of the nanopores can be controlled by the amount of the nitrogen in the Au films regulated in the process of their magnetron sputtering assisted with nitrogen-containing discharge gas.
ARTICLE | doi:10.20944/preprints202010.0619.v1
Subject: Materials Science, Surfaces, Coatings & Films Keywords: amorphous silicon; polycrystalline silicon; thin films; laser-induced annealing; femtosecond laser pulses; Raman spectroscopy
Online: 29 October 2020 (14:44:58 CET)
Amorphous silicon (α-Si) film present an inexpensive and promising material for optoelectronic and nanophotonic applications. Its basic optical and optoelectronic properties are known to be improved via phase transition from amorphous to polycrystalline phase. Infrared femtosecond laser radiation can be considered as a promising nondestructive and facile way to drive uniform in-depth and lateral crystallization of α-Si films that are typically opaque in UV-visible spectral range. However, so far only a few studies reported on utilization of near-IR radiation for laser-induced crystallization of α-Si providing no information regarding optical properties of the resultant polycrystalline Si films. The present work demonstrates efficient and gentle single-pass crystallization of α-Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of laser-annealed films by atomic-force microscopy, optical, micro-Raman and energy-dispersive X-ray spectroscopy, as well as numerical modeling of optical spectra, confirmed efficient crystallization of α-Si and high-quality of the obtained films. Moreover, we highlight localized laser-driven crystallization of α-Si as a promising way for optical information encryption, anti-counterfeiting and fabrication of micro-optical elements.
ARTICLE | doi:10.20944/preprints201809.0273.v1
Subject: Medicine & Pharmacology, Dentistry Keywords: Low level laser therapy; diode laser; Orthodontic tooth movement; Pain; Split-mouth clinical trial
Online: 15 September 2018 (18:18:29 CEST)
This study evaluated the effect of low-level laser irradiation induces by diode laser on the speed of orthodontic tooth movement of canines submitted to initial retraction. Twenty-four mandibular canines were retracted by using NiTi spring (force of 150 g/side). Thirteen of those were irradiated with a diode laser 980-nm diode laser (Wiser Laser Doctor Smile, Lambda) operating at an 810-nm wavelength (1 W of output power, continuous wave of 66.7 J/cm2) that was equipped with a 0.6-mm optical fiber in continuous-wave mode. The canine retraction was accomplished by using prefabricated coil springs. The right of the mandible was chosen to be irradiated with the laser, whereas the left side was considered the control without laser irradiation. The laser was applied with 0-, 3-, 7-, and 14-day intervals. The amount of canine retraction was measured with a digital electronic caliper while the pain level was prompted by a patient questionnaire. The speed of tooth movement was significantly greater in the laser group than in the control group. The pain intensity was also at a lower level in the laser group. Our findings suggest that diode laser therapy can highly accelerate tooth movement during orthodontic treatment and can also effectively reduce pain level.
ARTICLE | doi:10.20944/preprints201807.0319.v1
Subject: Physical Sciences, Applied Physics Keywords: laser-induced breakdown spectroscopy; atomic spectroscopy; plasma spectroscopy; laser spectroscopy; physical properties of biomaterials
Online: 18 July 2018 (08:34:46 CEST)
This work reports measurements of calcified gallstone elemental compositions using laser-induced optical emission spectroscopy. The experimental results support the importance of the magnesium concentration in gallstone growth. Granular stones reveal an increased magnesium concentration at the periphery of the granules, suggesting the inhibition of further growth. Non-granular gallstones reveal lower overall magnesium concentrations but with higher values near the center.
ARTICLE | doi:10.20944/preprints202110.0366.v1
Subject: Materials Science, Nanotechnology Keywords: Magnesium nanoparticles; Laser scan speed, Wearables; Pulsed Laser Ablation in Liquid; Advanced manufacturing; Flexile sensors; Powder metallurgy; Surface science; Nanoparticle size distributions; Picosecond laser
Online: 25 October 2021 (15:46:16 CEST)
Magnesium nanoparticles of various mean diameters (53 – 239 nm) were synthesized herein via Pulsed Laser Ablation in Liquid (PLAL) from millimeter sized magnesium powders within iso-propyl alcohol. It was observed via a 3x3 full factorial DOE that the processing parameters can control the nanoparticle distribution to produce three size-distribution types (bimodal, skewed and normal). Ablation times of 2, 5, and 25 minutes where investigated. An ablation time of 2 minutes produced a bimodal distribution with the other types seen at higher periods of processing. Mg nanoparticle UV-Vis absorbance at 204 nm increased linearly with increasing ablation time, indicating an increase in nanoparticle count. The colloidal density (mg/ml) generally increased with increasing nanoparticle mean diameter as noted via increasing UV-vis absorbance. High la-ser scan speeds (within the studied range of 3000 - 3500 mm/s) tend to increase the nanoparticle count/yield. For the first time, the effect of scan speed on colloidal density, UV-vis absorbance and nanoparticle diameter from metallic powder ablation was investigated and is reported herein. The nanoparticles formed dendritic structures after being drop cast on aluminum foil as observed via FESEM analysis. Dynamic light scattering was used to measure the size of the nanoparticles. Magnesium nanoparticles have promising use in the fabrication of wearables, such as in conductive tracks or battery electrodes, owing to their low heat capacity, high melting point and bio-compatibility.
COMMUNICATION | doi:10.20944/preprints202203.0033.v1
Subject: Physical Sciences, Optics Keywords: laser remote sensing; photon-counting lidar; microchip laser; passively Q-switching; compact solid-state lasers
Online: 2 March 2022 (06:53:36 CET)
As a critical transmitter, the compact 532 nm lasers operating on high repetition and narrow pulse widths have been used widely for airborne or space-borne laser active remote sensing. We developed a free space pumped TEM00 mode sub-nanosecond 532 nm laser that occupied a volume of less than 125 mm × 50 mm × 40 mm (0.25 liters). The fundamental 1064 nm laser consists of a passively Q-switched composite crystal microchip laser and an off-axis, two-pass power amplifier. The pump sources were two single-emitter semiconductor laser diodes (LD) of 808 nm with a maximum continuous wave (CW) power of 10 W each. The average power of fundamental 1064 nm laser was 1.26 W with the laser operating at 16 kHz repetition rates, and 857ps pulse widths. Since the beam distortion would be severe in microchip lasers in terms of the increase in heat load, for obtaining a high beam quality of 532 nm, the beam distortion was compensated by adjusting the distribution of pumping beam in our experiment of fundamental amplification. Furthermore, better than 0.6 W average power, 770 ps, beam quality of M2 ＜1.2, and 16 kHz pulse output at 532 nm was obtained by a Type I LiB3O5 (LBO) crystal in the critical phase matching (CPM) regime for second harmonic generation (SHG).
ARTICLE | doi:10.20944/preprints201912.0022.v1
Subject: Physical Sciences, Optics Keywords: direct laser processing; femtosecond laser pulses; superhydrophobic textures; analyte enrichment; plasmonic nanostructures; SERS; medical drugs
Online: 3 December 2019 (11:19:55 CET)
We report an easy-to-implement device for SERS-based detection of various analytes dissolved in water droplets at trace concentrations. The device combines an analyte-enrichment system and SERS-active sensor site, both produced via inexpensive and high-performance direct fs-laser printing. Fabricated on a surface of water-repellent polytetrafluoroethylene substrate as an arrangement of micropillars, the analyte-enrichment system supports evaporating water droplet in the Cassie-Baxter superhydrophobic state, thus ensuring delivery of the dissolved analyte molecules towards the hydrophilic SERS-active site. The efficient pre-concentration of the analyte onto the sensor site based on densely-arranged spiky plasmonic nanotextures results in its subsequent label-free identification by means of SERS spectroscopy. Using the proposed device, we demonstrate reliable SERS-based fingerprinting of various analytes, including common organic dyes and medical drugs at ppb concentrations. The proposed device is believed to find applications in various areas, including label-free environmental monitoring, medical diagnostics, and forensics.
ARTICLE | doi:10.20944/preprints202209.0448.v1
Online: 29 September 2022 (03:27:46 CEST)
Deposition/printing of materials with sub-1 μm precision and size (cross sections) is required for optical and electrical micro-devices. Crystalline c-ITO (Indium tin oxide) nanostructures were patterned on glass with a precision that formed gaps of 20-50 nm between individual disks or lines of ∼ 250 nm diameter or width. The absorbed energy density [J/cm3] followed the second order dependence on pulse energy. This facilitated high resolution and precision for nanoscale laser writing at the 515 nm laser wavelength. Patterns for optical elements such as circular gratings and micro-disks were laser printed using ITO as a resist. Unexposed amorphous a-ITO was chemically removed in aqueous 1% vol. HF solution. This use of a-ITO as solid-resist is promising for metamaterial and micro-optical applications.
Subject: Physical Sciences, Acoustics Keywords: laser interferometry; displacement sensing; ghost beams
Online: 5 March 2021 (11:13:44 CET)
We present a compact optical head design for wide-range and low noise displacement sensing using deep frequency modulation interferometry. The on-axis beam topology is realised in a quasi-monolithic component and relies on cube beamsplitters and beam transmission through perpendicular surfaces to keep angular alignment constant when operating in air or vacuum, which leads to the generation of ghost beams that can limit the phase readout linearity. We investigate the coupling of these beams into the non-linear phase readout scheme of DFMI and demonstrate adjustments of the phase estimation algorithm to reduce this effect. This is done through a combination of balanced detection and the inherent orthogonality of beat signals with different relative time-delays in deep frequency modulation interferometry that is a unique feature not available for heterodyne, quadrature or homodyne interferometry.
Subject: Physical Sciences, General & Theoretical Physics Keywords: quantum thermodynamics; laser cooling; cavitation; sonoluminescence
Online: 7 February 2020 (03:13:02 CET)
In this paper, we design a quantum heat exchanger which converts heat into light on relatively short quantum optical time scales. Our scheme takes advantage of collective cavity-mediated laser cooling of an atomic gas inside a cavitating bubble. Laser cooling routinely transfers individually trapped ions to nano-Kelvin temperatures for applications in quantum technology. The quantum heat exchanger which we propose here is expected to provide cooling rates of the order of Kelvin temperatures per millisecond and is expected to find applications in micro and nanotechnology.
ARTICLE | doi:10.20944/preprints201909.0030.v1
Subject: Physical Sciences, Optics Keywords: ablation; magnetic field; femtosecond laser fabrication
Online: 3 September 2019 (05:24:27 CEST)
Laser ablation of silicon under an external applied magnetic field with different orientations was investigated in respect to the scanning direction and polarisation of the laser beam, by observation of the ablation patterns and debris deposition. Ultra-short ∼230 fs laser pulses of 1030 nm wavelengths were used in the single and multi-pulse irradiation modes. Ablation with an externally applied magnetic B-field (B ≈ 0.1 T) is shown to strongly affect debris formation. The mechanism of surface plasmon polariton (SPP) wave can explain the ablated periodic patterns observed with alignment along the magnetic field lines.
Online: 25 April 2019 (15:09:38 CEST)
The subject of the research is to Development of laser ablation method for Fabrication of surface acoustic wave sensors on quartz wafer, the target of the GQW – is to design Acoustic wave sensor by using laser ablation method. By using the surface acoustic wave theory to sense by the signal and using this physical phenomenon, We will design the sensor which transduce an input electrical signal into a mechanical wave which unlike an electrical signal, can be easily influenced by physical phenomena. The device then transducers this wave back into an electrical signal on the secondary terminal of the sensor. Changes in amplitude, phase, frequency, or time-delay between the input and output electrical signals can be used to measure the presence of the desired Our work in this part, especially the practical part like temperature, vibration ,etc. we design a combs on the waver of quartz to make like an electrode primary electrode & secondary electrode by putting coats of cuppers & vanadium on the waver and then using the fiber optic laser regime to design this combs to can able transfer the signal by ablation the most important here to use the regime of fiber optic laser then we using this sensor in any electronic circuit How we will select the suitable kind of laser to design, this is the most important part, and what it will be the diameter of that combs of secondary and primary , how much the value of the wave length to select the micro distant combs to avoid any inductance and interference for transferred signal , also take the benefit of using MEMS theory in our project.
ARTICLE | doi:10.20944/preprints201706.0023.v1
Online: 5 June 2017 (05:18:53 CEST)
The deformation of underground gateroads tends to be asymmetric and complex. Traditional instrumentation fails to accurately and conveniently monitor the full cross-sectional deformation of underground gateroads. Here, a full cross-sectional laser scanner was developed together with a visualization software package. The developed system used polar coordinate measuring method and the full cross-sectional measurement was realized by 360° rotation of laser sensor driven by an electrical motor. Later on, the potential impact of gateroad wall flatness, roughness and geometrical profile as well as coal dust environment on the performance of the developed laser scanner were evaluated. The studies show that a high-level flatness is favorable in application of the developed full cross-sectional deformation monitoring system. For a smooth surface of gateroad, the sensor cannot receive reflected light when the incidence angle of laser beam is large, causing data loss. Conversely, the roughness surface shows its priority as the diffuse reflection light can be received by the sensor. With regards to the coal dust in measurement environment, the fine particles of floating coal dust in the air can lead to the loss of measurement data to some certain due to scattering of laser beam.
ARTICLE | doi:10.20944/preprints201703.0178.v1
Subject: Earth Sciences, Geoinformatics Keywords: mobile laser scanning; voxel; clustering; segmentation
Online: 23 March 2017 (08:48:22 CET)
The segmentation of urban scene mobile laser scanning (MLS) data into meaningful street objects is a great challenge due to the scene complexity of street environments, especially in the vicinity of street objects such as poles and trees. This paper proposes a three-stage method for the segmentation of urban MLS data at the object level. The original unorganized point cloud is first voxelized, and all information needed is stored in the voxels. These voxels are then classified as ground and non-ground voxels. In the second stage, the whole scene is segmented into clusters by applying a density-based clustering method based on two key parameters: local density and minimum distance. In the third stage, a merging step and a re-assignment processing step are applied to address the over-segmentation problem and noise points, respectively. We tested the effectiveness of the proposed methods on two urban MLS datasets. The overall accuracies of the segmentation results for the two test sites are 98.3% and 97%, thereby validating the effectiveness of the proposed method.
ARTICLE | doi:10.20944/preprints201609.0020.v1
Online: 6 September 2016 (11:51:45 CEST)
A portable laser photoacoustic sensor based on a Field-Programmable Gate Array (FPGA) is reported for methane detection. A tunable DFB diode laser in the 1654 nm wavelength range is used as an excitation source. The photoacoustic signal processing was implemented by a FPGA device. A small resonant photoacoustic cell is designed. The minimum detection limit (1σ) of 10 ppm for methane (CH4) is demonstrated.
ARTICLE | doi:10.20944/preprints202108.0443.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: Laser welding; Cu-Al welding; green laser; Micro-structure analysis; Energy dispersive X-ray spectroscopy (EDS))
Online: 23 August 2021 (13:28:28 CEST)
In laser joining of copper (Cu) and aluminum (Al) sheets, the Al sheet is widely chosen as the top surface for laser irradiation because of increased absorption of laser beam and lower melting temperature of Al in contrast to Cu. This research focus on welding from Cu side to Al sheet. The main objective of irradiating the laser beam from the copper side (Cu on top) is to exploit higher solubility of Al in Cu. A significantly lower laser power can be used with 515 nm laser in comparison to 1030 nm. In addition to low laser power, a stable welding is obtained with 515 nm. Because of this advantage, 515 nm is selected for the current research. By fusion of Cu and Al the two sheet metals are welded, with presence of beneficial Cu solid solution phase and Al+Al2Cu in the joint with the brittle phases intermixed between the ductile phase. Therefore the mixed composition strengthens the joint. However excessive mixing leads to formation of more detrimental phases and less ductile phases. Therefore optimum mixing must be maintained. Energy dispersive X-ray spectroscopy (EDS) analysis indicate that large amount of beneficial Cu solid solution and Al rich phases is formed in the strong joint. From the tensile shear test for a strong joint, fracture is obtained on the heat-affected zone (HAZ) of Al. Therefore the key for welding from copper side is to have optimum melt with beneficial phases like Cu and Al+ Al2Cu and the detrimental phases intermixed between the ductile phases
ARTICLE | doi:10.20944/preprints201907.0156.v1
Subject: Physical Sciences, Atomic & Molecular Physics Keywords: molecular spectroscopy; diatomic spectroscopy; Abel transform; plasma spectroscopy; laser-induced breakdown spectroscopy; laser-induced plasma; plasma dynamics
Online: 11 July 2019 (09:30:23 CEST)
Spatially resolved, line-of-sight measurements of aluminum monoxide emission spectra in laser ablation plasma are used with Abel inversion techniques to extract radial plasma temperatures. Contour mapping of the radially deconvolved signal intensity shows a ring of AlO formation near the plasma boundary with the ambient atmosphere. Simulations of the molecular spectra were coupled with the line profile fitting routines. Temperature results are presented with simultaneous inferences from lateral, asymmetric radial, and symmetric radial AlO spectral intensity profiles. This analysis indicates that we measured shockwave phenomena in the radial profiles, including a temperature drop behind the blast wave created during plasma initiation.
REVIEW | doi:10.20944/preprints201805.0459.v1
Subject: Physical Sciences, Astronomy & Astrophysics Keywords: white dwarfs; burning in stars; plasma diagnostics; atomic spectra; plasma spectroscopy; laser spectroscopy; laser-induced breakdown spectroscopy
Online: 31 May 2018 (05:13:00 CEST)
This work communicates a review on Balmer series hydrogen beta line measurements and applications for analysis of white dwarf stars. Laser-induced plasma investigations explore electron density and temperature ranges comparable to white dwarf star signatures such as Sirius B, the companion to the brightest star observable from the earth. Spectral line shape characteristics of the hydrogen beta line include width, peak separation, and central dip-shift, thereby providing three indicators for electron density measurements. The hydrogen alpha line shows two primary line-profile parameters for electron density determination, namely, width and shift. Both Boltzmann plot and line-to-continuum ratios yield temperature. The line-shifts recorded with temporally- and spatially- resolved optical emission spectroscopy of hydrogen plasma in laboratory settings can be larger than gravitational redshifts that occur in absorption spectra from radiating white dwarfs. Published astrophysical spectra display significantly diminished Stark or pressure broadening contributions to red-shifted atomic lines. Gravitational redshifts allow one to assess the ratio of mass and radius of these stars, and subsequently, the mass from cooling models.
ARTICLE | doi:10.20944/preprints202208.0240.v1
Subject: Physical Sciences, Nuclear & High Energy Physics Keywords: polarized ion beam; polarimetry; laser-plasma acceleration
Online: 12 August 2022 (12:51:46 CEST)
We present a compact polarimeter for 3He ions with special emphasis on the analysis of short-pulsed beams accelerated during laser-plasma interactions. We discuss the specific boundary conditions for the polarimeter, such as the properties of laser-driven ion beams, the selection of the polarization-sensitive reaction in the polarimeter, the representation of the analyzing-power contour map, the choice of the detector material used for particle identification, as well as the production procedure of the required deuterated foil-targets. The assembled polarimeter has been tested using a tandem accelerator delivering unpolarized 3He ion beams, demonstrating good performance in the few-MeV range. The statistical accuracy and the deduced figure-of-merit of the polarimetry are discussed, including the count-rate requirement and the lower limit of accuracy for beam-polarization measurements at a laser-based ion source.
ARTICLE | doi:10.20944/preprints202111.0563.v1
Subject: Physical Sciences, Optics Keywords: Laser induces damage threshold; ZnGeP2; Magnetorheological polish
Online: 30 November 2021 (11:50:44 CET)
Magnetorheological processing was applied to polish the working surfaces of the ZnGeP2 single crystal, in which a non-aqueous liquid with magnetic particles of carbonyl iron with the addition of nanodiamonds was used. Samples of a single crystal ZnGeP2 with an angstrom level of surface roughness were received. the use of MRP has allowed more accurately characterizing possible structural defects that have emerged on the surface of a single crystal and have a size of ~ 0.5-1.5 μm. the LIDT value at the indicated or-ders of magnitude of the surface roughness parameters is determined not by the quality of polishing, but by the number of point depressions caused by physical limitations of the structural configuration of the crystal volume. These results are in good agreement with the assumption made about a significant effect of the concentration of dislocations in a ZnGeP2 crystal on LIDT.
ARTICLE | doi:10.20944/preprints202012.0333.v1
Subject: Earth Sciences, Atmospheric Science Keywords: LIDAR; UV laser; high spectral resolution; aerosols
Online: 14 December 2020 (13:11:08 CET)
ATLID (ATmospheric LIDar) is the atmospheric backscatter LIDAR (Light Detection and Ranging) on board of the EarthCARE (Earth Cloud, Aerosol and Radiation Explorer) mission, the sixth Earth Explorer Mission of the ESA (European Space Agency) Living Planet Programme [1-5]. ATLID’s purpose is to provide vertical profiles of optically thin cloud and aerosol layers, as well as the altitude of cloud boundaries [6-10]. In order to achieve this objective ATLID emits short duration laser pulses in the UV, at a repetition rate of 51 Hz, while pointing in a near nadir direction along track of the satellite trajectory. The atmospheric backscatter signal is then collected by its 620 mm aperture telescope, filtered through the optics of the instrument focal plane assembly, in order to separate and measure the atmospheric Mie and Rayleigh scattering signals. With the completion of the full instrument assembly in 2019, ATLID has been subjected to an ambient performance test campaign, followed by a successful environmental qualification test campaign, including performance calibration and characterization in thermal vacuum conditions. In this paper the design and operational principle of ATLID is recalled and the major performance test results are presented, addressing the main key receiver and emitter characteristics. Finally, the estimated instrument, in-orbit, flight predictions are presented; these indicate compliance of the ALTID instrument performance against its specification and that it will meet its mission science objectives for the EarthCARE mission, to be launched in 2023.
Subject: Engineering, Mechanical Engineering Keywords: titanium; laser marking; color; reflectance; roughness; oxidation
Online: 26 August 2019 (16:15:09 CEST)
Surface treatments of metals based on laser marking technology is an important application in a wide range of industrial fields. By specific combinations of laser processing parameters, the modified surface leads to different textures with specific roughness and colored appearance. Most of current works are focused on the modification of color tonality of flat surfaces, or the development of specific topography features, but the combination of both processes is not usually evaluated, mainly due to the complexity to control the optical properties on rough surfaces. This research presents an analysis of the influence of the micro-geometrical characteristics of periodic patterned laser tracks on the chromaticity and reflectance of Ti6Al4V substrates. The samples were irradiated with an infrared nanosecond pulsed laser under air atmosphere, taking as control parameter the scan speed of the beam. A roughness evaluation, microscopic inspection, absorption and chromaticity examination were conducted. Although micro-crack growth was detected in isolated case (10 mm/s), the possibility of adjusting the result color were demonstrated by controlling the thermal affected zone thickness of the textures. Results of rough/colored combined textures allow opening new perspectives in industrial design, particularly in aesthetic applications with special properties.
ARTICLE | doi:10.20944/preprints201906.0150.v1
Subject: Engineering, General Engineering Keywords: laser diode; wavelength; stimulated emission; temperature effect
Online: 16 June 2019 (16:53:46 CEST)
The present work is a theoretical and experimental study of temperature effect on wavelength and threshold current. Since Semiconductor lasers are the type of lasers which uses semiconductor material as a gain medium to achieve stimulated emission of radiation. In this module, the type of semiconductor lasers use is VCSEL and laser diode. Temperature change cause Semiconductor lasers to shift its threshold current, this variation also causes a shift in output wavelength. The experimental results highly agreement with the theoretical calculations.
ARTICLE | doi:10.20944/preprints201901.0127.v1
Subject: Materials Science, Nanotechnology Keywords: metal nanoparticles; laser ablation; antibacterial test; LSPR
Online: 14 January 2019 (07:21:21 CET)
We report the production of metal oxide (TiFe2O4, ZnFe2O4) nanoparticles by pulsed laser ablation technique in liquid environment. We used nano second Nd: YAG laser systems working at 532 nm and 1064 nm of wavelength, the energy of the laser beam was kept constant at 80 mJ. Absorbance spectra, surface plasmon resonance, optical band-gap and nanoparticle morphology were investigated using ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Changing the wavelength of the laser for growth, nanoparticles shown shift between the absorbance and surface plasmon resonance peaks in their UV-Vis spectra, this implies that the optical properties of the colloid nanoparticles depends on laser parameters, this was confirmed with the variation of the band gap energy. Furthermore, red shift for the absorbance peak was observed for samples as-growth at 532 nm around the 150 nm as function of time preparation. Whereas, for the samples as-growth at 1064 nm there is no shift in the absorbance spectra, this can be due to agglomeration and formation of larger particles. The characterization results shown appropriate plasmonic photo-catalysts properties of the particles, hence the photo activation of the nanoparticles was examined on antibacterial effect using colonies of Staphylococcus Aureus and Escherichia coli.
ARTICLE | doi:10.20944/preprints201806.0252.v1
Subject: Materials Science, Surfaces, Coatings & Films Keywords: laser cladding; powder flow; 316L stainless steel
Online: 15 June 2018 (11:50:29 CEST)
Laser Cladding is one of the leading processes within Additive Manufacturing technologies, a fact which has concentrated an important amount of effort on its development. In regard to the latter, the current study aims to summarize the influence of the most relevant process parameters in the laser cladding processing of single and compound volumes (solid forms) made from AISI 316L stainless steel powders and using a coaxial nozzle for deposition. Process speed, applied laser power and powder flow are considered to be the main variables affecting laser cladding in single clads, meanwhile overlap percentage and overlapping strategy become also relevant when dealing with multiple clads. By means of setting appropriate values of each process parameter, the main goal of this paper is to develop a processing window in which a good metallurgical bond between the delivered powder and substrate is obtained, trying simultaneously to maintain processing times in their lowest value possible. Conventional metallography techniques were performed on the cross sections of the laser tracks to measure the effective dimensions of clads for dilution analysis, height and width for the values of overlap between contiguous clads and layers, and also to analyze them for physical defects such as porosity and cracks. The resulting solid piece was 8 mm high at 800 mm/min.
ARTICLE | doi:10.20944/preprints201805.0287.v1
Online: 22 May 2018 (05:47:25 CEST)
The article presents tests aimed to verify the possibility of making T-joints in TMCP steel using laser. The tests involved the use of 10 mm thick high yield point steel S700MC obtained in an industrial manufacturing process. The joints made in the tests were single and double-sided. Subsequent non-destructive tests revealed that the joints obtained in the tests represented quality level B in accordance with PN-EN ISO 13919-1. Single-sided welding performed using the laser beam having a power of 11 kW enabled the obtainment of 8 mm deep penetration without visibly deforming the web of the joint. The double-sided welded joints were characterised by proper geometry and the presence of gas pores in the welds not compromising the requirements of quality level B (strict requirements). The weld structure was bainitic-ferritic. The weld hardness was by approximately 60 HV1 higher than that of the base material (280 HV1). The HAZ area was slightly softer than the base material. The tests of thin foils performed using a high-resolution scanning transmission electron microscope revealed that, during welding, an increase in the content of the base material in the weld was accompanied by an increase in contents of alloying microagents Ti and Nb, particularly near the fusion line. The above-named alloying microagents, in the form of fine-dispersive (Ti,Nb)(C,N) type precipitates, could reduce plastic properties of joints.
ARTICLE | doi:10.20944/preprints201804.0095.v1
Subject: Materials Science, Nanotechnology Keywords: carbonization; laser annealing; mesophase; graphitization; porous carbon
Online: 8 April 2018 (12:07:13 CEST)
Porous graphite was prepared without the use of template by rapidly heating the carbonization products from mixtures of anthracene, flourene, and pyrene with a CO2 laser. Rapid CO2 laser heating at a rate of 1.8 × 10 6 °C/s vaporizes out the fluorene-pyrene derived pitch while annealing the anthracene coke. The resulting structure is that of graphite with 100 nm spherical pores. The graphitizablity of the porous material is the same as pure anthracene coke. Transmission electron microscopy revealed that the interface between graphitic layers and the pore walls are unimpeded. Traditional furnace annealing does not result in the porous structure as the heating rates are too slow to vaporize out the pitch, thereby illustrating the advantage of fast thermal processing. The resultant porous graphite was prelithiated and used as an anode in lithium ion capacitors. The porous graphite when lithiated had a specific capacity of 200 mAh/g at 100 mA/g. The assembled lithium ion capacitor demonstrated an energy density as high as 75 Wh/kg when cycled between 2.2 V to 4.2 V.
ARTICLE | doi:10.20944/preprints201710.0172.v1
Subject: Engineering, Civil Engineering Keywords: laser; construction monitoring; measurements; uncertainty; bridge inspection
Online: 27 October 2017 (16:17:23 CEST)
Recent researches proved that the underbridge geometry can be reconstructed by mounting a 3D laser scanner on a motorized cart travelling on a walkway located under the bridge. The walkway is moved by a truck and the accuracy of the bridge model depends on the accuracy of the trajectory of the scanning head with respect to a fixed reference system. In this paper, we describe the metrological characterization of a method that uses non-contact systems to identify the relative motion of the cart with respect to the walkway; the orientation of the walkway with respect to the bridge is determined using inclinometers and optical rails, while the position of the truck with respect to the bridge is measured using a conventional odometer. The measurement uncertainty of the proposed system was initially evaluated by numerical simulations and successively verified by experiments in laboratory conditions. The complete system has then been tested in operative conditions; the validity of the proposed approach has been demonstrated by comparing the geometry of buildings reconstructed with the proposed system with the geometry obtained with a static scan. Results evidenced that the errors are approximately 6 mm.
ARTICLE | doi:10.20944/preprints201703.0186.v1
Subject: Medicine & Pharmacology, Veterinary Medicine Keywords: veterinary; allergic dermatitis; low level laser therapy
Online: 24 March 2017 (10:32:49 CET)
Background: The prevalence of atopic dermatitis in domestic animals is one of the problems of modern veterinary. Treating with standard techniques using chemotherapeutic agents not always leads to a positive result of therapy; moreover, many drugs produce adverse side effects. Methods: Low level laser therapy, in particular, intravenous laser blood illumination (ILBI) has a pronounced and long-lasting impact on the immune system of animals. The combined technique including ILBI-635 (635 nm, 2 mW, 5 min) and LUVBI® (365 nm, 2 mW, 3 min) every other day provides a positive change in clinical status of cats with allergic dermatitis after the 3rd-4th treatment session. Results: The increased level of erythrocytes and hemoglobin was identified in the course of treatment, and it indirectly indicates increased blood transport activity, which improves trophic provision and microcirculation. A double reduction of leukocytes and a significant decrease of neutrophil cells indicate the immunomodulatory effect of LILI (low-intensity laser illumination). The increase in the percentage of lymphocytes and the decrease of eosinophils and monocytes against the background of basophil concentrations deviations within physiological concentration result in the reduction of inflammatory mediators expression that induce itching. The reduction of total IgE concentration 32 times against control on the 7th day of treatment correlates with the decrease in the quantitative content of peripheral blood eosinophils, indicating the decrease in severity of an allergic process. Conclusion: LLLT is recommended against the background of standard drug therapy to achieve quick clinical outcome together with a long-lasting prolonged effect.
ARTICLE | doi:10.20944/preprints201812.0125.v1
Subject: Materials Science, Nanotechnology Keywords: pulsed laser ablation in water; pulsed laser ablation in air; ZnO nanoparticles; biomedical materials; PLLA-scaffold; antibacterial properties
Online: 11 December 2018 (10:32:20 CET)
Here, we report on ZnO nanoparticles (NPs) generated by nanosecond pulsed laser (Nd:YAG, 1064 nm) through ablation of metallic Zn target in water and air and their comparative analysis as potential nanomaterials for biomedical applications. The prepared nanomaterials were carefully characterized in terms of their structure, composition, morphology and defects. It was found that in addition to the main wurtzite ZnO phase, which is conventionally prepared and reported by others, the sample laser-generated in air also contained some amount of monoclinic zinc hydroxynitrate. Both nanomaterials were then used to modify model wound dressings based on biodegradable poly-L-lactic acid. The as-prepared model dressings were tested as biomedical materials with bactericidal properties towards S. aureus and E. coli strains. The advantages of the NPs prepared in air over their counterparts generated in water found in this work are discussed.
ARTICLE | doi:10.20944/preprints202101.0622.v1
Subject: Keywords: LPBF; Laser Powder Bed Fusion; SLM; Selective Laser Melting; High-speed steel; tool steel; high carbon content; preheating temperature
Online: 29 January 2021 (13:09:59 CET)
Laser powder bed fusion (LPBF) is an additive manufacturing process employed in many industries, for example for aerospace, automotive and medical applications. In these sectors, mainly nickel-, aluminum- and titanium-based alloys are used. In contrast, the mechanical engineering industry is interested in more wear-resistant steel alloys with higher hardness, both of which can be achieved with a higher carbon content, like in high-speed steels. Since these steels are susceptible to cracking, preheating needs to be applied during processing by LPBF. In a previous study, we applied a base plate preheating temperature of 500 °C for HS6-5-3-8 with 1.3 % carbon content. We were able to manufacture dense (p > 99.9 %) and crack-free parts from HS6-5-3-8 with a hardness > 62 HRC (as built) by LPBF. In this study, we investigate the influence of preheating temperatures up to 600 °C on hardness and microstructure dependent on part height for HS6-5-3-8. The microstructure was studied by light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The analysis of hardness and microstructure at different part heights is necessary because state-of-the-art preheating systems induce heat only into the base plate. Consequently, parts are subjected to temperature gradients and different heat treatment effects depending on part height during the LPBF process.
Subject: Physical Sciences, Atomic & Molecular Physics Keywords: plasma diagnostics; molecular spectra; diatomic molecules; plasma spectroscopy; laser spectroscopy; laser-induced breakdown spectroscopy; optical emission spectroscopy; hypersonic expansion
Online: 15 January 2020 (07:12:25 CET)
This article reports new measurements of laser-induced plasma hypersonic expansion measurements of diatomic molecular cyanide (CN). Focused, high-peak power 1064-nm Q-switched radiation of the order of 1 TW/cm2 generates optical breakdown plasma in a cell containing a 1:1 molar gas mixture of N2 and CO2 at a fixed pressure of 1.1 × 105 Pascal and in a 100 ml/min flow of the mixture. Line-of-sight (LOS) analysis of recorded molecular spectra indicate the outgoing shockwave at expansion speeds well in excess of Mach number 5. Spectra of atomic carbon confirm an increased electron density near the shock wave, and equally, molecular CN spectra reveal higher excitation temperature near the shockwave. The results are consistent with corresponding high-speed shadow graphs obtained by visualization with an effective shutter speed of five n anosecond. In addition, LOS analysis and application of integral inversion techniques allow inferences about the spatio-temporal distribution of the plasma.
ARTICLE | doi:10.20944/preprints201812.0119.v1
Subject: Physical Sciences, Applied Physics Keywords: 3D nano-lithography, 3D laser lithography, direct laser writing, nanopolymerization, cross-linking, multi-photon absorption, avalanche ionization, temperature effects
Online: 11 December 2018 (09:31:31 CET)
Direct laser writing three-dimensional nano-lithography is an established technique for manufacturing functional 3D micro- and nano-objects via non-linear absorption induced polymerization process. In this Chapter an underlying physical mechanisms taking place during nano-confined polymerization reaction, induced by tightly focused ultra-short laser pulses, are reviewed and discussed. The special attention is paid on the effects that directly impact structuring resolution and minimum achievable feature size. Analysis of possible photo-initiation mechanisms as contributing multi-photon absorption and avalanche ionization in pre-polymers under diverse exposure conditions (wavelength, pulse duration) is presented. Feasible structuring of pure (non-photosensitized) and functional nanoparticles doped polymer precursors is justified and benefits of such materials/structures for microoptics, photonics and cell scaffolds are highlighted. The influence of temperature effects (induced by writing process itself or determined by ambient conditions) on polymerization process, observed in different pre-polymers under diverse exposure regimes is outlined. The further adjustment of the structuring resolution is possible via precise control of light polarization and diffusion assisted radical quenching. The work is concluded with a brief outlook on future challenges and perspectives related to refinement of 3D ultra-fast laser lithography fabrication process in the means of application of diverse post-processing methods and research into novel photo-curable materials including inorganic ones.
ARTICLE | doi:10.20944/preprints201810.0384.v1
Subject: Physical Sciences, Applied Physics Keywords: direct laser writing, multiphoton processing, laser 3D nanolithography, optical 3D printing, microstructures, nanotechnology, mesoscale, two-photon polymerization, microoptics, SZ2080
Online: 17 October 2018 (11:26:32 CEST)
3D meso-scale structures that can reach up to centimeters in overall size but retain micro- or nano-features, proved to be promising in various science fields ranging from micro-mechanical metamaterials to photonics and bio-medical scaffolds. In this work we present synchronization of the linear and galvano scanners for efficient femtosecond 3D optical printing of objects at the meso-scale (from sub-μm to sub-cm spanning five orders of magnitude). In such configuration the linear stages provide stitch-free structuring at nearly limitless (up to tens-of-cm) working area, while galvo-scanners allow to achieve translation velocities in the range of mm/s-cm/s without sacrificing nano-scale positioning accuracy and preserving undistorted shape of the final print. The principle behind this approach is demonstrated, proving its inherent advantages in comparison to separate use of only linear stages or scanners. The printing rate is calculated in terms voxels/s, showcasing the capability to maintain an optimal feature size while increasing throughput. Full capabilities of this approach are demonstrated by fabricating structures that reach millimeters in size but still retain μm-scale features: scaffolds for cell growth, microlenses and photonic crystals. All this is combined into a benchmark structure: a meso-butterfly. Provided results show that synchronization of two scan modes is crucial for the end goal of industrial-scale implementation of this technology and makes the laser printing well aligned with similar approaches in nanofabrication by electron and ion beams.
ARTICLE | doi:10.20944/preprints202204.0018.v1
Subject: Physical Sciences, Applied Physics Keywords: Droplet; Laser shock; High temperatures; Dynamics; Focusing enhancement
Online: 4 April 2022 (12:02:37 CEST)
The temperature-assisted laser shock process has shown promising prospects in the fields of forming manufacturing and surface strengthening. However, large-scale application of this process is limited by the instability and failure of confinement medium at high temperatures (≥300 ℃). Aiming at this problem, we propose a novel laser shock strategy based on Leidenfrost effect, where the suspended droplets are utilized as the confinement medium. According to the sequence of images acquired by time delay system and high-speed camera, the droplet dynamics behavior is studied. The focusing enhancement effect of the droplet is comprehensively explored. And the correlations between droplet size, ambient temperature, vapor layer thickness and focusing effect are investigated. Combining the dynamics and focusing enhancement effect of droplets, a theoretical model of laser shock pressure under droplet confinement is established. Finally, the effectiveness and feasibility of the droplet-based laser shock strategy in high temperature processing environments are verified by typical applications in laser shock forming and laser shock peening fields. The results show that the droplet-based laser shock process presents better forming effect. And the mechanical property tests demonstrate that this process can obtain the simultaneous improvement of the strength (~51%) and ductility (~6.4%) of annealed Cu. The multiscale plasticity mechanisms of the strengthened material are comprehensively investigated. We believe that this low-energy, low-cost and high-quality process can provide a new solution for the industrial application of laser shock at high temperatures.
REVIEW | doi:10.20944/preprints202202.0258.v1
Subject: Materials Science, Nanotechnology Keywords: plasmonics; nanoscale; ablation; direct laser write; die-met
Online: 21 February 2022 (14:54:57 CET)
Nanoscale structuring/printing is of interest for range of applications in 3D subtractive and additive manufacturing (3D+/-). Basic principles of light field enhancement and control at the nanoscale are overviewed in this section/chapter for bulk, surface, and localised plasmons (1D, 2D, and 3D localisation, respectively). All these plasmons are resonant phenomena which have common Lorentzian spectral lineshape which relates refractive and absorption properties as well as defining the phase of transmitted and scattered light. Localisation of light at the nanoscale creates the possibility of modification with matching resolution. Harnessing this light enhancement can be demonstrated as a "nano-pen" for direct write nanolithography.
ARTICLE | doi:10.20944/preprints202201.0169.v1
Online: 12 January 2022 (13:50:07 CET)
Numerical calculations of ultraviolet to near-infrared absorption spectra by cadmium selenide quantum dots (CdSe QDs) doped in anodic aluminum oxide pores were performed using a finite-difference time-domain model. The height, diameter, and periodic spacing of the pores were optimized. Light absorption by the dots was enhanced by increasing the height and decreasing the diameter of the pores. When the height was less than 1 μm, visible light absorption was enhanced as the spacing was reduced from 400 nm to 100 nm. No enhancement was observed for heights greater than 6 μm. Finally, the optical mode coupling of the aluminum oxide and the quantum dots was enhanced by decreasing the pore diameter and periodic spacing, and increasing the height. Laser ablation verified light absorption enhancement by the CdSe QDs. The experiment verified the improvement of the laser-induced damage ability with wavelength of 355-nm after aluminum alloy 6061 coated with functional films, which was fabricated based on numerical calculations.
ARTICLE | doi:10.20944/preprints202106.0699.v1
Subject: Biology, Anatomy & Morphology Keywords: pollen, pollen classes, determination, 3D, laser scanning microscopy
Online: 29 June 2021 (11:45:54 CEST)
Pollen analysis as a part of palynology deals with the morphological determination of pollen and spores. Different technologies with different resolutions varying from simple light microscopy to highly elaborate electron microscopy are used for the examination, depending on the area of application (e.g. sedimentology, melissopalynology, forensic palynology, etc.). To answer the question of whether laser scanning microscopy (LSM) can replace scanning electron microscopy (SEM) for the determination of pollen species, 168 species were examined using LSM. It was concluded that LSM is both efficient and easy to handle. After preparing the fresh pollen, a 3D laser scan takes 5-10 minutes and unlike using SEM, the pollen does not have to be sputtered or processed. The 3D scans can be measured quickly and easily with the integrated software and there were no observable artifacts. At magnifications up to 8545x, the image quality is comparable to that of a sputtered SEM sample whereas at higher magnifications, the SEM method is superior. Overall, pollen display by LSM is much less time consuming and more cost effective than with the SEM method.
Online: 2 April 2021 (11:24:50 CEST)
Pain is an unpleasant emotional and sensory experience. For many years orthodontists have been looking for an effective method of reducing this feeling of discomfort. In recent years, low-level laser therapy (LLLT) has taken hold in the orthodontic field. Among the countless advantages it can modulate the painful feeling. The aim of this research is to identify the use of photobiomodulation in subjects undergoing fixed orthodontic treatment, to reduce the pain and discomfort that it causes. The research was conducted from the Web of Science, Pubmed and Scopus databases. Only 14 of all articles met the inclusion and exclusion criteria and were therefore used to conduct the research. The different studies compared, in most cases, patients whose mouth was divided into a part treated with laser therapy and a placebo part. The results show a statistically significant difference in perceived pain between the irradiated arch and the non-irradiated arch. Three authors didn’t find statistically significant results in favour of low-laser therapy, but it is important to remember that they used different parameters. To obtain generally valid studies, with consistent and reproducible results, it is necessary to standardize the different parameters used that are independent by operator performing the procedure.
Subject: Physical Sciences, Acoustics Keywords: spatial light modulators; laser trapping; holographic optical tweezers
Online: 26 March 2021 (15:10:07 CET)
Spatial light modulators (SLMs) have been widely used to achieve dynamic control of optical traps. Often, holographic optical tweezers have been presumed to provide nanometer or sub-nanometer positioning accuracy. It is known that some features concerning the digitalized structure of SLMs cause a loss in steering efficiency of the optical trap, but their effect on trap positioning accuracy has been scarcely analyzed. On the one hand, the SLM look-up-table, which we found to depend on laser power, produces positioning deviations when the trap is moved at the micron scale. On the other hand, phase quantization, which makes linear phase gratings become phase staircase profiles, leads to unexpected local errors in the steering angle. We have tracked optically-trapped microspheres with sub-nanometer accuracy to study the effects on trap positioning, which can be as high as 2 nm in certain cases. We have also implemented a correction strategy that enabled the reduction of errors down to 0.3 nm.
ARTICLE | doi:10.20944/preprints202101.0596.v1
Subject: Engineering, Automotive Engineering Keywords: Laser; Polishing; Additive manufacturing; Surface analysis; Identification; Topography
Online: 28 January 2021 (22:22:21 CET)
One of the challenges facing the industrial adoption of additively manufactured parts is the surface roughness on the as-built part. The surface roughness of parts is frequently characterized by metrics specified by international standards organizations. However, these standards list many surface metrics that can make it unclear which to use to best describe the surface. In this work, the ability of the various surface metrics to successfully classify the as-built and post-processed surfaces is studied using linear classification models. Laser polishing via remelting and manual grinding are the post-processing techniques used to smooth the as-built surface. The ability of the linear classifier to successfully categorize the various surfaces is demonstrated, and the various surface metrics are ranked according to the strength of their individual ability to classify the surfaces. This work promotes the method as a potential way to autonomously classify as-built and laser polished surfaces.
ARTICLE | doi:10.20944/preprints202006.0137.v1
Subject: Medicine & Pharmacology, Dentistry Keywords: Crown removal; Debond; Er:YAG; Laser; Lithium disilicate; Zirconia
Online: 11 June 2020 (12:06:51 CEST)
The study examined the effect of noninvasive crown retrieval/reuse process using erbium-doped yttrium aluminum garnet laser (Er:YAG). Twenty-six extracted human teeth were prepared for a crown. The crown was milled using lithium disilicate (LD) and zirconia (Z) materials, n=13 per group, 3 for scanning electron microscopy (SEM). The crown was luted using composite resin cement and subjected to a laser retrieval process. After the retrieval process, the crown was cleaned, recemented and laser-retrieved two more times, without and with additional tooth reduction mimicking clinical refreshment of dentin. Retrieval time and temperature were analyzed using analysis of variance (ANOVA). Surface changes were observed through SEM. The retrieval times were 267.1±130.43, 220±79.09, 277.1±126.44, 368.4±136.14, 355±159.39, and 419.2±121.36 seconds for first, second, third LD and Z groups, respectively (p=.009). The maximal temperatures were 23.95.1±1.89°C, 24.86±2.01°C, 24.17±1.53°C, 22.88±1.51°C, 24.03±1.74°C, and 21.99±1.32°C for for first, second, third LD and Z groups, respectively (p=.006). Er:YAG laser crown removal is an effective retrieval tool for all-ceramic crowns. Minimal changes to teeth and crowns were observed following laser irradiation.
ARTICLE | doi:10.20944/preprints202004.0260.v1
Subject: Engineering, Biomedical & Chemical Engineering Keywords: Ear-EEG; laser structuring; porous platinum; Berger effect
Online: 16 April 2020 (07:39:35 CEST)
The interest in dry EEG electrodes has increased in recent years and especially as everyday suitability earplugs for measuring drowsiness or focus of auditory attention. However, the challenge is still the need for a good electrode material, which is reliable and can be easily processed for highly personalized applications. Laser processing as used here is a fast and very precise method to produce personalized electrode configurations that meet the high requirements of in-ear EEG electrodes, for example. The arrangement of the electrodes on the very flexible and compressible mats allows an exact alignment of the electrodes to the ear mold and contributes to a high wearing comfort, as no edges or metal protrusions are present. For better transmission properties, an adapted coating process for surface enlargement of platinum electrodes is used, which allows easy control of the thickness and growth form of the porous layer. The porous platinum-copper alloy is chemically very stable, shows no exposed copper residues and enlarges the effective surface area by 40. In a proof-of-principle experiment, these porous platinum electrodes could be used to measure the Berger effect in a dry state using just one ear of a test person. Their signal-to-noise ration and frequency transfer function is comparable to gel-based silver/silver chloride electrodes.
ARTICLE | doi:10.20944/preprints202003.0055.v1
Subject: Physical Sciences, Fluids & Plasmas Keywords: Beam dumps; laser plasma accelerator; plasma beam dump
Online: 4 March 2020 (09:45:00 CET)
Beam dumps are indispensable components for particle accelerator facilities to absorb or dispose beam kinetic energy in a safe way. However, the design of beam dumps based on conventional technology, i.e. the energy deposition via beam-dense matter interaction, makes the beam dump facility complicated and large in size, partly due to nowadays’ high beam intensities and energies achieved. In addition, these high-power beams generate radioactive hazards, which need specific methods to deal with. On the other hand, the EuPRAXIA project can advance the laser-plasma accelerator significantly by achieving 1-5 GeV high quality electron beam in a compact layout. Nevertheless, the beam dump based on conventional technique will still produce radiation hazards and make the overall footprint less compact. Here, we propose to implement a plasma beam dump to absorb the kinetic energy from the EuPRAXIA beam. In doing so, the overall compactness of the EuPRAXIA layout will not be impacted, and the radioactivity generated by the facility can be mitigated. In this paper, results from particle-in-cell (PIC) simulations are presented for plasma beam dumps based on EuPRAXIA beam parameters.
ARTICLE | doi:10.20944/preprints201907.0058.v1
Subject: Mathematics & Computer Science, General & Theoretical Computer Science Keywords: laser scanning; point cloud; tree modelling; precision forestry
Online: 3 July 2019 (09:38:08 CEST)
Laser scanning is an effective tool for acquiring geometric attributes of trees and vegetation, which lays a solid foundation for 3-dimensional tree modelling. Existing studies on tree modelling from laser scanning data are vast. Nevertheless, some works don’t ensure sufficient modelling accuracy, while some other works are mainly rule-based and therefore highly depend on user inputs. In this paper, we propose a novel method to accurately and automatically reconstruct tree branches from laser scans. We first extract an initial tree skeleton from the input tree point cloud, then simplify the skeleton through iteratively removing redundant components. A global-optimization approach is performed to fit a sequence of cylinders to approximate the geometry of the tree branches. Experiments on various types of trees from different data sources demonstrate the effectiveness and robustness of our method. The resulted tree models can be further applied in the precise estimation of tree attributes, urban landscape visualization, etc.
REVIEW | doi:10.20944/preprints201901.0213.v1
Subject: Physical Sciences, Optics Keywords: inorganic perovskites; hybrid perovskites; stimulated emission; laser devices
Online: 22 January 2019 (11:14:55 CET)
Inorganic and organic – inorganic (hybrid) perovskite semiconductor materials have attracted the worldwide scientific attention and research effort as the new wonder material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential as competitors to the dominant silicon solar cells technology. However, the fundamental principles in Physics dictate that an excellent material for photovoltaic applications must be also an excellent light emitter. This has been realized for the case of perovskite based light emitting diodes (LEDs) but much less for the case of the respective laser devices. Here, the strides have been made since 2014 are presented for the first time. The solution processability, low temperature crystallization, formation of nearly defect free, nanostructures, the long range ambipolar transport, the direct energy band gap, the high spectral emission tunability over the entire visible spectrum and the almost 100% external luminescence efficiency show perovskite semiconductors’ potential to transform the nanophotonics sector. The operational principles, the various adopted material and laser configurations along the future challenges are reviewed and presented in this paper.
ARTICLE | doi:10.20944/preprints201811.0010.v1
Subject: Physical Sciences, Optics Keywords: forecasting; complex dynamics; fiber laser; chaos; ordinal patterns
Online: 2 November 2018 (04:21:25 CET)
Being able to forecast events is of great importance in many fields, from brain behavior to earthquakes or stock markets. Because each dynamical system has intrinsic features, different statistical tools have to be used for each system. Here we study the time series of the output intensity of a fiber laser with an ordinal patterns analysis, and we look for temporal correlations in order to statistically forecast the most intense events. We set two thresholds, a low one and a high one, to distinguish between low intensity versus high intensity events. We find that when the time series is performing events below the low threshold it shows some preferred temporal patterns before performing events above a high threshold.
ARTICLE | doi:10.20944/preprints201809.0330.v1
Subject: Materials Science, Nanotechnology Keywords: elastic properties; laser ultrasonic; mechanical behavior; fiber-network
Online: 18 September 2018 (08:16:18 CEST)
For development and successful application of any material, a clear understanding of their mechanical behavior is one of the most important things, but when it comes to nanofibers networks it become a challenge due to, their high porosity, many scales in their structure, and characteristics non-linear. Therefore, an experimental methodology in conjunction with a theoretical model that can fully consider their characteristics is still needed. In this work we proposed a model that incorporates the propagation of the elastic waves in two-phase media to determine the effective elastic modulus of electrospun membranes of PLA/gelatin given the mechanical properties of nanofibers, shape, distribution and concentration. The model was verified via laser ultrasonic testing. It was found that the values predicted for the effective modulus by the model were higher than the values obtained from experimental results. One explanation is due to the experimental density. As a result, the P-Wave velocity from the model best fit to experimental results and it has the same behavior, decrees as the concentration of gelatin in the solution. These results indicate the model and experimental methodology can assist in the dressing of nanofibers networks and electrospun materials.
BRIEF REPORT | doi:10.20944/preprints201806.0086.v1
Subject: Medicine & Pharmacology, Dentistry Keywords: er:yag laser; debonding; laminate veneer; scanning electron microscopy
Online: 6 June 2018 (11:53:01 CEST)
The purpose of this study consists to verify if Er:YAG laser, at low fluences, is able to debond porcelain veneers, successfully used to improve anterior tooth esthetics, without damaging the tooth structures. A total of twelve freshly extracted teeth were used and samples were decontaminated, stored, prepared to obtain Veneers adhesion. One week after, Er:YAG laser with a non-contact sapphire tip with air-water spray was used for veneer debonding at 100 mJ of power and 30Hz of frequency (Fluence 5.91 J/cm2). Results demonstrated that veneer debonding is possible with an Er:YAG laser and that the total number of pulses does not seem related to its efficiency. SEM observation confirms that residual tooth structure is not altered when using these low fluences. Low fluences with Er:YAG laser are able to debond veneers while preserving the tooth structures. SEM observation confirmed that residual tooth structure is not altered with low fluences.
ARTICLE | doi:10.20944/preprints201803.0197.v1
Subject: Engineering, Biomedical & Chemical Engineering Keywords: laser micromachining; scaffold; biomimetics; microadditive manufacturing; microsubtractive manufacturing
Online: 23 March 2018 (08:00:52 CET)
The development of organ-on-chip and biological scaffolds is currently requiring simpler methods to microstructure biocompatible materials in three dimensions, fabricate structural and functional elements in biomaterials or modify the physicochemical properties of desired substrates. Aiming at addressing this need, a low-power CD-DVD-Blu-ray laser pickup head was mounted on a programmable three-axis micro-displacement system in order to modify the surface of polymeric materials in a local fashion. Thanks to a specially-designed method using a strongly absorbing additive coating the materials of interest, it has been possible to establish and precisely control processes useful in microtechnology for biomedical applications. The system was upgraded with blu-ray laser for additive manufacturing and ablation on a single platform. In this work, we present the application of these fabrication techniques to the development of biomimetic cellular culture platforms thanks to the simple integration of several features typically achieved with traditional, less cost-effective microtechnology methods in one step or through replica-molding. Our straightforward approach indeed enables great control of local laser microablation or polymerization for true on-demand biomimetic micropatterned designs in transparent polymers and hydrogels and is allowing integration of microfluidics, microelectronics, surface microstructuring and transfer of superficial protein micropatterns on a variety of biocompatible materials.
ARTICLE | doi:10.20944/preprints201906.0134.v1
Subject: Physical Sciences, Fluids & Plasmas Keywords: atomic and molecular spectroscopy; time-resolved spectroscopy; laser plasma; laser-induced optical breakdown; stellar astrophysics spectra; white dwarf stars; hydrogen
Online: 14 June 2019 (15:01:44 CEST)
This work communicates laser-plasma experiments in a gaseous mixture of hydrogen and nitrogen. Time-resolved spectroscopy measures the first four Balmer series hydrogen lines together with selected neutral and ionized nitrogen lines. Optical breakdown plasma is generated in a 1:1 hydrogen:nitrogen mixture at ambient temperature and 0.27-atm pressure. Time-resolved spectroscopy records emitted radiation with spatial resolution along the slit height for the Hα, Hβ, Hγ, and Hδ lines. For 13 selected time delays from 0.25 µs to 3.25 µs and 0.025 µ gate-widths, micro-plasma diagnostics is evaluated. Of interest are the peak-separation and width of Hδ and width of Hγ for electron densities in the range of 0.1 to 1.0×1017 cm-3, and comparisons with Hβ and Hα diagnostics. Integral inversions interrogate spatial distributions of the plasma expansion. Applications include laboratory and stellar astrophysics plasma diagnosis.
ARTICLE | doi:10.20944/preprints201703.0202.v3
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: additive manufacturing; 3-D printing; metal additive manufacturing; selective laser melting; SLM; direct metal laser sintering; DMLS; metal powder processing
Online: 4 April 2017 (07:56:07 CEST)
A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce full-density metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion, and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization, and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging, and design-of-experiments), support structure optimization, and overhang feature design; approximately 140 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs, and potential future research directions are discussed in-depth in light of the present review.
ARTICLE | doi:10.20944/preprints201907.0033.v1
Subject: Physical Sciences, Atomic & Molecular Physics Keywords: laser-induced plasma; atomic spectroscopy; laser-induced breakdown spectroscopy; 29 atomic spectroscopy; principal component analysis; partial least-square regression; gypsum; Mars
Online: 2 July 2019 (08:03:52 CEST)
The first detection of gypsum (CaSO4.2H2O) by the Mars Science Laboratory (MSL) rover Curiosity in the Gale Crater, Mars created a profound impact on planetary science and exploration. The unique capability of plasma spectroscopy involving in situ elemental analysis in extraterrestrial environments, suggesting the presence of water in the red planet based on phase characterization and providing a clue to Martian paleoclimate. The key to gypsum as an ideal paleoclimate proxy lies in its textural variants, and in this study terrestrial gypsum samples from varied locations and textural types have been analyzed by Laser Induced Breakdown Spectroscopy (LIBS) technique. Petrographic, sub-microscopic and powder X-ray diffraction characterizations confirm the presence of gypsum (hydrated calcium sulphate; CaSO4.2H2O), bassanite (semi-hydrated calcium sulphate; CaSO4.1/2H2O) and anhydrite (anhydrous calcium sulphate; CaSO4) along with accessory phases (quartz and jarosite). The principal component analysis of LIBS spectra from texturally varied gypsums can be differentiated from one another because of the chemical variability in their elemental concentrations. The concentration of gypsum is determined from the partial least-square regressions model. Rapid characterization of gypsum samples with LIBS is expected to work well in extraterrestrial environments.
ARTICLE | doi:10.20944/preprints202209.0392.v1
Subject: Materials Science, Surfaces, Coatings & Films Keywords: Laser induced forward transfer; high entropy alloys; micro-particles
Online: 26 September 2022 (10:32:29 CEST)
Controlled deposition of CoCrFeNiMo0.2 high entropy alloy (HEA) micro-particles was achieved using laser induced forward transfer (LIFT). Ultra-short laser pulses, 230 fs of 515 nm wavelength, were tightly focused into ∼ 2.4 μm focal spots on the ∼50 nm thick plasma-sputtered films of CoCrFeNiMo0.2. The HTA films were transferred onto glass substrates by magnetron sputtering in vacuum (10−8 atm) from the thermal spray coated substrates. The absorption coefficient of CoCrFeNiMo0.2 α ≈ 6 × 105 cm−1 was determined at 600 nm wavelength. The real and imaginary parts of refractive index (n + iκ) of HEA were determined from reflectance and transmittance using nano-films.
ARTICLE | doi:10.20944/preprints202208.0206.v1
Subject: Engineering, Electrical & Electronic Engineering Keywords: Laser Communications; Platform Jitter; Beam-pointing stability; Drone; CubeSat
Online: 11 August 2022 (03:38:22 CEST)
Adaption of laser communication terminals to airborne and lean-satellite platforms is now a vogue, made possible due to the progressing advancements in lightweight components and compactness of onboard electro-optical transceivers and control systems. This enables highly secured and superior data-transmission rates beyond multiple Gigabit/second on CubeSats and drones compared to Megabit/second rates offered by similar radio-transceivers form factors. However, laser-transmission links require a very stringent beam-pointing stability because they are easily perturbed by attitude variations and micro-vibrations generated by the host platform’s propulsion system or other mechanically active subsystems in proximity with the transmitter’s optical head. Severe line-of-sight jitter causes the downlink laser beam to drift from the targeted receiving system’s field-of-view, inducing pointing errors, increasing signal outage probability and information loss. We experimentally examine the platform jitter generated by the propellers of an hexacopter drone during ground operation and the attitude-control unit’s reaction wheels in a 6U CubeSat structure. We determined the vibration spectrum unique to these platforms and accordingly prescribe requirements for applicable optical fine pointing and disturbance isolation or suppression systems needed to achieve a high-fidelity laser-communication link.
ARTICLE | doi:10.20944/preprints202104.0563.v1
Subject: Physical Sciences, Acoustics Keywords: Single crystal diamond; micro-water jet guided laser; microchannel
Online: 21 April 2021 (09:05:14 CEST)
Two types of trenches cross-section in conventional vertical and brand new reverse-V-shape have fabricated on SCD substrate by micro-jet water-assist laser, the epitaxial lateral overgrowth technique has applied by microwave plasma chemical vapor deposition system in forming multiple micrometer-size channels. Raman and SEM techniques have applied in analyze both types growth layer characterization. Optical microscope has used to test microchannels hollowness. As a result, with the brand new reverse-V-shape trench, epitaxial lateral overgrowth layer reaches higher SCD surface morphology and crystal quality.
ARTICLE | doi:10.20944/preprints202104.0180.v1
Subject: Physical Sciences, Optics Keywords: MEMS Mirror Arrays; Laser beam; Fraunhofer Diffraction; Optical Intensity
Online: 6 April 2021 (13:47:01 CEST)
Compared with liquid crystal clad waveguide, MEMS mirror has some merits, such as high-er-transmissivity, lager-angle of scanning, faster scanning speed and so on. Furthermore, MEMS mirror arrays perform more superior than MEMS mirror when they steer laser beam, which make MEMS arrays much more suitable to be used in devising compact Lidar. Before assembling a Lidar with MEMS arrays, the optical intensity and distributions of the laser diffracted by MEMS arrays should be analyzed, but few published papers about this issue are available so far, this paper will focus on this issue about MEMS arrays. Firstly, the complex amplitudes of laser which is diffracted by 1-D and 2-D arrays are presented, respectively. Then the optical intensity and distributions on the observation plane are presented. Finally, the simulation diagrams of these distributions are shown, and the correctness of the results is indirectly verified by Young’s dou-ble-slit experiment. The results gotten in this letter are essential to design a compacted Lidar based on MEMS arrays.
ARTICLE | doi:10.20944/preprints202010.0007.v1
Subject: Medicine & Pharmacology, Allergology Keywords: debonding; Er,Cr:YSGG laser; primary teeth; RRIDs; zirconia crown
Online: 1 October 2020 (09:05:59 CEST)
(1) Background: Prefabricated zirconia crowns are used to restore teeth in children. The purpose of this study was to evaluate the removal of these crowns with the erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser; (2) Methods: Twelve primary and 13 permanent teeth were prepared and prefabricated zirconia crowns were passively fitted and cemented with two resin modified glass-ionomer cements. Surface areas of prepared teeth and crowns were calculated. Crowns were removed using two laser settings: 4.5 Watts, 15 Hertz, 20 water/ 20 air, and 5 Watts, 15 Hertz, 50 water/50 air. The retrieval time and temperature changes were tested recorded. Data were analyzed using ANOVA with Tuckey’s adjusted post hoc pairwise comparison t-test; (3) Results: The average time for crown removal was: 3 minutes, 47.7 seconds for permanent; and 2 minutes 5 seconds for primary teeth. The mean temperature changes were 2.48℃ (SD=1.43) for permanent; and 3.14℃ (SD=1.88) for primary teeth. The time to debond was significantly positively correlated with tooth inner surface area and volume, outer crown volume, and the cement volume; (4) Conclusions: Use of the Er,Cr:YSGG laser is an effective, safe and non-invasive method to remove prefabricated zirconia crowns cemented with RMGI cements from permanent and primary teeth.
ARTICLE | doi:10.20944/preprints202007.0509.v1
Subject: Medicine & Pharmacology, Ophthalmology Keywords: laser excimer; myopia surgery; long term; Femto-LASIK; PRK
Online: 22 July 2020 (09:53:46 CEST)
Refractive surgery is an increasingly popular procedure to decrease spectacle or contact lens dependency. The two most commonly used surgical techniques to correct myopia is Photorefractive keratectomy (PRK) and Femtosecond- Lasik (FS-LASIK)There are few publications that gathers such a long term follow up of both surgical techniques (2) Methods It has been performed a retrospective non-randomized study 509 PRK eyes and 310 FS-LASIK surgeries were followed for 10 years for the treatment of myopia and compound myopic astigmatism. Patients were followed up three months, one year, 2 years, 5 and 10 years. The safety index of both procedures was defined as a quotient between the postoperative BCVA (Best Corrected Visual Acuity) and the preoperative BCVA. The predictability is calculated as difference between the expected spherical equivalent and the achieved spherical equivalent. The efficacy index was calculated as a quotient between postoperative UCVA divided by the preoperative BCVA (3) Results. The results were: a safety index higher than 100% (109%) and an efficacy index of 82.4% after 10 years of PRK surgery in both groups. FS-LASIK was the safest surgery after 10 years and the most efficacy technique although in this case there were no statistically significant differences (4) Conclusions. All these data demonstrated better indexes for FS-LASIK
ARTICLE | doi:10.20944/preprints202007.0492.v1
Subject: Engineering, Mechanical Engineering Keywords: additive manufacturing; 316L steel; fatigue cracking; selective laser melting
Online: 21 July 2020 (13:34:49 CEST)
The effects of build orientation and heat treatment on the crack growth behavior of 316L stainless steel (SS) fabricated via a selective laser melting (SLM) additive manufacturing process were investigated. Significant growth of available research results of additively manufactured metallic parts still needs to be improved. The most important issue connected with properties after additive manufacturing is properties high anisotropy, especially from the fatigue point of view. The research included crack growth behavior of additively manufactured 316L in comparison to conventionally made reference material. Both groups of samples were obtained using precipitation heat treatment. Different build orientation in additively manufactured samples and rolling direction in reference samples were taken into account as well. Precipitation heat treatment of additively manufactured parts allowed to reach similar microstructure and tensile properties to elements conventionally made. The heat treatment positively affected fatigue properties. Additionally, precipitation heat treatment of additively manufactured elements significantly affected the reduction of fatigue cracking velocity and changed the fatigue cracking mechanism.
ARTICLE | doi:10.20944/preprints202007.0382.v1
Subject: Physical Sciences, Optics Keywords: Lithium niobate; laser processing; crystalline waveguide; liquid phase epitaxy.
Online: 17 July 2020 (14:08:30 CEST)
Low-loss photonic waveguides in lithium niobate offer versatile functionality as nonlinear frequency converters, switches, and modulators for integrated optics. Combining the flexibility of laser processing with liquid phase epitaxy we have fabricated and characterized lithium niobate channel waveguides on lithium niobate and lithium tantalate. We used liquid phase epitaxy with K2O flux on laser-machined lithium niobate and lithium tantalate substrates. The laser-driven rapid-prototyping technique can be programmed to give machined features of various sizes, and liquid phase epitaxy produces high quality single-crystal, lithium niobate channels. The surface roughness of the lithium niobate channels on a lithium tantalate substrate was measured to be 90 nm. The lithium niobate channel waveguides exhibit propagation losses of 0.26 ± 0.04 dB/mm at a wavelength of 633 nm. Second harmonic generation at 980 nm was demonstrated using the channel waveguides, indicating that these waveguides retain their nonlinear optical properties.
ARTICLE | doi:10.20944/preprints202001.0361.v1
Subject: Engineering, Mechanical Engineering Keywords: Additive manufacturing; FFF technology; Laser amplified ultrasonography; Tensile testing
Online: 30 January 2020 (11:05:28 CET)
The paper is focused on the examination of the internal quality of joints created in a multi-material - additive manufacturing process. The main part of the work focuses on experimental production and non-destructive testing of restrained joints of modified PLA (polylactic acid) and ABS (Acrylonitrile butadiene styrene) 3Dprinted on RepRap 3D device that works on the "open source" principle. The article presents the outcomes of non-destructive materials test in the form of the data from the Laser Amplified Ultrasonography, microscopic observations of the joints area and tensile tests of the specially designed samples. The samples with designed joints were additively manufactured of two materials: specially blended PLA (Market name – PLA Tough) and conventionally made ABS. The tests are mainly focused on the determination of the quality of material connection in the joints area. Based on the results obtained, the samples made of two materials were compared in the end to establish which produced material joint is stronger and have a lower amount of defects.
ARTICLE | doi:10.20944/preprints202001.0322.v1
Subject: Earth Sciences, Geology Keywords: Tengchongite; microscopic laser Raman spectroscopy; infrared spectroscopy; Yunnan Province
Online: 27 January 2020 (07:53:31 CET)
Tengchongite is a uranyl molybdate uranium mineral and it was found and named by Chen 1985.No more scholars studied on tengchongite after Chen’s work, The identification of this mineral has only been confirmed by single crystal X-ray diffraction. In the paper, micro laser Raman spectroscopy and infrared spectroscopy are used to identify the spectroscopy properties of tengchongite. The studies fill in the gaps of more than 30 years in terms of the molecular spectroscopy research of tengchongite. The mineral has an ideal model of Ca(UO2)6(MoO4)2O5•12H2O its bands attributed to the vibrating units are clearly identified in the Raman spectrum. Symmetric stretching modes at 812 cm-1 and 839 cm-1 are assigned to ν1 (UO2)2+ ,The ν3 antisymmetric stretching modes of (UO2)2+ are observed at 896 cm-1, Symmetric stretching modes at 419-1 and 440 cm-1 are assigned to ν2 (UO2)2+ .Symmetric stretching modes at 919cm-1 are assigned to ν1(MoO4)2-,The ν3 antisymmetric stretching modes of (MoO4)2- are observed at 752 cm-1, the in-plane ν2(MoO4)2-and the out-of-plane ν4(MoO4)2- bending modes are at 169 cm-1 and 254 cm-1. IR spectrum of tengchongite shows the major uranyl band at 858 cm-1 and 693 cm-1, Mo-O bonds are observed at about 985 cm-1 and 780 cm-1, and H2O groups are present with a wide range peaks from 3100 cm-1 to 3500 cm-1 and 1647 cm-1, and the band at 1432.4 cm-1 is probably due to the stretching vibration hydroxyl (OH-1), therefore, tengchongite contains may include hydroxyl and its chemical formula needs to be modified .
ARTICLE | doi:10.20944/preprints201909.0225.v1
Subject: Materials Science, Nanotechnology Keywords: magnetic nanoparticles; logic integrated platform; laser pyrolysis; nanosized materials
Online: 19 September 2019 (15:28:46 CEST)
We propose a concept of hybrid nanoelectronic-magnetic device for logic integrated platforms made of magnetic core-shell nanoparticles deposited onto prepatterned Si (111) substrate with basic logic circuitry made of metallic conductive lines. The synthesis of magnetic material and the creation of nanoelectronic prepatterned interdigitated die is reported and its capabilities are demonstrated in terms of magnetotransport properties. The laser pyrolysis method is employed in order to synthesize magnetic core-shell Fe / FeC nanoparticles with sizes between 12 – 15 nm. E-beam lithography has been used in order to design and execute two different layouts of interdigitated die, prepatterned with logic capacity, one with two pads and 50 microns thick conductive metallic lines, another one with 4 pads and parallel 5 microns thick conductive lines separated by 5 microns thick spacer. The as-obtained structures are morphologically characterized by means of optical, scanning and transmission electron microscopies. As-synthesized core-shell nanoparticles have been magnetically characterized inasmuch as the hybrid device obtained by depositing centrifugated and dispersed core-shell nanoparticles from liquid carrier solutions. For the first time, a significant giant magnetoresistive (GMR) effect has been observed and measured for the hybrid architectured device made of Fe / FeC nanosized materials on pre-patterned interdigitated die. A ∆R/R of 8% at 4.2 K has been measured from conductivity-in-plane electron transport measurements. This opens possibilities for the use of such devices as arrays of nanosensors and in spintronic applications.
ARTICLE | doi:10.20944/preprints201907.0337.v1
Subject: Physical Sciences, Optics Keywords: ultrafast laser microfabrication; 3D glass printing; light field manipulation
Online: 29 July 2019 (11:51:49 CEST)
Three-dimensional (3D) printing has allowed for production of geometrically complex 3D objects with extreme flexibility, which is currently undergoing rapid expansions in terms of materials, functionalities, as well as areas of application. When attempting to print 3D microstructures in glass, femtosecond laser induced chemical etching (FLICE) – which is a subtractive 3D printing technique – has proved itself a powerful approach. Here, we demonstrate fabrication of macro-scale 3D glass objects of large heights up to ~3.8 cm with an identical lateral and longitudinal spatial resolution of ~20 μm. The remarkable accomplishment is achieved by revealing an unexplored regime in the interaction of ultrafast laser pulses with fused silica which results in aberration-free focusing of the laser pulses deeply inside fused silica.
Online: 19 April 2019 (11:18:13 CEST)
This paper describes a multi-channel in-situ monitoring system developed to better understand defect formation signatures in metal additive manufacturing. Three high-speed imaging modes coupled with an image computer capable of processing and storing these data streams allowed an examination of defect formations signatures and mechanisms. It was found that defects later detected in X-ray computed tomography (CT) scans were related to regions with anomalous heat signatures and powder bed morphology. Automated defect detection algorithms based on these defect signatures captured 80% of defects greater than 300 µm.
ARTICLE | doi:10.20944/preprints201807.0133.v1
Subject: Engineering, Other Keywords: microfluidics; micro-injection-moulding; femtosecond laser micromachining; optical manipulation.
Online: 9 July 2018 (11:47:29 CEST)
Micro Injection molding combined with the use of removable inserts is one of the most promising manufacturing process for microfluidic devices, such as Lab-on-a-chip, that have the potential to revolutionize the healthcare and diagnosis system. In this work we have designed, fabricated and tested a compact and disposable plastic optical stretcher. To produce the mould inserts, two micro manufacturing technologies have been used. Micro Electro Discharge machining was used to reproduce the inverse of the capillary tube connection characterized by high aspect ratio. Thanks to the high accuracy of femtosecond laser machining, instead, we manufactured insert with perfectly aligned microfluidic channels and fiber slots, facilitating the final composition of the optical manipulation device. The optical stretcher operation is tested using microbeads and red blood cells solutions. The prototype presented in this work demonstrates the feasibility of this approach that should guarantee a real mass production of ready-to-use- Lab-on-a-chip.
ARTICLE | doi:10.20944/preprints201806.0400.v1
Online: 25 June 2018 (16:48:10 CEST)
The application of solvent method in the preparation of polypropylene powders was investigated, including the influence of various technological conditions, such as the raw material melt index of polypropylene, processing temperature, dosage of the solvent and the packing pressure. The experimental data show that using solvent method can effectively produce polypropylene powder, and the optimal technological conditions are: melt index of polypropylene being about 17.8 g/10min, processing temperature being about 166.0 ℃, dosage of the solvent being about 0.067g/ml and the packing pressure being about 0.7MPa.Under this technological conditions, polypropylene powder with excellent sphericity could be prepared, the apparent density of powder can reach 0.40 g/cm3 and the prepared powder displayed a narrow size distribution with the mean size of about 42.7 µm.
ARTICLE | doi:10.20944/preprints201802.0157.v1
Subject: Physical Sciences, Optics Keywords: biophotonic; Terahertz; time domain spectroscopy; absorption enhancement; laser cutting
Online: 26 February 2018 (09:30:06 CET)
In biology molecules and macromolecules like sugars, proteins, DNA, and RNA are of utter importance. Detecting their presence as well as their conformation is still a challenge in many cases. It is well known that the vibrational states of such molecules lie from the infrared to the TeraHertz range. Spectroscopy can be used to detect such compounds and probe their conformation. Still, terahertz spectroscopy on biosample is a challenge for two main reasons: water absorption; and the small size of the samples. The sample volume is smaller than the cube of the TeraHertz wavelength; the light matter interactions are thus extremely reduced. In this paper, we present the design, fabrication, characterization and the first typical uses of a biophotonic device aiming at increasing light matter interaction to enable terahertz spectroscopy of minute samples on a broad band (0.2–2 THz). We demonstrate time domain spectroscopy experiments on few µl samples showing the validity of our approach.
ARTICLE | doi:10.20944/preprints201708.0068.v1
Subject: Arts & Humanities, Architecture And Design Keywords: Terrestrial Laser Scanning; orthoimage; heritage; remote sensing; preservation; archaeology
Online: 18 August 2017 (16:49:13 CEST)
This article presents a methodology to process information from a Terrestrial Laser Scanner (TLS) from three dimensions (3D) to two dimensions (2D), and to two dimensions with a color value (2.5D), as a tool to document and analyze heritage buildings. Principally focused on the loss of material in stone, this study aims at creating an evaluation method for loss control, taking into account the state of conservation of the building in terms of restoration, from studying the pathologies, to their identification and delimitation. A case study on the Cathedral of the Seu Vella de Lleida was completed, examining the details of the stone surfaces. This cathedral was affected by military use, periods of abandonment, and periodic restorations.
REVIEW | doi:10.20944/preprints201705.0111.v1
Subject: Physical Sciences, Optics Keywords: random fiber laser; Lévy statistics; photonic spin-glass behavior
Online: 15 May 2017 (11:59:43 CEST)
The interest in random fiber lasers (RFLs), first demonstrated one decade ago, is still growing and their basic characteristics have been studied by several authors. RFLs are open systems that present instabilities in the intensity fluctuations due to the energy exchange among their non-orthogonal quasi-modes. In this work, we present a review of the recent investigations on the output characteristics of a continuous-wave erbium-doped RFL, with emphasis on the statistical behavior of the emitted intensity fluctuations. A progression from the Gaussian to Lévy and back to the Gaussian statistical regime was observed by increasing the excitation laser power from below to above the RFL threshold. By analyzing the RFL output intensity fluctuations, the probability density function of emission intensities was determined, and its correspondence with the experimental results was identified, enabling a clear demonstration of the analogy between the RFL phenomenon and the spin-glass phase transition. A replica-symmetry-breaking phase above the RFL threshold was characterized and the glassy behavior of the emitted light was established. We also discuss perspectives for future investigations on RFL systems.
ARTICLE | doi:10.20944/preprints202203.0393.v1
Subject: Engineering, Other Keywords: twisted optical fiber; chirality; laser beam profile; differential mode delay; laser-based few-mode optical signal transmission; fiber Bragg grating; few-mode effects
Online: 30 March 2022 (15:17:48 CEST)
This work presents results of property researches of fabricated samples of silica few-mode optical fiber (FMF) with induced chirality under twisting 10 and 66 revolutions per meter, core diameter 11 µm, typical “telecommunication” cladding diameter 125 µm and improved height of quasi-step refractive index profile. Proposed FMF supports 4 guided modes over “C”-band. We represent results of computed characteristics, as well as experimentally measured spectral responses of laser-excited optical signals, including researches and analysis of few-mode effects, occurring after fiber Bragg grating writing.
ARTICLE | doi:10.20944/preprints201905.0364.v1
Subject: Physical Sciences, Astronomy & Astrophysics Keywords: atomic and molecular spectroscopy; time-resolved spectroscopy; laser plasma; laser-induced optical breakdown; stellar astrophysics spectra; white dwarf stars; hydrogen; carbon Swan spectra
Online: 30 May 2019 (08:53:35 CEST)
This work discusses laboratory measurements of atomic and diatomic molecular species in laser-plasma generated in gases. Noticeable self-absorption of the Balmer series hydrogen alpha line occurs for electron densities of the order of one tenth of standard ambient temperature and pressure density. Emission spectra of selected diatomic molecules in air or specific gaseous mixtures at or near atmospheric pressure reveal minimal plasma re-absorption. Abel inversion of the plasma in selected gases and gas mixtures confirm expansion dynamics that unravel regions of atomic and molecular species of different electron temperature and density. Time resolved spectroscopy diagnoses self-absorption of hydrogen alpha and hydrogen beta lines in ultra-high pure hydrogen gas. Radiation from a Nd:YAG laser device induces micro-plasma for pulse widths in the range of 6 ns to 14 ns, energies in the range of 100 mJ to 800 mJ, and for peak irradiance of the order 1 to 10 TW/cm2. Atomic line profiles yield electron density and temperature from fitting of line profiles to wavelength and sensitivity corrected spectral radiance data. Analysis of measured diatomic emission data yields excitation temperature of primarily molecular recombination spectra. Applications of the laboratory experiments extend to investigations of stellar astrophysics white dwarf spectra.
ARTICLE | doi:10.20944/preprints201810.0729.v1
Subject: Materials Science, Nanotechnology Keywords: silver nanoparticles; laser ablation in liquids; laser synthesis of colloidal nanoparticle solution, nanoparticle impregnated paper; antimicrobial activity; fiber fines; sheet forming; vacuum filtration
Online: 30 October 2018 (16:14:31 CET)
A paper impregnated with silver nanoparticles (AgNPs) has been prepared. For the preparation of the substrates, aqueous suspensions of pulp fines, a side product from the paper production, have been mixed with Ag nanoparticles (AgNP) suspensions. The nanoparticle synthesis thereof was carried out via laser ablation of pure Ag in water. After the sheet formation process, the leaching of the AgNPs was determined to be low while the sheets exhibited antimicrobial activity towards E. Coli.
ARTICLE | doi:10.20944/preprints202202.0041.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: Laser scanning instrument; 3D scanner calibrator; surface reflectance; measurement accuracy
Online: 2 February 2022 (15:57:04 CET)
Abstract: The calibrator is one of the most important factors in the calibration of various laser 3D scanning instruments. The requirements for diffuse reflection surface are specially emphasized in many national standards. In this study, the spherical calibrator and plane calibrator compara-tive measurement experiments were carried out. The black ceramic standard sphere, white ce-ramic standard sphere, metal standard sphere, metal standard plane and white ceramic standard plane were used to test the laser 3D scanner. In the spherical calibrators comparative measure-ment experiments, the results indicated that the RMS of the white ceramic spherical calibrator with reflectance about 60% is 10 times that of the metal spherical calibrator with the reflectance of about 15%, and the RMS of the black ceramic spherical calibrator with reflectance of about 11% is of the same order as the metal spherical calibrator. In the plane calibrators comparative measurement experiments, the RMS of flatness measurement is 0.077 mm for metal plane cali-brator with reflectance of 15%, and 2.915 mm for ceramic plane calibrator with reflectance of 60%. The results show that when the optimal measurement distance and incident angle are selected, the reflectance of the calibrator has a great effect on the measurement results, regardless of the outlines or profiles. Based on the experiments, it is recommended to use the spherical calibrator or the standard plane with reflectance of around 18% as the standard, which can obtain the rea-sonable results. In addition, it is necessary to clearly provide the material category and surface reflectance information of the standard when calibrating the scanner according to the measure-ment standard.
ARTICLE | doi:10.20944/preprints202201.0434.v1
Subject: Earth Sciences, Environmental Sciences Keywords: Terrestrial Laser Scanner; SAR; coastal environment; weather effect; surface roughness.
Online: 28 January 2022 (11:18:54 CET)
In the past years, our knowledge of coastal environments has been enriched by remotely sensed data. However, to successfully extract information from a combination of different sensors systems, it should be understood how these interact with the common coastal environment. In this research we co-analyze two sensor systems: Terrestrial Laser Scanning (TLS) and satellite based Synthetic Aperture Radar (SAR). TLS shows large potential for examining coastal processes thanks to the possibility to retrieve repeated, accurate and dense topographic information in a rapid and non-invasive manner. However, TLS presents some limits due to its high economic costs and limited field of view. SAR systems are among the most used active remote sensor system for Earth Observation. Despite their relatively low resolution, SAR systems provide the ability to monitor and map coastal areas with complete, repeated and frequent coverage, penetrating through clouds and providing all weather monitoring. Moreover, Sentinel-1 SAR images are freely available. The availability of a permanently installed TLS system (PLS, Permanent Laser Scanner) allows us, to extensively compare Sentinel-1 SAR data and topographic laser scans during different conditions on a sandy beach. PLS data are compared with simultaneous Sentinel-1 SAR images in order to investigate the combined use of PLS and SAR in coastal environments. The purpose of this comparison is the investigation of a possible relation between PLS and SAR data: knowing their relation, SAR dataset could be correlated to beaches characteristics. Meteorological and surface roughness have also been taken into consideration in the evaluation of the correlation between PLS and SAR data. The permanently installed laser scanner for the present study is located in Noordwijk (the Netherlands). A generally positive but low correlation exists between the two variables. When considering weather phenomena, their correlation increases and shows a dependence on wind directions and speed. The correlation with the surface roughness, evaluated in terms of root-mean squared height, also depends on specific wind speed and directions.