Physical Sciences

Abstract: Purpose: To classify optical filters with different filtering levels according to their algorithmic complexity and to evaluate their effects on visual acuity (VA). The Block Decomposition Method (BDM) was applied to classify optical filters based on their estimated algorithmic complexity. Methods: VA was measured in all participants. Optical filters were analyzed using conventional statistical methods together with the BDM to characterize their algorithmic complexity. Results: Selective absorption filters exhibited a progressive reduction in transmittance within the blue spectral region (380–500 nm), accompanied by a shift of the cutoff wavelength toward longer wavelengths and a reduction in effective bandwidth, while maintaining relatively stable overall visible transmittance. Shannon entropy analysis revealed a progressive increase in statistical diversity as filter treatment time increased. In contrast, the algorithmic complexity estimated using the BDM exhibited a non-linear behavior, reaching its highest values in filters treated for 1 and 2 minutes. VA analysis performed on 235 eyes showed that the algorithmic complexity of visual responses depended on the visual function evaluated. Resolution acuity exhibited a decreasing trend in the estimated algorithmic complexity of its computational representation, whereas alignment acuity showed an overall increase across filter conditions. Detection acuity displayed non-linear changes, while recognition acuity included the highest individual nBDM value among the visual functions evaluated. Conclusions: Algorithmic complexity provides a complementary approach to conventional statistical methods for the analysis of ophthalmic filters and visual responses. The results indicate that statistical diversity and estimated algorithmic complexity characterize distinct and complementary properties of the computational representations analyzed. Selective absorption filters were associated with changes in the computational organization of the transmittance spectra and with differences in the computational representations of visual responses. BDM provided information about algorithmic organization that was complementary to conventional descriptive statistics and Shannon entropy, supporting its potential use as an additional computational tool for the characterization of photoselective filters and their relationship with visual performance.

Abstract: Subsurface ultrafast excitation of a transparent or\( \beta^{(K)} \) semitransparent solid requires two conditions that compete during propagation: nonlinear refraction must become strong enough to concentrate the field, while multiphoton absorption must remain weak enough that the pulse is not depleted before reaching the target. We formulate this competition in terms of characteristic Kerr and multiphoton-depletion lengths and use silicon as a quantitative test case. In a single-gap energetic approximation, the threshold of a \( K \)-photon interband channel occurs near \( \lambda_K^{(0)}=Khc/E_g \); the reduced coordinate \( x=\lambda E_g/hc \) therefore provides a material-independent way to organize where the lowest energetically allowed absorption order changes. These nominal thresholds do not determine an optimum on their own: phonon assistance, excitonic and multiband structure, and the measured wavelength dependence of \( n_2 \) and \( \beta^{(K)} \) control the actual response. The nonlinear figure of merit (NFOM) satisfies \( L_{\rm MPA}/L_{\rm Kerr}=2\pi\,\mathrm{NFOM} \). At any candidate operating intensity, simultaneous Kerr engagement and limited nonlinear depletion require the pointwise condition \( 2\pi\,\mathrm{NFOM}\gtrsim1 \); for a specified focusing length \( L_f \), the actual overlap is quantified by the interval \( I_{\rm eng}\le I\le I_{\rm dep} \). Using published silicon coefficients, representative \( L_f=100 \) and \( 250~\mu \)\( m \) values give the largest multiplicative operating-band widths near 1.95–2.15 \( \mu \)\( m \), no overlap at 2.55 \( \mu \)\( m \) within this reduced criterion, and narrower bands at 1.55 and 3.25 \( \mu \)\( m \). The calculation also shows why a low-intensity NFOM can greatly exaggerate the useful dynamic range once three-photon absorption becomes important at the operating intensity. Broadband wavelength, duration, energy, and focusing trends are calculated with a spectral UPPE implementation, while a generalized nonlinear Helmholtz equation solved by the finite-element method (NHE–FEM) provides the local scalar-nonparaxial description of strongly localized field–carrier dynamics. The combined framework connects nonlinear material coefficients, field evolution, photoexcited electron–hole carriers, and processing-relevant localization while explicitly separating the calculated electronic stage from subsequent lattice transformation.

Abstract: Compact, label-free optical transducers are attractive for real-time exhaled-breath screening. We report the characterization and classification performance of a low-power photonic elastic-backscatter sensing system (the Dr. T system) that interrogates injected gas mixtures with a 635 nm, <1 mW coherent diode-laser beam and records the back-scattered light on a two-dimensional silicon position-sensing detector (PSD) as a time series of intensity I and centroid coordinates (x, y) at 10 Hz. Seven calibration data sets were acquired in a sealed 0.11 L chamber—five disease-linked metabolite mixtures in a normal-air balance (CKD, SIBO, cystic fibrosis, COPD, heart disease), a healthy base-gas control, and an ambient control (19 records). Regression showed the beam-deflection axis (y vs x) to be a linear, reproducible common-mode signature of injection flow (slopes 0.18–0.24; R2 up to 0.98), whereas the optical response versus concentration (|I| vs C) is species-specific across a >20-fold slope range, constituting an optical fingerprint. A physically motivated feature space with Mahalanobis classification separated the four diseases carrying substantive metabolites at 100% leave-one-run-out recall; overall seven-class accuracy was 78.9%. Decisively, every substantive-metabolite disease was well separated from a base-gas control undergoing an identical chamber-pressure rise (D = 4.8–13.5), demonstrating that discrimination is driven by molecular optical signatures rather than common-mode pressure. The sensor can detect, discriminate, quantify and classify metabolite mixtures in vitro; signal-to-contrast enhancement for low-cross-section analytes, humidity compensation and radiometric calibration are identified as translation priorities.

Abstract: β2-Microglobulin (β2M) is an important biomarker associated with kidney dysfunction, dialysis-related amyloidosis, and inflammatory disorders, motivating the development of highly sensitive detection platforms. Here, we propose a nonlinear terahertz (THz) sensing platform based on graphene-enhanced third-harmonic generation (THG) for β2M detection. Unlike conventional graphene plasmonic sensors that rely on linear resonance shifts, the proposed approach exploits the strong dependence of graphene’s nonlinear optical response on its Fermi energy. Adsorption of charged β2M molecules alters graphene’s carrier concentration and Fermi energy, resulting in measurable changes in the THG response. The sensor consists of periodically patterned graphene micro-ribbons coupled to a gold substrate through a thin Kerr nonlinear dielectric spacer, forming a resonant metasurface with strong THz field confinement. The combined effects of graphene plasmonic resonances and cavity-enhanced field localization significantly enhance THG at relatively low incident intensities. The effects of graphene Fermi energy, dielectric thickness, and excitation intensity on the sensing performance are systematically investigated. The results demonstrate concentration-dependent shifts in the THG spectral response and intensity, with increasing β2M concentration producing a progressive shift toward higher frequencies. The proposed sensor detects β2M concentrations as low as 0.0001 g/L, achieving a sensitivity of 971 THz·L/g and a figure of merit (FOM) of 1706 L/g. These results demonstrate improved detection performance compared with conventional linear plasmonic sensing and highlight the potential of graphene-enhanced THG metasurfaces for sensitive, tunable, and compact THz biosensing and biomedical diagnostics.

Abstract: Integrated quantum photonics requires chip-scale biphoton sources, but phase matching, nonlinear coupling, loss, and spectral purity are coupled in high-index anisotropic waveguides. We present NanoPhotoNet-MPM, a physics-informed neural surrogate for modal spontaneous parametric down-conversion (SPDC) in monoclinic NbOCl₂ waveguides (d_22≈100 pm V^(-1)). The framework couples a DeepONet transverse eigensolver, regularised by the full-vectorial Helmholtz equations, with a quantum coupled-wave-equation propagator trained on 70 audited finite-difference eigenmode geometries. The trained model predicts a degenerate phase-matched crossing at w=283.13 nm and h=500.00 nm with an effective-index MAE of (4.16±0.75)×〖10〗^(-3), outperforming Gaussian process regression and plain multi-layer perceptron baselines by one to two orders of magnitude while guaranteeing wave-equation consistency. Joint spectral amplitude analysis at the degenerate design yields a heralded purity of P=0.122 (K=8.20), limited by symmetry-enforced group-velocity mismatch. A multi-mode genetic-algorithm search across Type-0, Type-I, and Type-II SPDC configurations identifies a Type-II design (m_p=4, m_s=0, m_i=1) at w=592.0 nm and h=270.0 nm that reaches P≈0.350 at L=0.5 mm with 95.9% idler survival under realistic propagation loss. The resulting framework is a generalizable surrogate-assisted design and active-learning guidance method for anisotropic van der Waals quantum photonic platforms.

Abstract: Computational Scattered Light Imaging (ComSLI) exploits the anisotropic scattering on aligned structures to reconstruct fiber networks in biological tissues, like the brain's nerve fiber network or the organization of collagen or muscle fibers. ComSLI discerns individual fiber pathways also in densely interwoven regions with multiple crossing fibers, achieves micrometer resolution across centimeter fields of view, is compatible with various sample preparations and staining, and only requires an LED light source and a camera, making it attractive for histological tissue analysis. However, while ComSLI precisely determines the 2D (in-plane) fiber orientations, determining the 3D (out-of-plane) fiber inclinations remained challenging due to missing a-priori knowledge of the inclination angles. In this study, we measured differently inclined 3D-nanoprinted fiber bundles with ComSLI, compared the resulting scattering patterns to those obtained from nerve fibers in a tilted brain section (vervet corpus callosum), and analyzed scattering signals in differently inclined brain regions. We show that the highest scattering intensity occurs along the same curved line as conical diffraction at an inclined grating. With this analytical model, we were able to estimate inclination angles with an accuracy of 3° or better. This finally allows to quantitatively determine fiber inclinations and reconstruct 3D fiber pathways with ComSLI.

Abstract: From smartphones to artificial intelligence chips, nearly all modern electronics depend on lithography to drive device miniaturization. Realizing nanoscale linewidths and fabricating intricate patterns remain central challenges for lithographic technologies. This work presents a novel multi-beam holography method capable of generating complex patterns for lithography. We demonstrate and systematically analyze the mechanism for the generation of sharp, complex bright fringes within an optical cavity equipped with phase-modulating elements. Through analysis of the types of split-amplitude interference and the position of the localized plane, two practical implementation schemes are established. For each scheme, we examine the key factors governing linewidth performance as well as its fundamental theoretical limits. Numerical simulations confirm the feasibility of our approach, yielding full-width at half-maximum (FWHM) values below 1/10 of the wavelength. Theoretical projections further suggest that linewidths narrower than 1/20 of the wavelength are attainable. Requiring only a highly compact optical arrangement, the proposed technique delivers both narrow-linewidth features and sophisticated patterns, highlighting its promise as an alternative lithographic platform.

Abstract: Transition-edge sensor (TES) microcalorimeters for future X-ray space observatories require accurate low-energy calibration, a regime where conventional X-ray sources are limited by intrinsic linewidth, count rate, or experimental complexity. In this work, we investigate fiber-coupled optical photons as a compact calibration tool for an Athena-like TES array. Optical pulses at 405 nm were generated with an acousto-optic modulator and delivered through an optical fiber onto a selected TES pixel inside a dilution refrigerator, via a dedicated cryogenic alignment interface. Externally triggered pulses were processed with an optimal-filter pipeline, including baseline subtraction, drift correction, and multi-Gaussian reconstruction of the pulse-height spectrum. The reconstructed spectra show resolved photon-number peaks consistent with the Poissonian statistics expected from an attenuated coherent source, reaching equivalent energies above 400 eV with a mean photon number exceeding 100 per pulse. The detector response was further tested for linearity by comparing the measured photon-number distributions against those predicted from the independently calibrated number of photons sent to the detector and a single, globally estimated detection efficiency, confirming Poissonian, linear behaviour across nearly two orders of magnitude in photon number. These results demonstrate that fiber-delivered optical photons can probe the few-eV to sub-keV response of Athena-like TES microcalorimeters, offering a practical and extensible framework for future low-energy calibration studies.

Abstract: Recent advances have broadened the capabilities of continuous-wave cavity ring-down spectroscopy (CW-CRDS), driven by demands for higher sensitivity, faster acquisition, and reliable operation in non-ideal environments. This review organizes progress through a taxonomy spanning: (i) cavity and coupling architectures, including compact resonators, related fiber-based systems, extended spectral implementations, and multiplexed or comb-enabled designs; (ii) ring-down acquisition and modulation approaches, from controlled and random cavity-length tuning to coding-based and hybrid modulation–absorption schemes, with different trade-offs in spectral coverage and drift sensitivity; and (iii) analysis workflows that address precision and traceability, such as Allan-variance–guided optimization, saturation/nonlinearity modeling, and uncertainty reporting. We connect these technical choices to key application areas, including trace-gas sensing, reactive and transient media, particulate/aerosol measurements, breath analysis, and precision spectroscopy. Deployment considerations, including sampling interfaces, long-term stability, and calibration transfer, are discussed for harsh or space-limited settings. Remaining challenges in mode matching, baseline control, scalable multiplexing, and low-power integration are outlined to guide next-generation CW-CRDS instruments.

Abstract: Achievable functionality of metasurfaces and metagratings strongly depends on the properties of the materials, of which their components are made. The key question is which loss level is still acceptable for a particular targeted functionality. In this study, it is numerically demonstrated that for meta-atoms of supercell-based metasurfaces with phase-gradient enabled functionality the loss level sets significant restrictions. Moreover, it pre-determines the range of geometrical-parameter variation needed to cover the entire phase range. For metagratings composed of equal meta-atoms, the loss related restrictions can be mitigated, provided that asymmetric diffractions are targeted. The examples are presented for THz range, for which conventional dielectrics and the (ultra-)high permittivity composites and unbiased ferroelectrics are considered as the candidate materials for metasurfaces and metagratings. The results directly demonstrate the effects exerted by the dielectric loss tangent, and the ones exerted by a selected geometrical parameter when the loss tangent is kept.

Abstract: Marine boundary-layer temperature inversions—warm air advecting over a cold sea surface—can bend near-horizontal light rays back toward the sea surface, forming an optical duct that dramatically alters the propagation of free-space optical (FSO) links over the ocean: ducted rays yield anomalous low-loss, over-the-horizon reception alongside strong multipath interference and scintillation. Although extensive inversion techniques exist for microwave evaporation ducts, no study to date has inverted optical duct parameters directly from optical channel observations. This paper presents, for the first time, a physics-informed deep learning framework that reconstructs the inversion-layer parameters—inversion gradient, layer-top height, and surface air temperature—from multi-wavelength FSO channel measurements. A forward model based on Bouguer ray tracing in a spherically stratified atmosphere (validated by split-step Fourier parabolic-equation analysis) generates the training dataset: thousands of inversion profiles sampled by Latin hypercube design, propagated at 850/1550 nm over 5–50 km maritime links, yielding receiver arrival angles, multipath structures, geometric focusing gains, and chromatic dispersion separations. A physics-guided neural network with residual learning—the refractivity gradient constraint embedded in the loss—inverts these observables into profile parameters. Numerical experiments demonstrate high-accuracy inversion of the inversion gradient, the parameter governing ducting (R² = 0.843, MAE = 0.033 K/m), with robustness to measurement noise. A systematic identifiability analysis further reveals that the layer-top height is weakly identifiable (R² = 0.22), whereas the surface air temperature is physically unobservable from link measurements—ray bending is effectively invariant under a uniform profile offset—and is thus supplied by a ground meteorological station, as in deployed FSO systems. The proposed framework establishes a new sensing dimension for maritime FSO channel prediction and duct-aware adaptive optical transmission systems.

Abstract: Multiparameter optical sensing of micrometer-sized particles requires morphological and material-related optical responses to be resolved for the same individual particles. Here, we develop a polarization-resolved digital holographic (PRDH) sensing system that integrates digital in-line holography with division-of-focal-plane polarimetry. The system numerically refocuses particles distributed at different axial positions and, for each resolved particle, retrieves three-dimensional coordinates, equivalent diameter, major and minor axes, perimeter, area, and shape factor, together with the linear Stokes parameters S0, S1, and S2 and the degree of linear polarization (DoLP). Particle-size measurements using three standard glass-microsphere groups yielded an average absolute relative deviation of approximately 5.5% between the group-mean measured diameters and the corresponding nominal values. For the particle groups investigated, the group-mean DoLP decreased with increasing nominal refractive index, whereas the comparison between 5 and 10 μm borosilicate microspheres indicated a comparatively weak size dependence. A descriptive linear fit to the five group means gives R2 = 0.926 over the investigated refractive-index range; this trend is further examined using T-matrix simulations, which show a qualitatively consistent refractive-index dependence in the forward-scattering region. The PRDH approach therefore provides particle-resolved, co-registered morphological and polarimetric information for multiparameter optical sensing of three-dimensional microparticle fields.

Abstract: Achieving high resolution imaging for a deployable space telescope requires segments co-phased to nanometer precision. Typical alignment uses point sources (distant stars) or extended ground scenes. An on-board active correction system has been developed to provide continuous alignment by using a fibre source instead. IMPACT (Image-based Mirror Phasing and Alignment using Convolutional neTworks) measures point spread functions (PSFs) on a secondary mirror detector separated from the main science camera. By applying a deep machine learning algorithm, piston and tip/tilt aberrations can be retrieved and corrected for. When simulated from a uniform distribution, PSF images were corrected from a mean Strehl of 0.18 to 0.99 after two model passes, reducing RMS errors from a mean of 276.7 nm down to 11.1 nm.

Abstract: Parity-time (\( \mathcal{PT} \)) symmetry offers a well-established route for enhancing light-matter interaction by means of formation of exceptional points. The model of plane waves is commonly used for finding and investigating exceptional points in open multilayer systems. Here we study behaviors of Bessel light beams in PT-symmetric multilayer structures. We adopt the method of scattering matrices to non-paraxial Bessel beams and determine positions of exceptional points depending on the transverse wave number and non-Hermiticity parameter for both propagating and evanescent beams. We reveal the evolution of exceptional and diabolic lines when the number of layers changes and find their link to the transmission and reflection spectra. This research may pave the avenue for exploiting light beams in non-Hermitian photonics.

Abstract: We present a novel deep learning-based technique for measuring linear-chirp instability of ultrashort laser pulse trains directly from their Frequency-Resolved Optical Gating (FROG) traces. This approach requires neither an iterative retrieval algorithm nor pre- or post-processing steps, enabling real-time measurements. Although our proof-of-concept convolutional neural networks (CNNs) are moderately deep and trained on compact datasets, they demonstrate resilience to significant additive noise (up to 14%) and high robustness across a wide range of laser pulse parameter variations. When tested on unseen data, our classification network (ICN-1) achieved an accuracy of 80.0% (with an off-by-one accuracy of 100.0%), and our regression network (IRN-2) yielded a normalized root-mean-square error (NRMSE) of 10.2%.

Abstract: Fulgides are a class of organic compounds that have been extensively investigated because of their photochromic properties and the wide range of applications arising from them. Fulgimides, an important subclass of fulgides, contain a succinimide moiety in place of the succinic anhydride functionality found in fulgides. Isofulgimides are constitutional isomers of fulgimides in which the succinimide ring is replaced by a 5-iminodihydrofuran-2(3H)-one moiety. Although isofulgimides also exhibit photochromism, their synthesis and photochromic behavior have received considerably less attention than those of other fulgide derivatives. Reports on isofulgimides remain scarce, and crystallographic investigations are particularly limited. As part of our ongoing efforts to develop novel photochromic compounds, we synthesized a unique dimeric isofulgimide featuring an N–N single-bond linkage. Herein, we report its synthesis, crystal structure, and photochromic properties.

Abstract: Thermodynamic reasoning has entered nonlinear optics along three routes—wave-turbulence kinetics, the equilibrium thermodynamics of highly multimoded systems, and the statistical mechanics of mode locking—but in each the modal basis or coarse-graining cutoff is specified externally, by a waveguide, a spectral window, or a cavity bandwidth. This review asks what survives when the object is a strongly chirped dissipative soliton of the complex cubic–quintic Ginzburg–Landau equation, a structure that exists only because energy flows through it. The mechanism that localizes such a pulse also bounds its spectrum, separating the correlation function into a graining scale set by the spectral cutoff and a collective scale set by the spectral core. Their ratio is selected by the dynamics rather than imposed, and closed-form adiabatic spectra in both dispersion regimes compress the parameter space onto a single master diagram carrying a shape entropy, an internal energy, and a continuation-dependent energy–entropy slope. Dissipative soliton resonance is read as spectral core narrowing, intrinsic in normal dispersion and conditional in anomalous dispersion. We state precisely where the borrowed vocabulary becomes strained: a deterministic pulse remains first-order coherent, so the scale ratio is not yet a count of statistical degrees of freedom, and the promotion requires an ensemble-coherence calibration that is specified but not assumed. The result is a falsifiable framework for dissipative-soliton coherence, energy scaling, and stability, with experimental signatures and design criteria for chirped-pulse oscillators.

Abstract: Heavy metal fluoride glasses (HMFGs), particularly fluorozirconate glass systems such as ZBLAN have attracted considerable attention due to their unique physical properties, including low phonon energies, wide transparency from the UV to the mid-IR, and high rare-earth ion doping solubility, making them promising materials for photonic applications. This review provides an overview of fluoride glass synthesis methods, structural characteristics, and physical properties of fluorozirconate glasses, with emphasis on glass processing conditions, thermal, mechanical, and optical properties. The structural characteristics are discussed in terms of zirconium–fluorine polyhedral networks and their compositional dependence, while physical properties are analyzed, including glass transition behavior, crystallization tendency, elastic moduli, and infrared transmission. Rare-earth doped Er3+, Ho3+, and Tm3+ ZBLAN glasses are also discussed, which exhibit efficient emissions in the near and mid-IR spectral regions. Although significant progress has been achieved, limitations related to thermal stability, mechanical strength, and incomplete understanding of structure–property relationships persist. Future research should therefore focus on compositional optimization and predictive structural modeling to enable the design of improved fluoride glasses for various applications.

Abstract: We simulate the propagation of a single photon propagating within a modal group, traversing through a multimode optical fiber in the presence of mode coupling. We illustrate the propagation graphically on a group of higher order Poincare spheres. The spheres display the propagation of the light within the modal group including polarization in time and in distance as the transmission proceeds. Thus, the amplitudes and the relative phases within the group can be visualized throughout the transmission, which is novel and very useful to understand the propagation. At the fiber output we show how to recover the input of a classical state using the simulated propagation information displayed on such multiple spheres. Once a classical - modal path is established from end to end, one can transmit quantum states, for example a spatial – time binned QKD (quantum key distribution) code. A quantum state follows this classical path. This can include binary or qudit information. Accessing a photon output state is important for many quantum network applications including quantum key distribution, routing and entanglement swapping. In addition, one can use other modal groups within the same fiber to multiplex other quantum channels. Further, one can multiplex within a modal group using principal modes, a more complicated communication method. Using the spheres, this situation is also discussed. Applications include higher dimensional quantum communications, quantum cryptography, and quantum networks. It is important to point out that in today’s commercial quantum communications systems, the quantum states are single photon states but not entangled. This includes both discrete and continuous variable quantum key distribution systems. In this report we are also looking at single photon systems but not entangled, unless stated otherwise.

Abstract: In laser phase transformation hardening and laser cladding processes, the inherent thermodynamic limitations of conventional intensity distributions severely restrict the uniformity of metallurgical reaction. Although programmable beam shaping devices offer flexibility in profile reconstruction, their transmissive structure results in a low laser-induced damage threshold (LIDT), making them unsuitable for long-term stable operation at kilowatt-level power. This study proposes a reflective freeform mirror design method based on the principle of zonal energy mapping. The method constructs energy mapping relations that correlate the irradiance distribution in every sub-region of the incident Gaussian beam with the desired M-shaped irradiance profile. Relying on such mappings, the local surface generatrices of all sub-regions are solved separately; these generatrices are subsequently assembled to yield an integrated mirror surface. Optical performance was verified through Zemax non-sequential ray tracing simulations. The mirror was precisely machined using single-point diamond turning (SPDT). The experimental results show that the measured intensity distribution on the observation screen exhibits a typical M-shaped profile, with a peak-to-valley ratio of 1.28, which is in good agreement with the design target. This method provides a technically feasible and engineering-robust solution for complex thermal flux control requirements in high-power laser material processing.