Continuous-Wave Terahertz Digital Holography Based on a Hollow Waveguide

The major challenge limiting the application of terahertz(THz) technology lies in the significant attenuation of THz waves loss of THz waves during free-space transmission arising from water vapor absorption and gas molecule scattering. Compared with free space propagation, low-loss and stable transmission of THz wave can be achieved through the waveguide. Waveguide transmission at low THz frequencies has attracted considerable attention, particularly at around 300 GHz (0.3 THz). Among the various types of THz waveguides, hollow waveguides offer a simple structure, ease of fabrication, low cost, and excellent transmission performance in the THz regime. Here, we design and fabricate a low-loss THz metal dielectric hollow waveguide based on polypropylene (PP) tubing, where an external silver film coated on the PP tube forms a leaky-type hollow waveguide structure. The linear transmission loss is measured to be 1.35 dB/m at 300 GHz. By optimizing this low-loss THz hollow waveguide, we achieve a far-field THz digital holographic (TDH) imaging recording configuration for the first time. To evaluate the imaging performance, different types of samples are measured. Experimental results for a plastic plate with aluminum strips validate a lateral resolution of ∼2.5 mm. The proposed method holds potential as a powerful tool for investigating spontaneous phenomena in the THz band.