Optical properties of thin-film absorbing capacitive periodic structures in the terahertz range

Thin conductive films deposited on the surface of the heat-sensitive element of the radiation receiver make it possible to absorb up to 50% of the incident radiation. This increases the efficacy of detectors in the terahertz (THz) frequency range. The absorbing conductive coating on the array of a multi-pixel detector is an ordered structure with dimensions comparable to the wavelength of THz radiation. Diffraction of radiation on this structure leads to a change in the wavefront of both transmitted and reflected waves, leading to image distortion in a multi-pixel detector. Based on experimental data obtained using pulsed THz and IR Fourier spectroscopy, the transmission and conductivity spectra of solid films and capacitive Al meshes of different thicknesses were analyzed. The optimal thickness of the Al coating for maximum absorption of THz radiation has been determined. The transmission spectra of capacitive grids with an Al film thickness corresponding to the maximum absorption indicate the disappearance of diffraction effects in the THz range.