Experimental and Computational Analysis of Broadband THz Photoconductive Antennas

The work presents the fabrication and measurements of four LT-GaAs photoconductive terahertz (THz) antennas with different geometries of metallic electrodes. The goal is to analyze the overall bandwidth of the antennas through a comparison between the spectra of the generated photocurrent in the antenna gap, the radiated electric field THz pulse, and the S-11 parameter of the metallic electrodes. The photocurrent density and the S-11 parameters are computed using COMSOL multiphysics, while the generated THz pulse was experimentally measured using a time-domain spectroscopy system. The polarizations of the photoconductive antennas are experimentally measured, using x-cut quartz crystal halfwave plates, showing polarization in the direction of the electrode's long axis. Pinholes are used to verify system alignment and quality of the radiated signal spectra. The results show that the spectra of the radiated THz pulses in all four antennas considered in this work are dominated by the behavior of the S-11 parameter at the lower part of the frequency band, but with the decreasing photocurrent dominating the spectra at higher frequencies.