Design of a Pulsed-Terahertz Photoconductive Antenna for Spectroscopy Applications

Abstract

In this paper, a photoconductive antenna (PCA) is designed and simulated which has some influential characteristics for spectroscopy of biological tissues. Firstly, the designed antenna has a broadband characteristic and can sweep from 0.3 THz to more than 2 THz. As the second feature, the circular polarization of this terahertz emitter can be useful in analyzing birefringence tissues that have different responses for linear and circular polarizations. For this purpose, a log-spiral metal strip is laid down on a GaAs substrate, which is then fed by a bowtie antenna. Meanwhile, modelling optic and electromagnetic physics in one package has certain difficulties, so laser beam illumination is modelled by COMSOL primarily for photocurrent generated between electrodes. Afterwards, calculated photocurrent has been imported to CST package as the excitation current. In addition, a dielectric lens is put on the back of the semiconductor substrate to increase the gain and consequently the efficiency of terahertz emitter. Finally, for the purpose of the reduction in the amplitude of noisy echoes, an anti-echo layer is located between substrate and lens that increases severely the optic-to-terahertz conversion rate of terahertz system.