Time variant source resistance in the THz photoconductive antenna

Terahertz (THz) photoconductive antennas are the most common devices for the generation and detection of THz waves. One of the main problems of the current photoconductive antennas as the emitter is that the optical-THz conversion efficiency is very low, thus it is difficult to obtain high power THz radiation. Impedance mismatching between the antenna and the photoconductive material (which acts as the source impedance) is one of the primary factors on this low conversion efficiency. In order to assess this issue, proper evaluation of the resistance of the photoconductive material is required. In this paper, the time dependant conductivity of the photoconductive material based on pulsed system is first calculated. Then, through this conductivity, the source conductance (resistance) in THz photoconductive antenna is determined which illustrates influences of different parameters of laser pulses, photoconductive material properties and THz antenna. This new formula can aid in a better theoretical assessment as part of total optical-THz conversion efficiency calculation as the source conductance (resistance) can be more accurately derived.