Efficiency calculation of THz photoconductive antennas in a pulsed system

To design terahertz (THz) photoconductive antennas with high output power and/or high optical-THz conversion efficiency, the photoconductor property is an important consideration. In this paper, the effect of using approximate and precise source conductance equations on obtaining optical-THz conversion efficiency of the antenna is investigated. It is shown that based on these two equations, before the occurrence of saturation at high optical powers, the total optical-THz conversion efficiencies are different. This is due to the difference in matching between the source and the antenna. Moreover, optimum optical-THz conversion efficiency in relation to input optical power and limiting parameters on radiated THz power are addressed. This analysis provides information on tuning the system for the suitable input optical power; hence optimum optical-THz conversion efficiencies can be obtained from the device. Furthermore, the efficiency expression derived in [1] is further modified using the new source conductance definition and equivalent circuit method, the results obtained using the improved expression better match with experiment results reported in literature.