Generation and detection of terahertz pulsed radiation with photoconductive antennas and its application to imaging

We describe the basic properties of photoconductive (PC) antennas as emitters and detectors of terahertz (THz) pulsed radiation. The efficiency of PC antennas is discussed, taking into account the saturation effect due to field screening by photo-generated carriers. We show that maximum emission efficiency under a constant pump power condition is achieved by adjusting the PC gap size so that the pump intensity (power divided by PC area) is equal to the characteristic saturation intensity. We also discuss the bandwidth of PC antennas and conclude that PC antennas are capable of generating and detecting ultra-broad THz radiation beyond 10 THz when short enough laser pulses are used. Our conclusion is demonstrated experimentally by detecting ultra-broadband THz radiation, whose spectrum distributed up to 40 THz, with a PC antenna. As an example of applications of THz pulsed radiation based on a PC emitter-detector system, results for the imaging of objects in powders are presented and discussed.