Analysis of terahertz radiation under nonlinear mode of photoconductive switches

Abstract

Terahertz electromagnetic radiation has been generated successfully with semi-insulating Gallium Arsenide(GaAs) photoconductive switches in linear mode, but haven't detected any radiation under nonlinear mode of photoconductive antenna. Nevertheless, compared with linear mode, the photoconductive switches in the mode of nonlinear has a sharper current rise. In this condition, the possibility of generating terahertz wave via the mode of nonlinear of photoconductive switches has discussed. We based on Drude-Lorentz theory and optically activated domain theory of nonlinear mode of photoconductive antenna, instantaneous response of photoexcited carriers in the mode of nonlinear is analyzed, and carrier dynamic characteristic connected with terahertz radiation in semi-insulating GaAs is discussed. The amplitude of THz radiation originating from impact ionization and acceleration in domain electric field is calculated. According to theory of far field radiation of terahertz wave, it can arrived at that the electric field intensity of far field of THz wave has a direct proportion to the derivative of current density in photoconductive antenna. For reason given above, the intensity of single THz wave with single triggering under the mode of nonlinear stronger than intensity of linear mode can be derived.