Spatio-temporal carrier dynamics in photoconductive switches

Summary form only given.We present the first experiments which directly visualize the spatial pattern formed by carriers in a photoconductive switch under the action of an electric bias field. These experiments lay the groundwork for further optimization of photoconductive switches as THz emitters or ultrafast photodetectors. This is because the spatial average over the motion of electrons and holes determines the properties of the current pulses and the subsequent impulsive THz radiation generated in the switch by femtosecond optical excitation. Our data demonstrate different electron-hole separations in the center and close to the edges of the non-uniform Gaussian carrier distribution created by the excitation laser pulses. A simple model assuming density dependent screening qualitatively reproduces the complicated experimental patterns.