Polarization-dependent efficiency of photoconducting THz transmitters and receivers

The emission and detection efficiencies of photoconducting THz transmitters and receivers are found to be sensitive to the polarization of the optical gating pulse. Signal amplitudes from GaAs coplanar stripline transmitters and silicon-on-sapphire dipole receivers vary by factors of up to 4 and 3, respectively, with rotation of the exciting pulse polarization. In both cases, maximum signal is obtained when the polarization of the normally incident light is perpendicular to the edge of the metal electrodes. This polarization sensitivity, which appears to arise from differences in the spatial distribution of photoexcited carriers in the semiconductor, needs to be considered when optimizing the signal-to-noise ratio in coherent THz spectroscopy. (C) 1998 American Institute of Physics.