Significant enhancement of THz detectivity by lowering ZnTe crystal temperature in electro-optic sampling

Abstract

The temperature of the ZnTe detection crystal in a THz time-domain system was tuned continuously from 300 K to 1.5 K to minimize phonon absorption, thus enhance its detectivity. The THz peak amplitude was observed to increase more than 10 times. To explain this phenomenon, the THz transmission spectra of the ZnTe crystal at different temperatures were also measured, and the refractive index and absorption coefficient of the crystal were extracted. The experiments and theoretic analysis reveal that the significant detectivity enhancement is due to the reduced absorption of the THz field and phase matching change in the detection crystal with temperature decreasing, which makes the ZnTe crystal suitable for integrating with cryogenic applications.