Coherent detection of terahertz pulses based on two-photon absorption in a photodiode

Abstract

The authors present a simple and robust method for the measurement of the terahertz-induced lensing effect that may be used for the coherent detection of few-cycle terahertz pulses. It is based on two-photon absorption of a 1.5μm probe pulse in a standard silicon photodiode. The change in the spatial probe pulse profile caused by terahertz-induced lensing leads to a variation of the diode signal that is induced by two-photon absorption even though the total pulse energy has remained constant. This variation is shown to be proportional to the terahertz electric field.