High Speed Single Point THz Phase Measurement Based on Dual Channel Lock-in Technique

The generation of radiation in the range of hundreds of GHz with electronic systems is challenging. Using photonic systems makes it possible to generate and detect signals in the complete frequency range. To measure amplitude and phase with so-called time domain spectroscopy (TDS) systems usually requires the acquisition and Fourier analysis of complete pulse transients. Simplifying this process helps to design systems which allow for fast scanning in the THz range. We modified a commercial TDS system with a two-channel lock-in amplifier and a bandpass filter in the range of 800-900GHz to completely remove the post processing which is necessary to acquire phase and amplitude information. In this paper we present a system which reduces the acquired data to two output parameters for amplitude and phase which can be measured at the same time. This makes precise and fast measurements of phase objects at a target frequency possible. This is shown by acquiring a qualitative phase image of a technical sample.