A quantitative analysis of the lock-in phase difference in terahertz time-domain spectroscopy

In terahertz time-domain spectroscopy (THz-TDS), the THz electric field strength is generally characterized by the photocurrent of the THz receiver, which is extracted from the in-phase component output of lock-in amplifier (LIA) in the system. As to LIA, the in-phase output is directly influenced by the phase difference between the voltage/current input (the signal of THz receiver) and the reference signal. Since the changing of phase difference during testing the sample is often ignored in the experiments, a quantitative and rounded analysis of the effect on the result is presented in this paper to provide a go-to source for the researchers who are interested in this issue.