Influence of Gouy Phase Shift on THz Time-Domain Spectroscopy

In THz-TDS, THz radiations have to be transformed generally to be focused on the sample. However, the THz frequency spectrum and temporal waveforms may be changed by Gouy phase shift in the focus . The Gouy phase shift is the well known pi phase shift with respect to a plane wave as a focused electromagnetic beam propagates through its focus . As we know, most of researches in relation to the interaction between the focused light and media still consider the light beam in the vicinity of the focus as plane wave, and ignore the phase singularities which could lead to the superluminal velocities . Here, we study the influence of Gouy phase shift on the THz-TDS by means of numerical calculation and corresponding experiments.