Distortion analysis of pulsed terahertz signal measured with spectral-encoding technique

Abstract

The principle of the spectral-encoding technique, one of the single-shot techniques for measurement of arbitrary pulsed terahertz (THz) signals, or T-rays, is demonstrated theoretically and through simulation. For single-cycle input THz pulse (bipolar wave form), THz signal could be retrieved faithfully under certain conditions, while for the multicycle input case, the THz signal cannot be retrieved without any distortion. However, there is an optimal length of the chirped-probe-pulse, corresponding to the characteristic time of the multicycle THz field, to minimize the distortion in the retrieved THz signal. Three main possible sources of distortions from both bipolar and multicycle THz signals are analyzed systematically. The first distortion originates from the mismatch of the optimal duration Tco of the chirped-probe-pulse and the T-ray length T. The second one is relevant to the spectrum bandwidth of the probe pulse. The third one occurs when the modulation depth k⪡1 is not satisfied. It comes from the neglect of the quadratic term of the modulation depth k, which reflects the strength of the THz signal in the retrieving process. Possible strategies are proposed to reduce these distortions.