An influence of the absolute phase of THz pulse on linear and nonlinear medium response

The influence of an absolute phase of the THz pulse with a few cycles on the spectrum and spectral dynamics of signal reflected from or transmitted through the explosive or paper sheet is analyzed for problems of the detection and identification of explosive. The signal was measured on the long-term interval with duration about 180 ps and contains both the main reflected THz pulse and the subpulse with less intensity. Two cases of the reflection (normal and specular reflection) of the THz pulse from the RDX are considered. For the THz pulse interaction with the paper sheet the transmission mode is analyzed. Dependence of the nonlinear response of substance from the absolute phase of pulse is illustrated by examples of SHG or self-action of laser pulse with a few cycles. We showed that the absolute phase of pulse plays one of the key roles for the detection and identification of the substances at the reflection mode. It is necessary to investigate this problem with big attention during next few years.