ИСТИНА

We study the spectral features of a THz pulse transmitted through/reflected from a substance covered by a disordered structure by means of computer simulation. It is known that in real conditions the THz TDS results undergo various distortions, for example, because substance under investigation can be put into covering. Often as a result, the reflected/transmitted pulse spectra transform essentially and thus, one may reveal additional absorption frequencies, which can be identified as belonging to a dangerous substance. Moreover, studying the reflected/transmitted spectra of a broadband THz pulse interacting with a medium, we may observe a broadening of these spectra due to the cascade mechanism of higher level excitation as it was shown by us recently. In this report we study the influence of the pulse duration on this mechanism appearence.