Calculation of the waveguide probe for terahertz spectroscopy of a layered medium

Using the Kirchhoff approximation, an analytical solution of the diffraction problem on finding the spectra of the amplitudes of the modes of a waveguide probe at reflection of a terahertz pulse from the open end of a hollow core waveguide contacting with a layered medium, is obtained. On example of the electrodynamic model of the skin as two layers of an aqueous albumin solution excited by the modes of a hollow metal waveguide, the effect of epidermal humidity on the spectra of amplitudes of reflected waveguide modes, which can be measured using the time domain spectroscopy, is studied. It is established that the optimal choice of the frequency range refers to single-mode regime of the waveguide work.