Transmission measurements using THz time-domain spectroscopy (THz-TDS) are often affected by amplitude and phase changes due to spatial properties of the focused beam. This axial anomaly is called the complex Gouy phase and significantly influences measurements as well as determination of material parameters of a measured sample. The method of the Gouy phase shift compensation has been published in our previous paper . In this paper, we suggest a model of spatial-frequency dependence of the complex phase with additional effects of non-axial components due to focusing on a finite size detector.
In this paper we apply the terahertz time-domain spectroscopy (THz-TDS) to obtain optical function spectra in the range from 0.06 to 3 THz. Polarization sensitivity is obtained using azimuth-controlled wire-grid polarizers. We demonstrate general methods on characterization of plasmonic semiconductors. Detail characterization of optical and magneto-optical material properties is also motivated by a need of optical isolator in THz spectral range. The technique is applied to III-V semiconductors. The typical material is a single crystal undoped InSb having the plasma frequency in the range of interest. With appropriate magnetic field (in our case 0.4 T) we observed coupling of plasma and cyclotron behavior of free electrons with gigantic magneto-optic effect in the THz spectral range.