The time-domain THz spectroscopy (TDS) is a unique technique of spectroscopic studies that has been rapidly developing in the recent years, which was stimulated by wide practical applications for biomedical diagnostics, creation of up-to-date safety systems, control of pharmacological products, and so on. This technique is based on the use of short (picosecond) terahertz pulses and, in contrast to the classical spectroscopy, does not require frequency scanning. TDS records directly an oscillogram of the terahertz pulse that has passed through the sample. As a result both the amplitude and phase spectra are obtained in a wide frequency range.