Spectroscopy by pulsed terahertz radiation

Spectroscopies using terahertz (THz) radiation excited by ultrashort laser pulses have been rapidly developing recently. In this paper, the principles of various types of THz time domain spectroscopies (THz TDSs), i.e. transmission-, reflection- and ellipsometry-type THz TDSs, and their applications to the characterization of semiconductors are described. In addition to the THz TDS using a femtosecond laser, a sub-THz TDS system using a cheap and compact continuous multimode laser diode is also described.