ABSTRACT
Terahertz (THz) waves, also called T-rays, refer to electromagnetic radiation in the frequency range of 0.1-10 THz-one terahertz, abbreviated as THz, representing 1012 Hz. In the electromagnetic spectrum, THz waves occupy the region between microwaves and the infrared, as shown in Figure 1.1. Until about two decades ago, when THz time-domain spectroscopy technique was invented by Grischkowsky and his colleagues (Fattinger and Grischkowsky 1988, 1989; van Exter et al. 1989), the THz spectrum had remained more or less unexplored and unutilized. However, the development of ultrafast lasers (Son et al. 1992; Spence et al. 1991; Valdmanis and Fork 1986) and derivative techniques such as photoconductive switching and sampling (Auston et al. 1984; Ketchen et al. 1986; Mourou et al. 1981a,b; Smith et al. 1981) and electro-optic generation and detection (Auston et al. 1984; Valdmanis et al. 1982) in the 1980s made it feasible to study the THz waves. In other words, ultrafast technology helped develop ecient THz sources and detectors, though the fabrication of compact THz system is still a challenge.
