Terahertz waves: a tool for condensed matter, the life sciences and astronomy

In the wide range of the electromagnetic wave spectrum, the terahertz (THz) frequency region has for a long time been an unexplored region and its technological development has been left behind. Nowadays, however, science and technology based on THz electromagnetic waves have been increasingly progressing and are still growing. In the THz region, both features of wave' and light' appear, enabling the manipulation of the THz wave from both approaches of electronics and optics/photonics. From the viewpoint of research targets, THz technology is expected to be the key for unlocking mysteries behind quantum effects in condensed-matter physics, life activities in biology, and the birth of the celestial bodies in astronomy. In addition to such fundamental sciences, THz spectroscopy and imaging can be used as a powerful tool for nondestructive remote inspection in industrial and medical fields. In this article I review cutting-edge technologies of THz sensing, imaging and spectroscopy, and describe how effectively the THz measurements are applied to various researches.