A quest of a new eye for terahertz-waves region

Progress in far-infrared and terahertz technology is reviewed since 1950 to the present. There are three ways of approach to this frontier region; optic, electronic or quantum electronic approach. This paper describes optic, i.e. grating and Fourier-transform spectroscopy, or quantum electronic, i.e. far-infrared lasers and terahertz time-domain spectroscopy/imaging (THz-TDS). Experimental results in far-infrared spectroscopy and in terahertz time-domain spectroscopy/imaging are shown.