Terahertz Spectroscopy and Applications

There has been a long and intimate relationship between frequency measurement and spectroscopy. For a time, wavelength based optical measurements and frequency based microwave measurements provided a measure of the speed of light. While as fundamental references these have been eclipsed by exquisite modern atomic measurements, frequency measurement and control still play a vital role in the terahertz (a.k.a. submillimeter) spectral region and are an important part of its rapidly developing technology. This paper is primarily from a terahertz (a.k.a. submillimeter) perspective and focus on the science and technology that has resulted. This includes discussions of the frequency chain that passes through the terahertz, as well as of the astronomy, atmospheric science, remote sensing, analytical chemistry, and imaging that reside there