Terahertz research - the first thirty years (1895-1924)

In a very recent publication the author was amused to read ... 'that this region of the spectrum has only begun to be explored thoroughly over the last decade'. The authors might be surprised to learn that there were over 1500 publications concerning what is now conveniently called the terahertz (THz) region between the 1890s and 1970. There were countless more in the next 25 years. However, rather than dwelling on the well-documented surge of activity from the late 1950s onwards, due to such things as the arrival of digital computers for Fourier transform spectroscopy, helium-cooled detectors and long-wavelength lasers, this paper looks back to the very early years of research in this spectral region. The end date of 1923 is the year when the 'gap' between the far-infrared and electric waves (as they were then called) was closed. It is truly remarkable that so much was achieved with what was very basic technology.