Introduction

For a broader view: De Lucia, F. C. Science and Technology in the Submillimeter Region‚. Opt. Photonics News 14, 44-50 (2003).‚

The genesis of microwave, and ultimately THz spectroscopy, was the war time development of microwave radar. However, this development was greatly aided by a fortuitous (for microwave spectroscopy at least!) accident that placed a previously unknown transition of water (the 616-523 at 22 GHz) in the middle of the spectral region that was being developed at the end of the war as the next new radar band. Not only did this make vast quantities of sophisticated equipment that ordinarily would have been beyond the means of university researchers immediately available, but it also established the 'relevance' of the field.

By 1948 the field was mature enough that an article in Reviews of Modern Physics [1]. This drive toward ever higher frequencies was aided by the rapidly increasing absorption strengths of the spectra of many of the most important small fundamental molecules (e.g. H2O, O2, CO, HCl, and O3) which lay there.

A strong argument can be made that this scientific focus led spectroscopists towards the development of practical and robust ‘THz’ technologies, including the crossed waveguide harmonic generator [4].

While microwave spectroscopy had a number of other streams, in the end this drive to higher frequency to observe the most fundamental species provided the enduring legacy for the field. Because these small species were not only scientifically fundamental but also pervasive in many physical and chemical systems, the strong interactions in the THz region have led to a number of important applications. In later sections we will discuss some of them. At appropriate places links are included to particularly useful web sites which can be consulted for additional information.

References

  1. Gordy, W. Microwave Spectroscopy Rev. Mod. Phys. 20, 668-717 (1948). Google Scholar
  2. Gordy, W. Microwave Spectroscopy above 60 KMc Ann. N. Y. Acad. Sci. 55, 744-788 (1952). Google Scholar
  3. Burrus, C. A. & Gordy, W. Submillimeter Wave Spectroscopy Phys. Rev. 93, 897-898 (1954). Google Scholar
  4. King, W. C. & Gordy, W. One to Two Millimeter Wave Spectroscopy. I Phys. Rev. 90, 319-320 (1953). Google Scholar
  5. Unterberger, R. R. & Smith, W. V. A Microwave Secondary Frequency Standard Rev. Sci. Instrum. 19, 580-585 (1948). Google Scholar
  6. Helminger, P., De Lucia, F. C. & Gordy, W. Extension of Microwave Absorption Spectroscopy to 0.37-mm Wavelength Phys. Rev. Lett. 25, 1397-1399 (1970). Google Scholar