The generation and frequency measurement of short-wavelength far-infrared laser emissions

A significantly improved three-laser heterodyne system has been assembled to generate and measure short-wavelength far-infrared (FIR) laser emissions. Over the past several years, this system has been used to discover fifty-five FIR laser emissions, ranging in wavelength from 26.3 to 185.0 μm. These emissions were generated by optically pumping a FIR cavity with a continuous-wave carbon dioxide laser in a X-V geometry when using either hydrazine or a methanol isotopologue as the FIR laser medium. Although heterodyne techniques can be used to measure the frequencies of these FIR laser emissions with fractional uncertainties of ±2×10^-7, shortcomings in the previous system limited its effectiveness. Improvements made to the three-laser heterodyne system have resulted in an increase in the spectral range used to search for the beat between the known and unknown laser frequencies (an increase of up to 25 GHz) as well as an increase in the system´s sensitivity (by up to a factor of 30), all without requiring the use of an additional microwave frequency source. With this improved system, the FIR laser frequencies for the recently discovered 53.9- and 90.0-μm laser emissions generated by optically pumped CH₃OD have been measured.