ABSTRACT
This chapter discusses the experimental configurations used to generate the radiation, the basic physical mechanisms present in the lasers, and some spectroscopic features associated with the stronger emitting molecules. It reviews the characteristics of optically pumped mid-infrared and far-infrared lasers. Physically, the far-infrared (FIR) power increases with pressure at low pressures simply because the pump absorption increases. The major features of superradiance can be illustrated with the results of a simple model. Stimulated Raman emission in optically pumped FIR systems was first observed under pulsed pumping conditions. Polar polyatomic molecules generally have a number of infrared active vibrational modes in addition to rich microwave and far-infrared spectra. The methyl halides, particularly those containing fluorine and iodine, were among the first lasing species discovered. Ammonia and its isotopic derivatives have been pumped by isotopic CO2 lasers and N2O lasers. Heavy water is the most important molecule for pulsed FIR emission.
