Generation of coherent far-infrared radiation using lasers

The methods surveyed include the isolation of the frequency difference between two lasers, SRS by polaritons, the optical pumping of gases, and the development of the electrical-discharge laser. Attention is also given to the principles underlying these methods. The properties of the working media, that is, the nonlinear properties of crystal converters, are described. An analysis is then made of methods for producing inversion of level populations in gases used in lasers (pumped optically or by an electrical discharge). Designs for the far infrared are considered, along with the performance expected from them.