Modulation techniques for submillimeter lasers

It is noted that optically pumped molecular gas lasers yield a great number (approximately 1000) of emission lines in the region between 200 GHz and 8 THz and that phase stabilization of these sources with respect to a coherent reference signal, obtained through frequency synthesis, is very important from a metrological point of view and may prove useful in spectroscopical work and in special types of communication systems. The importance of developing methods of fast frequency modulation for these lasers is stressed. It is shown, both theoretically and on the basis of experimental work, that an adequate modulation for phase stabilization is feasible either by injection locking or by pulling the laser cavity through a suitable coupled reactance. Various coupling problems of the optical beams are also examined theoretically and experimentally in order to evaluate the efficiency of the methods described.