MODE STRUCTURE OF HOLLOW DIELECTRIC WAVE-GUIDE LASERS

The mode structure of hollow dielectric waveguide lasers with free space sections and flat mirrors is studied theoretically and experimentally. The study covers the fundamental mode and the three most important higher order modes, and graphs are given which identify regions of high mode discrimination in the parameter space. Calculated coupling losses are verified experimentally by detailed studies of the output power of CO2 lasers as a function of resonator geometry. The intensity profile inside and outside the resonator is calculated, and the profile outside the resonator is compared with experiments for the fundamental mode as well as for the higher order modes. It is shown that in general the fundamental mode is non-Gaussian, and that drastically different output characteristics are obtained for different choice of output plane. The paper identifies design criteria for obtaining single line and single mode oscillation over a wide tuning range, even in the densest region of the CO2 laser line spectrum, and this is exemplified by a spectroscopic application. © 1990 Springer-Verlag.