The influence of Ne isotopes on the single mode operation of He-Ne and He-Ne/I/sub 2/ lasers

When using He-Ne lasers in our experiments, we observed that two adjacent longitudinal modes with the same polarization operate simultaneously with steady output power for each mode when the frequency spacing between them is several times lower than the homogeneous linewidth of the laser transition. In the case of a mixture of /sup 20/Ne and /sup 22/Ne isotopes, an analytical expression for the output power is obtained and calculated for parameters close to the experimental conditions. The theoretical predictions are in agreement with the experimental results. The theory also shows that in the case of pure neon isotope the competition between the longitudinal modes is stronger than in the case of neon isotopes mixture. It is proposed to improve the single mode selection efficiency for He-Ne and He-Ne/I/sub 2/ lasers and to enhance their single-mode output power using pure neon isotopes.