Experimental determination of the zero value of the phase characteristic of an active medium in a ring laser emitting at λ = 3.39 μ

An investigation was made of a resonance effect in a gas ring laser, which gave rise to a power peak in the opposite waves. The center of the peak corresponded to the zero value of the phase characteristic associated with the nonlinear dispersion of the medium. The theory of the effect and the results of the experiments carried out at λ = 3.39 μ were analyzed. A "methane" peak was used to measure the frequency shift of the center of the power peak relative to the center of the methane transition as a function of pressure in a helium-neon mixture.