Investigation of back reflections in a ring laser

An experimental investigation was made of the influence of back reflections (scattering), due to the presence of inhomogeneities in the optical elements of the resonator, on the difference frequency of a helium-neon ring laser (λ=0.63 μ). The parameters describing back reflections in the resonator were deduced from the modulation (at the difference frequency) of the intensities of the opposite waves in the laser. The changes in these parameters, which occurred when the tuning of the resonator was altered, were compared with the corresponding changes in the difference frequency. The experimental results were found to be in satisfactory agreement with the theoretical predictions of the influence of back reflections on the difference frequency in a ring laser.