Use of a feedback loop for the stabilization of a beat regime in a solid-state ring laser

Theoretical and experimental investigations were made of the influence of a magnetooptic feedback loop creating a difference between the losses for opposite waves, proportional to the difference between their intensities, on the amplitude and frequency characteristics of a rotating solidstate ring laser with a homogeneously broadened luminescence line of the active substance. Analytic solutions were obtained for the description of possible lasing regimes and a study was made of their stability for arbitrary values of the difference between the frequencies of the opposite waves. It was found that a feedback loop with a large transfer coefficient was capable of ensuring stable and simultaneous lasing under several regimes. It was established experimentally that optimization of the parameters of the loop in a rotating YAG:Nd³⁺ ring laser resulted in stabilization of the beat regime and expanded significantly the range of existence of this regime. The inertia of the feedback loop observed on increase of its transfer coefficient resulted in an instability of bidirectional lasing, giving rise to antiphase oscillations of the intensities of the opposite waves. A study was made of the transient processes which occurred as a result of abrupt changes in the signal in the feedback loop. The results of theoretical investigations were in good agreement with the experiments.