Theory of a single-frequency solid-state ring laser

An investigation is made of the mechanism of spontaneous antiphase fluctuations of the intensity of the opposite waves in a solid-state ring laser. It is found that backscattering-induced coupling of the waves is only responsible for fluctuations at a frequency higher than that of the relaxation oscillations. A hypothesis is put forward that the lower-frequency fluctuations may be due to instability of the laser parameters. Computer calculations using a laser model with low-frequency antiphase modulation of the opposite wave losses confirm that this interpretation is feasible.