Phase dynamics in the self-modulation oscillation regime in a solid-state ring laser

The dynamics of the phase difference of counterpropagating waves is studied theoretically and experimentally in the self-modulation oscillation regime in a solid-state ring laser. It is found that in the case of a small enough frequency nonreciprocity of the ring resonator, the phase difference of counterpropagating waves changes within a limited range, performing periodic oscillations with the intensity self-modulation frequency. The instant frequency difference of counterpropagating waves also changes periodically in time; however, its mean value is zero (the frequency locking for counterpropagating waves takes place). The width of the frequency locking region is measured. It is shown that the phase difference of the coupling coefficients considerably affects the phase dynamics. This opens up new possibilities for determining the phase difference of coupling coefficients of counterpropagating waves.