Axial mode locking in a cw YAG:Nd3+ ring laser

The first results are reported of forced phase mode locking in a cw YAG:Nd³⁺ ring laser. The locking was produced by inserting an electrooptic LiNbO₃ phase modulator in the resonator. The modulator varied the resonator perimeter at the intermode beat frequency. The time, spectral, and frequency characteristics of the laser were investigated in the phase mode locking regime. The width of the locking band was determined. In the phase locking regime the competition between the opposite waves was much weaker and there was also a reduction in the locking range when the ring laser was rotated. Moreover, spontaneous axial mode locking was observed in the absence of periodic variations of the resonator parameters.