The Effect of Intracavity Subharmonic Phase Modulation on a Nd:YAG Laser.

摘要

A Nd:YAG laser propagating in the TEM sub 00 mode was phase modulated by an intracavity lithium niobate crystal that was driven at a subharmonic frequency equal to one half the frequency difference between the free-running modes. Experimental results showed that the subharmonic frequency caused low amplitude subharmonic modes to be injected by single-pass modulation into the scanning Fabry-Perot interferometer display of the free-running modes, which otherwise remained unperturbed. When a spectrally impure RF drive, primarily composed of the sub-harmonic and twice this frequency, was allowed to phase modulate the laser, mode-locking resulted because of the residual harmonic power in the signal. As phase-state switching randomly occurred, subharmonic modes either appeared or disappeared in the interferometer display of the phase-locked modes. This effect was theoretically shown to be a result of the phase relationship between the subharmonic frequency of the RF drive and the electric field in the cavity, a relationship that changed by pi/2 radians whenever phase-state switching occurred.