Aberration correction in double-pass amplifiers through the use of phase conjugate mirrors and/ or adaptive optics

摘要

Corrrection of birefringence induced effects (depolarization and bipolar focusing) was achieved in double-pass amplifiers using a Faraday rotalor placed between the laser rod and the retroreflecting optic. A necessary condition was that each ray in the beam retraced its path through the amplifying medium. Retrace was limited by imperfect conjugate-beam fidelity and by nonreciprocal double-pass indices of refraction. We compare various retroreflectors: stimulated Brillouin scatter phase-conjugate-mirrors (PCMs), PCMs with relay lenses to image the rod principal plane onto the PCM entrance aperture (IPCMs), IPCMs with external, adaptively-adjusted. astigmatism-correcting cylindrical doublets, and all adaptive optics imaging variable-radius-mirrors (IVRMs). Results with flashlamp pumped, Nd:Cr:GSGG double-pass amplifiers show that average output power increased fivefold with a Faraday rotator plus complete nonlinear optics retroreflcctor package (IPCM+cylindrical zoom), and that this represents an 80 percent increase over the power achieved using just a PCM. Far better results are, however, achieved with an IVRM.