A Nd:YAG laser with a vectorial phase conjugate mirror in the gain medium

Summary form only given. It has been known for long that thermal dissipation in the rod of a solid state laser induces a distortion of the output beam, due to birefringence and thermal lensing (bifocusing). Birefringence can be compensated by polarization rotation in the cavity, but thermal lensing can be only corrected to first order, and at a fixed input power. It has been established that vectorial phase conjugation provides both birefringence and thermal lensing compensation to any order. We show that a standard, flash-lamp pumped pulsed Nd:YAG laser can be turned into an efficient phase conjugate resonator by vectorial four wave mixing in the gain medium.