Working beyond the static limits of laser stability by use of adaptive and polarization-conjugation optics

Strong thermo-optical aberrations in flash-lamp-pumped Nd:Cr:GSGG rods were corrected to yield TEM(00) output at twice the efficiency of Nd:YAG. A hemispherical resonator operating at the limit of stability was employed. As much as 3 W of average power in a Gaussian beam (M(2) approximately 1) was generated. Unique features were zero warm-up time and the ability to vary the repetition rate without varying energy, near- and far-field profiles, or polarization purity. Thermal focusing and astigmatism were corrected with a microprocessor-controlled adaptive-optics backmirror composed of discrete elements (variable-radius mirror). A reentrant resonator coupled polarizer losses back into the laser rod and corrected depolarization.