Design considerations for high-power TEM oo operation of end-pumped solid state lasers

A resonator design strategy for high-power end-pumped solid- state lasers is described, which reduces the beam distortion due to thermally-induced lens aberrations. The approach is based on a resonator design satisfying two criteria: firstly, the laser mode radius must be appreciably smaller than the pump beam radius, and secondly, the laser mode size must decrease with decreasing power (increasing focal length) of the thermal lens. Experimental results are presented for diode-bar-pumped Nd:YAG lasers confirming the validity of this approach. A simple technique, employing a single quarter-wave plate, for reducing the depolarization loss due to thermally-induced birefringence is also described. Using this approach, the depolarization loss for a diode-bar-pumped Nd:YAG laser operating at 946 nm has been reduced from approximately 1.7% to <0.001%, resulting in 2.9 W of linearly-polarized output for 14.3 W of incident pump power.