Patent ID: 7796671

Claim:
A method of configuring a multi-pass optical power amplifier to perform polarization-dependent amplification of laser energy to produce laser output with reduced beam distortion, comprising: providing an anisotropic gain medium comprising a rare-earth ion-doped crystalline solid state material having first and second orthogonally related gain axes characterized by inherent differential axial gain and associated inherent differential thermal birefringence; guiding a polarized seed laser beam for multiple passes through the anisotropic gain medium, the seed laser beam for each of the multiple passes propagating along a common beam path and undergoing substantially no displacement from the common beam path, and the seed laser beam having a polarization direction transverse to the common beam path; and coordinating alignment of the polarization direction of the polarized seed laser beam with the first and second gain axes of the gain medium to establish a number of the multiple passes through the gain medium by passing the polarized seed laser beam multiple times through a beam splitter and producing a laser output beam exiting the beam splitter; whereby the seed laser beam undergoing substantially no displacement from the beam path reduces laser output beam distortion and the inherent differential thermal birefringence enhances laser output energy extraction efficiency.