Method and apparatus for compensating for wave front distortion in a slab laser

A method of operating a slab laser, said slab laser comprising a solid-state lasing medium having a longitudinally extending lasing axis, pumping means adjacent said lasing medium for impinging electromagnetic radiation upon said lasing medium, and cooling means for flowing a fluid coolant across at least a portion of said lasing medium, said lasing medium exhibiting a negative focal power lens effect in lateral edge portions thereof, said method comprising the steps of:

• (a) introducing a positive focal power lens effect approximately equal in magnitude to said negative focal power lens effect to a central portion of said lasing medium between said lasing medium lateral edge portions, said positive focal power effect being introduced by creating a thermal lens effect in said central portion;
• and
• (b) passing a beam of coherent light having a wavefront including multiple rays at least twice through said lasing medium in a direction generally along said lasing axis such that said rays in said wavefront traverse alternate regions of positive and negative focal powers of approximately equal magnitudes.