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Improvement of the output power of low divergence, high power lasers using a passive phase correction made of simple lenses

This paper proposes an alternative method to correct the thermal effects, using two of their properties: first, as the characteristic time of thermal effects is in the order of a few seconds, they are stable over time in cw or high-repetition rate lasers, which enables a passive correction. Second, the optical distortion due to the thermal effects is spherical aberration. By choosing judiciously a combination of lenses, it is possible to build an optical system whose spherical aberration is the opposite of the one of transversally-pumped cylindrical laser rods.