Evaluating the effect of transmissive optic thermal lensing on laser beam quality with a Shack-Hartmann wave-front sensor

We examine wave-front distortion caused by high-power lasers on transmissive optics using a Shack-Hartmann wave-front sensor. The coupling coefficient for a thermally aberrated Gaussian beam to the TEM00 mode of a cavity was determined as a function of magnitude of the thermally induced aberration. One wave of thermally induced phase aberration between the Gaussian intensity peak and the 1e2 radius of the intensity profile reduces the power-coupling coefficient to the TEM00 mode of the cavity to 4.5% with no compensation. With optimal focus compensation the power coupling is increased to 79%. The theoretical shape of the thermally induced optical phase aberration is compared with measurements made in a neutral-density filter glass, Faraday glass, and lithium niobate. The agreement between the theoretical and the measured thermal aberration profiles is within the rms wave-front measurement sensitivity of the Shack-Hartmann wave-front sensor, which is a few nanometers.