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

TLDR

The study investigates wave‑front distortion from high‑power lasers on transmissive optics using a Shack–Hartmann sensor. The authors determine the coupling coefficient of a thermally aberrated Gaussian beam to the TEM00 cavity mode as a function of aberration magnitude, and compare the theoretical thermal phase profile with measurements on neutral‑density filter glass, Faraday glass, and lithium niobate. A single wave of thermally induced phase aberration reduces TEM00 coupling to 4.5 %, but optimal focus compensation raises it to 79 %, and the measured thermal aberration profiles agree with theory within the Shack–Hartmann sensor’s nanometer‑level sensitivity.

Abstract

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 1/e2 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.