Thermal lensing measurement from the coefficient of defocus aberration using Shack-Hartmann wavefront sensor

In this paper we experimentally demonstrate the measurement of thermally induced lensing, using a Shack-Hartmann wavefront sensor. We measured the thermally induced lens from the coefficient of defocus aberration using a Shack-Hartmann wavefront sensor (SHWFS). As a calibration technique, we infer the focal length of standard lenses probed by a collimated Gaussian beam of wavelength 633 nm. The technique was applied to an Nd:YAG crystal that is actively pumped by a diode laser operating at 808 nm. The results were compared to the results obtained by changing the properties of the end-pumped solid-state laser resonator operating at 1064 nm, where the length of an unstable plane-parallel laser resonator cavity is varied, and the laser output power was measured.