Numerical and experimental study of thermally induced wavefront aberration in a direct-liquid-cooled Nd:YLF thin-disk laser gain module

The wavefront aberration induced by thermally in a direct-liquid-cooled Nd:YLF thin-disk laser gain module is investigated numerically with the laminar flow pattern. We find that the liquid layer plays the major role in causing of the wavefront aberration in the gain module. The wavefront aberration is quantitatively evaluated by optical path difference (OPD) and can be fitted by Legendre polynomials. Besides the main aberrations of tilt and defocus, the higher order aberrations can also be well described by the Legendre polynomial of some certain orders. The OPD distributions are compared by varying the pumping and flowing states. In the experiment, a direct-liquid-cooled Nd:YLF thin-disk laser gain module is developed and the experimental measurements are performed to validate the reliability and precision of numerical results with the flow velocity of 4 m/s, channel thickness of 0.5 mm, pump uniformity of 92% and pump power of 5 kW. Both the calculated and measured results can provide a reference for structure design and wavefront aberration analysis of the direct-liquid-cooled Nd:YLF thin-disk laser.