Novel Adaptive Resonators and Thermal Lensing

摘要

We present different approaches to improve the beam quality of solid-state lasers. The original dual- or variable-configuration resonator was improved to emit completely polarised output. This was achieved by enforcing unidirectional operation due to the polarisation dependence of the thermal lenses and of the gain in Nd:YVO_4 crystals. Single-frequency operation was obtained in a miniaturised version of this resonator based on a polarising beam splitter made of Nd:YAG. Our transversally pumped high-power lasers feature output powers exceeding 600 W. In order to compensate for the power dependent thermal lenses we investigate the use of self-adaptive compensating thermo-optical elements which generate thermally induced lenses with the opposite sign as the lens in the gain medium. Furthermore, to speed up the optimisation processes we have derived a general analytical solution of the heat conduction equation for arbitrary heating distributions with cylindrical symmetry.