Optical pumping of solid-state lasers induces thermal lensing in the laser crystal. This lansing determines the beam properties in the resonator; the TEM00-mode radiation is limited to a small laser rod volume and it depends on the pump power. Especially with pulse-pumped systems, the generation of stable fundamental mode radiation could only be obtained with low efficiency. Laser resonators with optimum TEM00mode output were studied considering the thermal lensing. A kind of resonator was found, the radiation of which is insensitive to thermal distortions. The following is determined by parameters : , where and are distances between rod ends and mirrors, and being the distances between the two mirrors and the lens. The predicted beam behavior was verified experimentally with a high repetition rate YAG laser. A high-precision laser drilling machine was constructed with this design. Because of the insensitive properties, reproducible material processing was achieved in industrial use.