Simulation and measurement of thermo-optical effects in an f-theta lens at high laser power

Multi-kilowatt lasers with high brilliance are gaining importance in laser material processing. But their use is accompanied by strong thermal loads on the optical elements for laser beam guiding and shaping. Absorption of laser energy in the bulk material and the coating causes local heating which induces an inhomogeneous refractive index profile and surface deformations. Commercially available optic design software such as Zemax OpticStudio cannot model such thermal effects. Thus, an interface between a Finite Element Analysis in Ansys and Ray-Tracing is used and has recently been extended to model surface deformations. It transforms the discrete temperature and deformation data into consciously functions which can be interpreted by OpticStudio. In this paper, the thermal effects of a multi-kilowatt f-theta lens are discussed and the simulation is compared to experimental focus shift measurements for the first time. Furthermore, strategies for compensating thermal effects are presented.