New diode pumped multi KW solid state laser - modeling of the performance in comparison with experimental results

High power diode pumped solid stale lasers are attractive sources for various applications in material processing. One of the advantages of diode pumping of solid state lasers is the higher brilliance (maximum output power/poorest beam parameter product using equal plan-plane resonators) compared to are lamp pumped solid state lasers. The solid state laser we report on is a side pumped Nd:YAG rod laser. Ten pump modules each consisting of 13 diode lasers, are arranged in a ten fold symmetry. The pump radiation is concentrated into the diffuse reflecting cavity by non imaging optics. For designing the non imaging optics a ray tracing model was developed to calculate the distribution of absorbed pump power. In order to get a nearly aberration free thermal lensing it is important to get smooth formed pump power. To examine the aberrations influence on output power and beam quality we have set up a model that includes all physical aspects relevant in the high power region. Temperature and stress inside the rod are computed with the help of finite element program using the ray tracing results. Temperature and stress distribution in the Nd:YAG rod are used to describe the thermal lensing and birefringence of the rod with a two dimensional complex field of Jones matrices. The Jones matrices are used by an optical simulation program to compute beam propagation within and outside the optical resonator. Both directions of polarization and their coupling are considered. A large number of different laser arrangements have been simulated with this model. We have varied the coupling of the diode radiation as well as some of the laser parameters. The results are in good agreement with the experimental results. A CW output power of 1.1 kW with a beam parameter product better than 20 mm x mrad over the full power range of a single rod laser has been demonstrated.