Simulation And Analysis Of Nonlinear Effect In High Power Laser System Based On Ray-tracing

In high power laser systems, third-order nonlinear effect is the key factor in leading to beam wavefront aberration, beam quality degradation, and even leading to nonlinear self-focusing and "Hot Spot" effects. How to reduce the impact of nonlinear effect, how to improve the beam quality, and how to improve the performance of high power laser systems, have always been concerned by the designers.Based on geometrical optics method, real ray-tracing is applied to the simulation and analysis of nonlinear effect in high power laser systems. Our research works focus on the impact of third-order nonlinear effect of Kerr medium on beam propagation and beam quality. Based on the accomplished nonlinear ray-tracing program, hybrid modeling for linear and nonlinear media is realized through programming in this paper. A focus system with KDP crystal as the nonlinear media is taken as an example, and simulation analysis of the influence of nonlinear effect on beam quality is conducted with different laser power density. Based on the simulation results, an optimization method, which is taking the optical element intervals as compensation without changing the position of the focal plane, is presented. Besides, real surface modeling is realized through measuring the lens surface figure errors. The simulation of nonlinear beam propagation is conducted, and a compensation method of element rotation is feasible to reduce the modulation of surface figure errors on beam. Considering the complicated light path of high power laser systems and the poor interactivity of traditional modeling method, a new modeling method which is based on elements and components is presented. This paper mainly deals with the work of components design and function realization.Since ray-tracing method applied in this paper without paraxial approximation, it is able to consider both the system aberrations and lens surface figure errors in the simulation of nonlinear propagation, and the simulation results and compensation methods can provide some guidance to the design, fabrication and alignment of high power laser systems. Besides, the realization of a new modeling method for high power laser systems and the establishment of components libraries provide great convenience for high power laser systems design work.One paper on nonlinear degeneration and compensation of beam quality in high power laser system has already published on <Acta Optica Sinica>.