Frequency-conversion modeling with spatially and temporally varying beams

摘要

Abstract: A computer model of third-harmonic conversion of Nd:glass laser radiation in KDP, including paraxial diffraction, walkoff, arbitrary temporal dependence, and B-integral effects, has been developed. The code is four-dimensional in that it includes the spatial field variations along and transverse to the propagation direction as well as temporal variations. A split-step algorithm based on the fast Fourier transform and a Runge-Kutta integrator is employed for forward stepping in space and time. The code has been benchmarked against results of simplified codes in the plane-wave or monochromatic limits, and predictions for conversion efficiencies are in good agreement with experimental results at Livermore. Spatial phase ripples and temporal bandwidth of the input wavefront are much more important in the tripling crystal(s) than in the doubler(s). Two-doubler designs allow for high tripling efficiencies over a broad range of intensities, while large bandwidths with high conversion efficiencies can be realized with two triplers. !9