Effects of cascade nonlinear medium spatial configuration on optical field characteristics

The expression of the optical field distribution in arbitrary location after Gaussian beam passes through cascade nonlinear mediums is derived with Fourier transform method and Fresnel diffraction principle. The variation relation of the optical field peak intensity, the peak power location, beam width and modulation factor in the cascade nonlinear mediums is investigated. The result shows that the optical field peak intensity increases gradually, the peak-to-peak amplitude becomes shorter, the beam width becomes narrower, and the modulation factor becomes bigger as the nonlinear effects enhance. The configuration of the nonlinear mediums should be located equidistantly, and kept away from the peak location of the optical beam by all means. The equidistance of the nonlinear mediums has to be optimized to reduce the risk of the optical element damage.