An efficiency computing method is presented to obtain the magnifying-ratio of beam expander. The illuminating area of laser beam can be computed according to the refraction index and beam spread function (BSF) which has already considered forward-scattering process. The magnifying-ratio range of beam expander should be 0.925~3.09 in order to obtain about φ1m illuminating area when the distance between laser and target is 10~40m. A magnifying-ratio variable beam expander is designed according to computation. Underwater experiments show that this beam expander plays an effective role on illuminating in underwater high-repetition-rate range-rated Imaging system.
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Wei Zhong, Xiaohui Zhang, "Design of laser beam expander in underwater high-repetition-rate range-gated imaging system," Proc. SPIE 9676, AOPC 2015: Optical Design and Manufacturing Technologies, 96760K (15 October 2015);