15 October 2015 Design of laser beam expander in underwater high-repetition-rate range-gated imaging system
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Proceedings Volume 9676, AOPC 2015: Optical Design and Manufacturing Technologies; 96760K (2015) https://doi.org/10.1117/12.2199219
Event: Applied Optics and Photonics China (AOPC2015), 2015, Beijing, China
Active underwater imaging systems, using an artificial light source for underwater target illumination, have preferable practical value in military and civil domain. Back-scattering of water impacts imaging system performance by reducing image contrast, and this is especially bad when the light source is close to the camera. Range-gated technique can effectively rejecting the back-scattering of water and improve the range of underwater target detection, while it can only collect image at certain distance for every laser impulse. High-repetition-rate green laser is a better light source in underwater range-gated imaging system. It has smaller pulse energy, while it can improve the imaging result. In order to illuminate the proper area underwater according to the different distance between the laser source and targets, there must be a magnifying-ratio variable beam expander to adjust the divergent angle of the laser. Challenges associated with magnifying-ratio computation and designing of beam expander are difficult to overcome due to the obvious refraction and forward-scattering of water.

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.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Wei Zhong, Wei Zhong, Xiaohui Zhang, 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); doi: 10.1117/12.2199219; https://doi.org/10.1117/12.2199219

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