High-power laser systems mostly use coherent or incoherent combined beams to achieve higher laser output power to satisfy the application. However, the far-field beam quality of laser will be reduced when propagating over atmosphere. Based on the propagation model of laser beams array, we use atmospheric coherence length, laser duration and average wind velocity to construct dynamic atmospheric turbulence which is characterized as a phase screen sequence. Meanwhile, considered as the indexes to evaluate beam quality, peak intensity and intensity in bucket are comparatively analysed in coherent and incoherent combined beams in far-field. The results indicate that in weaker turbulence circumstances, coherent combined beam has an advantage compared with the incoherent combined beams when laser duration is short, and coherent combination is more suitable for pulsed laser. With laser duration is increasing, the beam quality of incoherent and coherent combined beams both decrease and tend to be close. In stronger turbulence circumstances, the corresponding laser duration will be shorter when the beam quality of coherent combined beams is extraordinary close to that of incoherent combined beams. The researches can provide important data for high-power laser system to select the optimal beam combination mode to improve its performance.

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This paper uses an algorithm to shape from shading based on Finite-Element. According to Finite-Element principle, a smooth surface can be approximated by a group of triangular patches. The brightness of this triangular patch can be computed using reflectance map. This brightness can be regarded as the approximate brightness of the corresponding triangular area. With a linearized reflectance map, a square of brightness error function can be made. Then the result of minimizing the brightness error function is the corresponding surface height. The experiments on synthetic and real images show that the algorithm is very efficiency and accuracy.

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