基于阶梯相位调制的窄谱激光主动照明均匀性

Active illumination uniformity with narrow spectrum laser based on ladderlike phase modulation

提出一种基于阶梯相位调制的窄谱激光主动照明方法,利用阶梯型相位调制器对窄谱激光进行相位调制,提高照明激光到达目标处的光斑均匀性和稳定性.建立了窄谱激光阶梯相位调制和照明激光远场光斑均匀性的理论模型,搭建了光束经过1.8 km水平传输的窄谱激光主动照明实验平台,通过5阶梯相位调制器对0.05 nm线宽的照明激光进行相位调制,实现了照明激光远场光斑匀化实验.实验结果表明,通过5阶梯相位调制器进行相位调制后,远场光斑包含57%能量区域的空间闪烁率从0.73改善到0.33,中心光强时间闪烁指数从0.38改善到0.14,照明激光远场光斑均匀性和稳定性都得到明显提升.

Active illumination is a crucial technology for active imaging,active tracking and aiming system.But the atmosphere turbulence distributed over the entire path causes the intensity to fluctuate,which reduces the illumination uniformity seriously.Therefore,it is desirable to find ways to reduce the intensity fluctuation and improve the uniformity of active illumination.It has been revealed that one can improve illumination uniformity by using multi-beam laser illuminator.Another effective approach is partially coherent beam illumination.In this paper,a novel method is suggested to improve the illumination uniformity.Phase disturbance is induced by a ladder-like phase modulator(LPM)and the transmitting field of narrow spectrum laser is confused,and thus the atmosphere turbulence will be compensated and the illumination uniformity will be improved.The physical models of narrow spectrum laser phase modulation and atmosphere propagation are deduced,and the expression of the facular distribution is obtained.The active-illumination experimental setup with a laser propagation distance of 1.8 km through horizontal atmosphere is established.Based on the facular distribution of illumination laser at 1.8 km,the uniformity and stabilization are achieved.The experimental results indicate that the illumination uniformity and stabilization are both improved.The spatial and central time scintillation indexes are improved from 0.73 to 0.33 and from 0.38 to 0.14,respectively.