猫眼效应中离焦量对激光回波发散角的影响

平行光束或者激光束在光轴方向上照射焦平面成像系统时会产生猫眼效应，焦平面探测器安装的正交性与离焦量直接影响猫眼回波的光学特性，进而影响基于猫眼效应的探测系统的性能。针对猫眼效应中离焦量与后向反射光束发散角之间关系，利用物理光学进行分析，建立理论模型，对焦距为0.18 m的焦平面探测成像系统进行数值计算得到:在离焦量为0.16 mm时，发散角最小（0.019 mrad）。搭建实验系统，测试离焦量与猫眼回波发散角，测得离焦量在0.15 mm附近存在最小的发散角为0.025 mrad，与计算结果0.019 mrad基本吻合。研究表明:1） 负离焦对发散角的影响大于正离焦；2） 猫眼回波发散角基本上随着离焦量绝对值的增加而变大，但是变化曲线并不关于零离焦量点对称，而是在某个正离焦处存在一个最小发散角。

Impact of defocus on divergence of reflected light beam in cat-eye effect

Cat-eye effect occurs when a parallel beam or a laser beam illuminates a focal plane imaging system in the direction of optical axis, where the orthogonality and defocus of the detector in relation with the optical axis and focal plane affects directly the property of the reflected light beam, further affects the performance of cat-eye effect based detecting system. The relation between the defocus amount and the divergence of reflected beam was investigated through both theoretical analysis and numerical calculation.When the defocus is 0.16mm, the minimum divergence angle is 0.019 mrad. Furthermore, an experimental system was set up to test the defocus and divergence, When the defocus is 0.15 mm, the minimum divergence angle is 0.25 mrad,indicating the test result agrees well with the calculation. The conclusions drawn from the investigation are as follows:1） the impact of negative defocus on the divergence of reflected beam is greater than that of positive defocus； 2）the divergence angle of the cat-eye reflected beam increases virtually along with the increasing of absolute defocus, but the function diagram of the divergence is not symmetric in shape with respect to the zero defocus point, rather, a unique minimal divergence exists at a certain positive defocus point.