基于焦斑空间频率全域优化的偏振匀滑设计

偏振匀滑是利用光束偏振特性降低焦斑对比度的一种技术,它最大可降低焦斑对比度为原来的1/√2. 焦斑的频谱分析显示,传统楔形晶体的偏振匀滑对焦斑对比度的改善只集中在某些特定的空间频率,本文因此提出了一种可全域降低焦斑空间频率的偏振匀滑方法,它采用单轴晶体对入射光的角度不同而产生的相移不同的方法,实现激光两种正交偏振态在靶点的分离. 理论分析和数值模拟表明,新方法可以实现焦斑空间频率中高频段的全频域降低,焦斑对比度也可同时达到1/√2的最大程度的改善. 分析了连续相位板作为新方法引入激光入射角分布不同的条件,确定了刻蚀连续相位板面形的晶体同时实现焦斑整形和偏振匀滑的边界条件. 关键词： 偏振匀滑 焦斑功率谱 响应函数 焦斑整形

Polarization smo othing design for improving the whole spatial frequency at fo cal sp ot

Polarization smoothing is a technique for reducing speckle pattern contröst on a target by overlaying two uncorrelated speckle patterns with orthogonal polarizations, and it can reduce focal spot contröst by a factor of 1/√2. Improvement of focal spot contröst by using traditional polarization wedge for polarization smoothing is usually concentrated at some special spatial frequency and is lack of effect in physical experiments. To improve the spatial spectrum of polarization smoothing, a new method is proposed, in which two orthogonal polarization states are separated by the angle distribution differences of the beam direction angle and the uniaxial crystal optic axis; the angle can induce the optical phase differences between “o” and “e” light. Theoretical analysis and numerical simulation are carried out to analyze the new method. Results show that based on the viable control of beam random polarization state at near field, besides the reduction of the focal spot contröst by 1/√2, the new method can improve the whole spatial spectrum at the focal spot. The boundary conditions that continuous phase plate is used as the way to induce the been direction angle for polarization smoothing is obtained.
Keywords： polarization smoothing focal spot power spectrum response function focal spot shaping