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焦斑的尺寸和形状主要由光束的波前畸变决定。为了减小大口径激光系统的波前畸变并提高焦斑能量集中度,对静态波前畸变采用了相位板补偿的方法。对于在建中的原型装置,主要考虑补偿主放大系统的波前畸变。根据补偿板摆放位置处的光通量和加工的难易程度,综合考察了四个摆放位置的优缺点,提出用补偿板替代腔镜对波前进行补偿。建立了求解补偿板面形的数值计算模型,就设计时采用的钕玻璃片滤波截止频率做了讨论,得出用0.01 mm-1的截止频率做低通滤波后可以得到最佳补偿效果,给出了补偿板的面形分布和加工方法。模拟结果表明,采用这种方法后静态波前畸变由3.35λ降到1.27λ;包含总能量95%的衍射极限倍数由6.21TDL降到了3.95TDL,说明焦斑能量集中度得到显著提高。
The size and shape of the focal spot is mainly determined by the wavefront distortion of the beam. In order to reduce the wavefront distortion and increase the focal spot energy concentration of the large-aperture laser system, a method of phase plate compensation is adopted for the static wavefront distortion. For the prototype under construction, the main consideration is to compensate the wavefront distortion of the main amplification system. According to the luminous flux at the position of the compensation plate and the ease of processing, the advantages and disadvantages of the four positions are comprehensively investigated. It is proposed that the compensation plate be used to replace the cavity mirror to compensate the wavefront. The numerical model for solving the compensation plate surface shape is established. The filter cutoff frequency of neodymium glass plate used in the design is discussed. It is concluded that the optimal compensation effect can be obtained by using the cutoff frequency of 0.01 mm-1 Out of the compensation plate surface shape distribution and processing methods. The simulation results show that the static wave front aberration decreases from 3.35λ to 1.27λ using this method, and the diffraction multiple of 95% of the total energy decreases from 6.21TDL to 3.95TDL, which shows that the focal spot energy concentration is significantly improved.