摘要
提高系统能量转换效率与输出光束质量一直是研制高功率固体激光系统极为关注的两类重要问题。多程放大系统因能够较大提高系统的输出能力，故得到较为广泛的应用；但由于多程放大级各类波前误差的相干叠加，使系统输出激光的波前发生比较严重的畸变，导致光束质量的下降。在高功率固体激光系统总体设计中，为了使光束质量满足高效率三倍频和小孔进腔打靶的要求，必须对激光的波前畸变进行校正。波前校正技术应用需根据系统波前误差的分布特性来设计，因此如何合理使用波前校正技术是总体设计必须解决的主要问题之一。本文主要就这一问题进行了以下几方面的系统研究：
1．比较全面地分析了系统内部波前误差与光束焦斑尺寸之间的关系，找到了波前梯度分布与焦斑能量分布之间的本质联系，提出了一个与焦斑尺寸关系最密切的波前误差参数，并采用数值模拟和统计的方法得到了焦斑尺寸限制条件所要求的波前误差限制条件；
2．进一步研究了多程放大系统中光学元件波前误差的叠加规律，并考虑到钕玻璃片加工工艺的相似性所导致的波前相关性，将相关系数耦合到波前误差叠加公式中，使修正后的公式能更准确地预估系统静态波前和分配光学元件加工精度要求；
3．完成了多程放大系统中波前误差的实验测量，初步掌握了类似构型高功率固体激光系统的波前误差分布特性，从而进一步明确了对波前校正系统校正能力的要求，为新一代高功率固体激光装置波前校正系统的优化设计提供了依据；
4．分析了变形镜的结构特点，初步给出了变形镜本身驱动单元数与校正量之间的制约关系；引入“二次补偿”波前校正方案，解决了变形镜校正量有限与高功率固体激光系统波前误差起伏量大的矛盾，建立了波前校正对象优化分配、静态校正器优化设计等细节过程所需要的方法，通过仿真模拟验证了“二次补偿”波前校正方案对于降低变形镜校正量要求和放宽光学元件加工精度的作用；
5．另外，作为一部分相对独立的内容，本文对宽频带激光传输条件下采用角锥棱镜阵列抑制低频波前畸变的设想进行了探索性的研究，通过仿真模拟验证了角锥棱镜阵列具有抑制低频波前畸变、提高激光焦斑能量集中度的显著作用，并初步验证了宽频带激光传输条件下近场振幅高频调制的匀滑效应。
How to improve the output energy and beam quality were two most noteworthy problems in the building of high power solid-state laser facility. The multi-pass amplifier was being adopted proverbially, which could improve the output energy consumedly. But on the other hand the beam quality was degraded by the severe wave-front's aberration that exacerbated by multi-passing the beam through the amplifier. To ensure the beam quality reach the requirement of high efficiency third harmonic conversion and small focal spot size, the correction of wave-front aberration had to be considered in the design of high power solid-state laser facility. The wave-front correct system should be designed according to the wave-front aberration's characters of optic system. So how to use the wave-front correct technology reasonably became one of the most important problems. Concerned this problem, the following questions were investigated in this paper:
1. The relationship between wave-front aberration and focal spot size was researched roundly, and the essential connection between focal spot energy shape and wave front gradient distribution was discovered, and a smarter parameter to evaluate wave front aberration was founded. Based on this, the wave front aberration tolerance confined by focal spot size requirement was obtained through calculation and statistics method.
2. The wave-front aberration's cumulating of optics elements in multi-pass amplifying system was researched more deeply. Considering the correlation between optics elements' wave-front aberrations caused by the similar fabrication technique, the correlation coefficient was adopted to revise calculation rule of superimposition which used in estimating system's static wave-front aberration and allocating optical machining precision.
3. The measuring of multi-pass amplifying facility's wave-front aberration was achieved, and the character of wave-front aberration in such high power solid-state laser facility was mastered primarily, then the requirement for wave correct system was found out more clearly which would provide support for high power solid-state facility's optimum design.
4. The structure and character of deformable mirror were analyzed, and the conflict between the deformation band and the pitch of deformable cells was pointed
out. The "two-time compensation" wave-front correct mode was introduced to settle that conflict. The method for allocating wave-front aberration and designing static corrector was found, and the "two-time compensation" wave-front correct mode was validated by simulation.
5. Otherwise, the applicability of cube comer array in the wide spectrum high power solid-state laser facility was researched as a relatively absolute part in this paper. Through simulation, the action of cube corner array to reduce beam's focal spot size was testified visibly, and the smoothing effect of beam's modulation caused by cube corner array was proved primarily on the wide spectrum condition.
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