高能拍瓦激光系统中大口径离轴抛物面聚焦特性研究

为进行快点火实验,需对高能拍瓦激光聚焦系统中的核心元件即大口径离轴抛物面,进行深入量化研究,以便对其结构选型和精密调整提供准确的理论依据。利用基于严格的矢量衍射理论的数值计算方法,并结合像差分析得到了大孔径、大离轴量的抛物面镜(OAP)的物理光学成像特性。首先用理想平行光入射,得出OAP的三维平动公差与其焦深密切相关,OAP绕旋转对称轴的转动可归结为平动问题,其公差与焦深也有简单关系;入射光轴失准时,像散占主导作用,并可由一结构因子来定性描述其对像斑的影响。其次当入射光有一定的发散角时,除引起最佳像面位置变化外,还会由于OAP不对称性而引起的彗差使得像斑的峰值光强大大降低,并论述了OAP的结构参数对此的影响。

Study on Focusing Characteristic of Large Aperture Off-Axis Paraboloidal Mirror in the High-Energy Petawatt Laser System

To realize the fast ignition experiments, deep and quantitative research needs to be taken on the large aperture off-axis paraboloidal mirror (OAP) which is the core component in the high-energy petawatt laser focusing system, in order to provide an accurate basic theory for the OAP structure model selection and precision adjustments. This paper uses a numerical calculation method based on the rigorous vector diffraction theory combining with wavefront aberration analysis, by which the physical optical imaging characteristics of a large aperture and far off-axis OAP are obtained. First, using parallel light incidence, a conclusion can be obtained that the tolerances of OAP translation and revolving around its symmetric axis are closely related with its focal depth. When the optical axis misalignment occurs, astigmatism will play a leading role in the influence on the optical spot which can be described qualitatively by a structural factor. Then, when the incident light has a divergence angle, the best image plane location will change and coma is produced to decrease the power density of the optical spot owing to the asymmetry of OAP. The discussion of the influence affected synchronously by the structural parameters of OAP is also presented.