Wittman M D, Craxton R S
Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299, USA.
Appl Opt. 1999 Sep 1;38(25):5365-71. doi: 10.1364/ao.38.005365.
The sphericity and wall-thickness uniformity requirements of direct-drive inertial-fusion targets are of the order of less than 1%. These shells display self-interference patterns (SIP's) when irradiated with a spatially incoherent, narrow-bandwidth light source and viewed with a compound microscope. These patterns are distinct concentric fringes when the target is uniform, whereas faint, distorted, or discontinuous fringes indicate a nonuniform target. We determined the wall thickness to within +/-0.5 microm by counting the number of fringes in the SIP, independent of the outside diameter. Thickness uniformity is verified to an accuracy better than 0.05 microm. The wall thickness of gas-filled targets can be determined to this accuracy without knowledge of the type of gas or its pressure. The SIP fringe technique is used to select polymer shells typically of 800- to 1000-microm diameter and 5- to 12-microm wall thickness. The fringe locations have been modeled by use of ray tracing and agree well with actual measurements of well-characterized shells. Details of the formation of the SIP fringes, a theoretical model, and the method used for quantitative measurement of the shell-wall thickness with the SIP are presented with validation examples.
直接驱动惯性聚变靶丸的球度和壁厚均匀性要求在1%以内。当用空间非相干窄带光源照射并用复式显微镜观察时，这些靶丸会呈现自干涉图样（SIP）。当靶丸均匀时，这些图样是明显的同心条纹，而微弱、扭曲或不连续的条纹则表明靶丸不均匀。我们通过计算SIP中的条纹数量确定壁厚在±0.5微米以内，与外径无关。验证了厚度均匀性的精度优于0.05微米。在不知道气体类型及其压力的情况下，充气靶丸的壁厚也能确定到这个精度。SIP条纹技术用于挑选典型直径为800至1000微米、壁厚为5至12微米的聚合物靶丸。通过光线追迹对条纹位置进行了建模，与特征明确的靶丸的实际测量结果吻合良好。给出了SIP条纹形成的细节、理论模型以及利用SIP定量测量壳壁厚度的方法，并附有验证示例。
