Surface error modeling, evaluation and optimization of large optics in inertial confinement fusion laser system

Highlights: • A surface error numerical modeling methodology is proposed to evaluate both offline and online mirror surfaces. • A close-loop assembly process can optimize the mounting induced error within 200 nm. • Gravity's positive effect on the surface error provides more reasonable selective assembly strategy for large laser transport mirrors. - Abstract: Surface errors of mounted large optics have significant impacts on laser performance in high power laser system. However, in SG-III inertial confinement fusion (ICF) laser system, it is really tough to realize the minimized surface error and satisfy the design criterions. In this paper, the compositions and corresponding causes of complicated surface topographies are analyzed systematically. Surface decoupling, reconstruction and fitting methods are proposed successively and constitute an integrated surface modeling methodology to visualize and evaluate both offline and online mirror surfaces. Further, we present a closed-loop "mounting – inspection – optimization" assembly process based on the combination of interferometric measuring, finite element simulation and digital reconstruction, which will lead the mounting induced surface error of the large optics to meet the wavefront criterions. Through a case study of the large aperture laser transport mirror, the proposed approach is proved to have good performance on both improving optical mounting performance and obtaining accurate surface features.