Mitigation of BSG damage caused by upstream flaw in the final optics assembly

Abstract

In high-power laser facilities for the inertial confinement fusion, there are many large-radius optical elements, which inevitably have some flaws on the surface. The flaws can cause optical intensity intensification and therefore damage the optical elements in the downstream, especially for the beam sampling grating (BSG), which is an important element in the final optics assembly. In this paper, several physical models are established to study the optical field enhancement in the BSG position modulated by upstream flaw. Firstly, when only the linear transportation is considered, it is found that there is a peak or valley of the maximum intensity after the focus lens compared with the ideal wave front. Meanwhile the influence of flaw has an effective range. Secondly, when the nonlinear effect of the focus lens is also considered, the peak maximum downstream is much bigger than the one for the linear consideration and the damage risk of the BSG there is much higher too. From the simulation, we can see that it is important to place the BSG in a properly selected position to mitigate the laser induced damage. The results could give some references to the mitigation of BSG damage caused by upstream flaws and the layout of the final optics assembly.