Ghost analysis visualization techniques for complex systems: examples from the NIF final optics assembly

Abstract

The stray light or �ghost� analysis of the National Ignition Facility�s (NIP) Final Optics Assembly (FOA) has proved to be one of the most complex ghost analyses ever attempted. The NIF FOA consists of a bundle of four beam lines that: 1) provides the vacuum seal to the target chamber, 2) converts l(omega) to 3(omega) light, 3) focuses the light on the target, 4) separates a fraction of the 3(omega) beam for energy diagnostics, 5) separates the three wavelengths to diffract unwanted 1(omega) & 2(omega) light away from the target, 6) provides spatial beam smoothing, and 7) provides a debris barrier between the target chamber and the switchyard mirrors. The three wavelengths of light and seven optical elements with three diffractive optic surfaces generate three million ghosts through 4 th order. Approximately 24,000 of these ghosts have peak fluence exceeding 1 J/cm 2 . The shear number of ghost paths requires a visualization method that allows overlapping ghosts on optics and mechanical components to be summed and then mapped to the optical and mechanical component surfaces in 3D space. This paper addresses the following aspects of the NIF Final Optics Ghost analysis: 1) materials issues for stray light mitigation, 2) limitations of current software tools (especially in modeling diffractive optics), 3) computer resource limitations affecting automated coherent raytracing, 4) folding the stray light analysis into the opto-mechanical design process, 5) analysis and visualization tools from simple hand calculations to specialized stray light analysis computer codes, and 6) attempts at visualizing these ghosts using a CAD model and another using a high end data visualization software approach.