Stray light analysis has been carried out for the main laser section of the National Ignition Facility main laser section using a comprehensive non-sequential ray trace model supplemented with additional ray trace and diffraction propagation modeling. This paper describes the analysis and control methodology, gives examples of ghost paths and required tilted lenses, baffles, absorbers, and beam dumps, and discusses analysis of stray light 'pencil beams' in the system.
The stray light or 'ghost' analysis of the NIF 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 1 (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) and 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 even optical elements with three diffractive optic surfaces generate three million ghosts through 4th order. Approximately 24,000 of these ghosts have peak fluence exceeding 1 J/cm<SUP>2</SUP>. The shear number of ghost paths requires a visualization method that allows overlapping ghosts on optics and mechanical components to be summoned 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, 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.
Ghost reflections are a major consideration in the optical design of the National Ignition Facility. The first-order layout (e.g., spacing between components), the lens shape, and the dimensions of the building are strongly affected. In this paper we will describe the principal ghost reflections that drive the system configuration. Several specific examples will be shown to illustrate how dangerous ghost reflections are avoided and stray light concerns are managed.
End-to-end modeling of the photometric performance of LCD projection system using Monte Carlo geometrical ray tracing methods is an accurate and precise tool for predicting and improving the performance of these deices before, during and after product development. However, an accurate simulation first requires considering which physical properties contribute most to the system's photometric performance. Second, these properties must be characterized by physical measurements and translated into the tangible modeling parameters of a ray tracing program. Third, the implications of using a Monte Carlo ray tracing algorithm, and in general any other optical transformation algorithm, on radiometric accuracy must be well understood. These considerations as well as a generalized approach to the characterization and simulation of an LCD projector are described. A commercially available ray tracing program, the Advanced Systems Analysis Program, is used to demonstrate this approach. The irradiance uniformity, CIE color performance and screen brightness of an arc source LCD projector system are computed as an example.