The focal length of the spatial filter and final focus lenses for the National Ignition Facility are measured to < + 0.01% using a combination of master lenses and production-oriented techniques for relative focal length.
The incorporation of an optical timing fiducial onto a time-resolved x-ray streak record permits one to precisely relate the x-ray emission to the incident laser pulse. At the Laboratory for Laser Energetics, our approach to recording fiducials is twofold. In addition to recording the x-ray emission on a bifurcated photocathode, we also streak the incident laser light at 351 nm, which is scattered from the target and an independent signal at 4ω0 (264 nm), which is derived by frequency quadrupling a tiny fraction of the OMEGA laser driver output. The signal at 4ω0 is transported through the vacuum wall to the streak camera photocathode via fiber optics. A 200-Å aluminum layer on mica is utilized for the UV sensitive photocathode. We will present examples and further details of this system.
Tinsley, under JWST funding, has led the team that has developed a novel and highly versatile piece of ground support equipment for optical surface testing of JWST beryllium mirror segments during optical fabrication. The infrared Scanning Shack Hartmann System (SSHS) offers the advantage of being able to characterize mid-to-high spatial frequency structure on a mirror from early stages of fabrication when slopes may be high and surface irregular, eliminating the need for an extra polishing step before metrology. Working at 9.3um, the system will accept and measure a wide dynamic range of surface characteristics, including roll-off near the edge of the segment. Knowledge of these surface features at the early grinding stage is imperative if characteristics such as mirror edge roll-off are to be minimized. WaveFront Sciences, producer of commercial COAS™ and Columbus™ Shack Hartmann systems, has provided systems engineering and component support for the SSHS system.The SSHS system is based around a special Long Wave Infrared (LWIR) wavefront sensor developed by WaveFront Sciences that is scanned over the mirror surface, making sub-aperture measurements. The smaller, high-resolution measurements are then stitched together to provide high-resolution measurement of the entire mirror surface, even though the surface is in a rough ground state.The system leverages technology from smaller visible instrumentation produced by Wavefront Sciences, especially those for surface sub-aperture measurements of semiconductor wafers. Although the scale of the SSHS is significantly larger than previous applications, substantial commercial technology is directly applicable to the Infrared SSHS with little or no modification. Extensive use was made of existing algorithms for frame stitching and focal spot centroiding. This paper will describe the implementation of the first infrared scanning Shack Hartmann system at Tinsley to address optical fabrication optimization of the JWST Primary Mirror Segments.
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