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6 July 2006 Materials and fabrication issues for large machined germanium immersion gratings
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Abstract
LLNL has successfully fabricated small (1.5 cm2 area) germanium immersion gratings. We studied the feasibility of producing a large germanium immersion grating by means of single point diamond flycutting. Our baseline design is a 63.4° blaze echelle with a 6 cm beam diameter. Birefringence and refractive index inhomogeneity due to stresses produced by the crystal growth process are of concern. Careful selection of the grating blank and possibly additional annealing to relieve stress will be required. The Large Optics Diamond Turning Machine (LODTM) at LLNL is a good choice for the fabrication. It can handle parts up to 1.5 meter in diameter and 0.5 meter in length and is capable of a surface figure accuracy of better than 28 nm rms. We will describe the machine modifications and the machining process for a large grating. A next generation machine, the Precision Optical Grinder and Lathe (POGAL), currently under development has tighter specifications and could produce large gratings with higher precision.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Paul J. Kuzmenko, Pete J. Davis, Steve L. Little, and Layton C. Hale "Materials and fabrication issues for large machined germanium immersion gratings", Proc. SPIE 6273, Optomechanical Technologies for Astronomy, 62732W (6 July 2006); https://doi.org/10.1117/12.670534
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