29 August 2017 Scanning laser reflection tool for alignment and period measurement of critical-angle transmission gratings
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Abstract
We report progress toward developing a scanning laser reflection (LR) tool for alignment and period measurement of critical-angle transmission (CAT) gratings. It operates on a similar measurement principle as a tool built in 1994 which characterized period variations of grating facets for the Chandra X-ray Observatory. A specularly reflected beam and a first-order diffracted beam were used to record local period variations, surface slope variations, and grating line orientation. In this work, a normal-incidence beam was added to measure slope variations (instead of the angled-incidence beam). Since normal incidence reflection is not coupled with surface height change, it enables measurement of slope variations more accurately and, along with the angled-incidence beam, helps to reconstruct the surface figure (or tilt) map. The measurement capability of in-grating period variations was demonstrated by measuring test reflection grating (RG) samples that show only intrinsic period variations of the interference lithography process. Experimental demonstration for angular alignment of CAT gratings is also presented along with a custom-designed grating alignment assembly (GAA) testbed. All three angles were aligned to satisfy requirements for the proposed Arcus mission. The final measurement of roll misalignment agrees with the roll measurements performed at the PANTER x-ray test facility.
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Jungki Song, Jungki Song, Ralf K. Heilmann, Ralf K. Heilmann, Alexander R Bruccoleri, Alexander R Bruccoleri, Edward Hertz, Edward Hertz, Mark L. Schatternburg, Mark L. Schatternburg, } "Scanning laser reflection tool for alignment and period measurement of critical-angle transmission gratings", Proc. SPIE 10399, Optics for EUV, X-Ray, and Gamma-Ray Astronomy VIII, 1039915 (29 August 2017); doi: 10.1117/12.2274206; https://doi.org/10.1117/12.2274206
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