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Proceedings Paper

Wavefront preserving optics for diffraction-limited storage rings and free-electron lasers
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Paper Abstract

With the advent of Diffraction Limited Storage Rings (DLSR) and the Free Electron Lasers (FEL), the challenge for optical designers is to achieve diffraction-limited spot in the experimental chamber preserving the wavefront. This improvement permits working out of focus with almost uniform beam. To reach this level of quality on the beam, one should go behind the Marechal Criterion, stating that a Strehl Ratio (SR, e.g. the ratio between the intensity on the spot for a perfect optical system and the actual one) of 0.8 is a synonymous of a well performing optic system. In reality, a Strehl ratio in excess of 0.95 is needed for wavefront preserving purposes. This corresponds having long mirrors polished at a precision of better than 1 nm rms. With the initial upgrade of the photon transport system of LCLS we demonstrated that it is possible to have an “almost” perfect beam out of focus putting proper attention to all the details and, aiming for a SR of 0.97. But, besides the high precision shape error, some other details shall be considered. For instance, how many beam sigma one should consider for the specifying his mirror and, also, does the slope errors play any role in the quality of the beam out of focus? Moreover, with the advent of SXR DLSRs, it’s important to understand the requirements for the gratings, behind the shape and slope errors, e.g. on the precision of the groove placement. Also, in this case, the Strehl Ratio is a good way for assessing this problem.

Paper Details

Date Published: 11 September 2019
PDF: 10 pages
Proc. SPIE 11111, X-Ray Lasers and Coherent X-Ray Sources: Development and Applications XIII, 111110G (11 September 2019); doi: 10.1117/12.2531862
Show Author Affiliations
Daniele Cocco, Lawrence Berkeley National Lab. (United States)
SLAC National Accelerator Lab. (United States)
Daniele Spiga, SLAC National Accelerator Lab. (United States)

Published in SPIE Proceedings Vol. 11111:
X-Ray Lasers and Coherent X-Ray Sources: Development and Applications XIII
Annie Klisnick; Carmen S. Menoni, Editor(s)

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