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Creating flat-top X-ray beams by applying surface profiles of alternating curvature to deformable piezo bimorph mirrors

DOI: 10.1107/S1600577516013308 DOI Help

Authors: John P. Sutter (Diamond Light Source) , Simon G. Alcock (Diamond Light Source) , Yogesh Kashyap (Diamond Light Source) , Ioana Nistea (Diamond Light Source) , Hongchang Wang (Diamond Light Source) , Kawal Sawhney (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Synchrotron Radiation , VOL 23 , PAGES 1333-1347

State: Published (Approved)
Published: November 2016
Diamond Proposal Number(s): 3803 , 13515

Open Access Open Access

Abstract: Beam shaping is becoming increasingly important for synchrotron X-ray applications. Although routine for visible light lasers, this is challenging for X-rays due to the limited source coherence and extreme optical tolerances required for the shaping mirrors. In deliberate defocusing, even surface errors <5 nm r.m.s. introduce damagingly large striations into the reflected beam. To counteract such problems, surface modifications with alternating concave and convex curvature on equal segments were polished onto the surface of nonactive mirrors of fixed curvature. Such optics are useful for providing a fixed size of X-ray beam, but do not provide the adaptability required by many experiments. In contrast, deformable piezo bimorph mirrors permit a continuous range of X-ray beam sizes and shapes. A new theory is developed for applying non-periodic modifications of alternating curvature to optical surfaces. The position and length of the segments may be freely chosen. For the first time, surface modifications of alternating curvature are applied to bimorph mirrors to generate non-Gaussian X-ray beam profiles of specified width. The new theory’s freedom is exploited to choose the segments to match the polishing errors of medium wavelength (>10 mm) and the piezos’ influence on the mirror’s figure. Five- and seven-segment modifications of alternating curvature are calculated and verified by visible light and X-ray metrology. The latter yields beam profiles with less striation than those made by defocusing. Remaining beam striations are explained by applying geometrical optics to the deviations from the ideal surface modifications of alternating curvature.

Journal Keywords: X-ray; bimorph; mirror; beam shaping; re-entrant

Subject Areas: Technique Development, Physics, Engineering

Instruments: B16-Test Beamline

Added On: 27/10/2016 17:21

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