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X-ray beam expansion by the application of re-entrant surface profiles to deformable bimorph mirrors

DOI: 10.1117/12.2239116 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: Conference Paper
Conference: SPIE 9965: Adaptive X-ray Optics IV
Peer Reviewed: No

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

Open Access Open Access

Abstract: Deformable, piezo bimorph mirrors are often used to expand X-ray beams to a continuous range of sizes. However, optical polishing errors present on all X-ray mirrors introduce striations into the reflected beam. To counteract them, reentrant surface modifications with alternating concave and convex curvature have been proposed and applied to mirrors of fixed shape or bimorph mirrors. For the latter, a new method of constructing re-entrant surface modifications on segments of unequal length is described. This allows the re-entrant modification required for a desired beam size at the focal point to be matched to the bimorph mirror’s polishing errors, thus reducing the voltage variations. Optical profilometry using the Diamond-NOM showed that a 5-segment and a 7-segment modification could be suitably applied to a deformable bimorph mirror. X-ray tests showed that striations caused by the 5-segment modification in the beam at the focus are concentrated at the beam edges, while the beam center is left clear. This is in contrast to simple defocusing, in which a strong side shoulder appears. The 7-segment modification produces a pattern of evenly spaced striations. The intensity spikes seen with the re-entrant modifications are caused chiefly by the finite curvature of the mirror at the turning points. The question of whether deformable bimorph mirrors with different piezo response functions could sharpen the curvature changes will be investigated. Optimal modifications of continuous curvature, which could more realistically be applied, will be sought.

Journal Keywords: X-ray, mirror, bimorph, surface, profile

Subject Areas: Technique Development, Physics

Diamond Offline Facilities: metrology lab
Instruments: B16-Test Beamline


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