Bent crystals in Laue geometry: dynamical focusing of a polychromatic incident beam

Abstract

The main limitation of Laue geometry for the achievement of a small focus size is the focus broadening caused by the intrinsic Darwin width and the spread of the beam in the Borrmann triangle, resulting from propagation inside the crystal. A method, based on dynamical focusing, is suggested that allows improvement of the quality of high‐energy polychromatic focusing by bent crystals in Laue geometry.

Bent perfect crystals as X-ray focusing polychromators in symmetric Laue geometry

“…Mocella et al (2004Mocella et al ( , 2008 The polychromatic focusing condition (1) can be expressed as R cos B ¼ 2pq=ðp À qÞ, which implies p e ¼ q e ¼ 2pq=ðp þ qÞ. Mocella et al (2004Mocella et al ( , 2008 The polychromatic focusing condition (1) can be expressed as R cos B ¼ 2pq=ðp À qÞ, which implies p e ¼ q e ¼ 2pq=ðp þ qÞ.…”

“…In the design of an energy-dispersive X-ray absorption spectroscopy beamline, one uses a positionsensitive detector downstream of a sample placed in the focal position. According to Mocella et al (2004Mocella et al ( , 2008, the focal size should be minimized when the dynamical and polychromatic foci are made to coincide by the choice of the crystal thickness (see also Sanchez del Rio et al, 1994). The optical performance of such a crystal (polychromator), in particular the size of the focal spot, depends on the crystal thickness via the 'dynamical focusing' effect, which was described decades ago by Afanasev & Kohn (1977) and Aristov et al (1978Aristov et al ( , 1980 in the flat crystal case, and by Kushnir & Suvorov (1982) in the bent crystal case; see also the book by Pinsker (1978).…”

Simulations of x-ray optics for ESRF-upgrade programme

“…However, the absolute limit of crystal focusing in these polychromators would require simulation methods based on the Dynamical Theory that may not be supported by the ray tracing technique. Some works on Dynamical theory have been published [8][9], but a full simulation scenario for micro/nanofocusing with these crystals is being developed. Also, high energy beamline UPBL2 use asymmetric Laue bent crystals and ad-hoc software was used to simulate energy bandwidth and focusing conditions [10], not yet available in ray tracing codes.…”

Spectrometer for hard X-ray free-electron laser based on diffraction focusing

“…It was experimentally confirmed by Aristov et al (1978Aristov et al ( , 1980Aristov et al ( , 1982, and by Koz'mik & Mikhailyuk (1978). Recently the effect of focusing in bent-crystal systems was considered theoretically by Mocella et al (2004Mocella et al ( , 2008, and by Nesterets & Wilkins (2008) as a way for improving polychromatic focusing.…”