Characterization of a bent Laue double-crystal beam-expanding monochromator

Abstract

A bent Laue double-crystal monochromator system has been designed for vertically expanding the X-ray beam at the Canadian Light Source's BioMedical Imaging and Therapy beamlines. Expansion by a factor of 12 has been achieved without deteriorating the transverse coherence of the beam, allowing phasebased imaging techniques to be performed with high flux and a large field of view. However, preliminary studies revealed a lack of uniformity in the beam, presumed to be caused by imperfect bending of the silicon crystal wafers used in the system. Results from finite-element analysis of the system predicted that the second crystal would be most severely affected and has been shown experimentally. It has been determined that the majority of the distortion occurs in the second crystal and is likely caused by an imperfection in the surface of the bending frame. Measurements were then taken to characterize the bending of the crystal using both mechanical and diffraction techniques. In particular, two techniques commonly used to map dislocations in crystal structures have been adapted to map local curvature of the bent crystals. One of these, a variation of Berg-Berrett topography, has been used to quantify the diffraction effects caused by the distortion of the crystal wafer. This technique produces a global mapping of the deviation of the diffraction angle relative to a perfect cylinder. This information is critical for improving bending and measuring tolerances of imperfections by correlating this mapping to areas of missing intensity in the beam.

X-ray focusing by bent crystals: focal positions as predicted by the crystal lens equation and the dynamical diffraction theory

“…As pointed out by Chukhovskii & Krisch (1992), the monochromatic focusing condition must not be confused with the polychromatic focusing condition (Matsushita & Hashizume, 1983;Caciuffo et al, 1987;Schulze et al, 1998;Martinson et al, 2015Martinson et al, , 2017, obtained by varying the wavelength of the reflected rays in order to satisfy the exact Bragg condition on the whole crystal surface. The equation ' 0 + ' h = 2 in the Laue case, or ' 0 + ' h = 2 + in the Bragg case, implies Á' 0 + Á' h = 0.…”

Determination of the Exact Orientation of Single-Crystal X-ray Optics from Its Glitch Spectrum and Modeling of Glitches for an Arbitrary Configuration

“…This method can be more technically demanding, especially in terms of achieving a very precise surface shape, a low surface roughness, and low subsurface damage [12]. If this is not achieved, the uniformity of the beam may decrease [13].…”

Structure, stress and optical properties of Cr/C multilayers for the tender X-ray range

“…Over the last several decades, single-layer coating gratings and crystal monochromators have demonstrated excellent performance at synchrotron radiation sources in the soft and hard X-ray energy ranges (Pascarelli et al, 1996;Underwood & Gullikson, 1998;Hua et al, 2016;Martinson et al, 2017). However, in the gap range (1-4 keV), also called the 'tender X-ray range', where the K absorption edges of P, S, Cl and some 3d transition metals as well as the L absorption edges of 4d transition metals are located, crystal monochromators have to operate at near normal incidence because of the small dspacing, which causes a significantly increasing power density leading to serious heat-load problems (Cowan et al, 1989).…”