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![[Figure 3]](vl5005fig3mag.jpg)
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Figure 3
Examples of bi-curved crystal analysers having a support parallel or slightly inclined to the diffraction planes and operating in reflection mode. (a) Photograph of such a system having a `plan + circular' profile of graphite (002) planes and tested with a Cu Kα1 X-ray source; beam paths are in green (Hodeau et al., 2008  ). (b) Example of a diffraction pattern collected by this system on a Maya fresco painting, without (blue) and with (black) diffraction filtering: the diffuse background filtered by the cone is ∼30 times weaker than the unfiltered one, while the amplitude of the (104) diffracted peak of the calcite filtered by this graphite (002) analyser is only about three times weaker than the unfiltered one; thus with this diffraction filtering, the signal-to-noise ratio is much better and the fluorescence is suppressed, allowing clean diffraction patterns of this heterogeneous sample to be collected. (c) Realization of the MAD analyser in reflection mode, having a double `logarithmic-spiral + circular' profile, by using a 3D printed LogSpiral support with a 0.5 mm graphite (002) sheet glued on this curved surface. (d) 3D scheme of such a MAD system having a `LogSpiral + circular' profile: this figure shows beam paths on this bi-curved analyser having a crystalline graphite mosaic layer (002) optimized for filtering Cu Kα1 X-ray radiation. In this example the sample-to-detector distance is 170 mm and the radial width used on the MAD system is chosen to be 33 mm or 115 mm: this increase in the usable dimension of such a system increases its angular filtering acceptance from 5° (dark green lines) to 20° (dark brown lines) and the width of the readout band on the 2D detector (from 1 to 15 mm); it should be noted that this band is very thin (<1 mm) for an angular acceptance of 5° (Hodeau et al., 2008). (e) Example of the 14-crystal Si(111) spherical plate spectrometer (having 500 µm thin sheets of glued single crystal) developed on the ESRF FAME-UHD line; this spectrometer is dedicated to accurate fluorescence detection; the beams filtered by each analyser (as seen by green lines for one diffraction plane) have a rather large width which is related to the size/geometry of its support dish and allows the filtering efficiency to be increased (Hazemann et al., 2009; Llorens et al., 2012; Proux et al., 2017). |
![[Figure 3]](vl5005fig3.jpg)
 | JOURNAL OF SYNCHROTRON RADIATION |
ISSN: 1600-5775
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