Diamond Annual Review 2023/24

66 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 3 / 2 4 height error with rms slope error below 100 nrad is a crucial milestone for the Diamond IBF instrument. The next step is to deliver the same surface quality on samples over 100 mm in size, thus making possible the provision of high- quality beamline optics. Newmultilayer fabrication facility Multilayer monochromators, gratings, and soft X-ray polarimeters are now employed at many synchrotron X-ray beamlines. They can enhance the reflectivity of tender X-ray optics and provide high-aperture mirrors for nanofocusing. Both these applications are in demand for Diamond-II. An in- line multilayer deposition system has been built at Diamond (Figure 5). It is the only one of its kind in the UK, and it will allow advanced and specialised optical elements, including laterally graded and depth-graded multilayers, to be fabricated rapidly. The instrument is engineered to produce both single and multilayer coatings on mirrors up to 1,000 mm long using eight rectangular cathodes. In-situ diagnostic tools measure the thickness uniformity and stress of the coating. Annealing up to 700°C is possible within the load lock chamber. Pumpdown, deposition, and venting are all automated. The power of the sputtering source, the working pressure, and the motor positions are automatically archived. Remarkable lateral film thickness uniformity, with variation as low as 0.06% along the translation direction, was achieved during commissioning. This new fabrication facility is now poised to fabricate periodic, laterally graded and depth-graded multilayers. It will cater to both hard and soft X-ray beamlines that serve diverse scientific applications at Diamond. X-ray topography The Optics and Metrology group and the B16 beamline team have built up an X-ray topography program that inspects diffracting crystal optics for both external and internal users. This year’s external users have come from both academic and industrial organisations. X-ray topography serves Diamond as an at-wavelength metrology technique that supplements the OML’s visible-light measurements of surface figure and roughness. Because B16 can admit either white or monochromatic beam, it offers many topographic techniques. Surface scratches and pits, lattice distortions within the bulk and long-range strains caused by clamping have all been measured in the crystal samples of the past year. Samples can be oriented in any direction. It is now possible to measure the evolution of a crystal’s strain“live”as the temperature varies (Figure 6). Alvarez X-ray zoom lens An Alvarez varifocal X-ray lens has been developed and demonstrated at B16 by Optics and Metrology group scientists. This work presents the first demonstration of an Alvarez lens in the X-ray regime which adaptively corrects defocus and astigmatism aberrations of X-ray optics. An Alvarez lens consists of two refractors with a cubic surface profile that are placed one behind the other (Figure 7) . Together they apply a parabolic perturbation to the wavefront that varies as they are shifted transversely by equal but opposite amounts. Therefore, when inserted into a beamline that focuses the beam, an Alvarez Figure 6: Strain relaxation across the centre of a clamped sample crystal during warming from liquid-nitrogen temperature (a) at 83.5 K (b) at 110.2 K. Strain is in µrad (see colour bar) and positions are in mm. Figure 7: Schematic of an Alvarez X-ray zoom lens used in conjunction with a vertically focusing mirror (VKB) at B16. Figure 8: Theoretical plot of critical power (solid curve) with power and power density on DCM 1st crystals at various Diamond beamlines (individual points). FEA showed acceptable deformation at blue points, and unacceptable deformation at orange and red points. X-ray technologies