Diamond Annual Review 2021/22

110 111 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 1 / 2 2 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 1 / 2 2 Optics andMetrology Group Kawal Sawhney, Optics andMetrology Group Leader T he Optics & Metrology (O&M) group continues to provide expert operational support to all beamlines of Diamond Light Source and is actively involved in designing upgraded and new flagship beamlines for Diamond-II. An extensive research and development programme within the O&M group is underway to investigate the optical challenges posed by Diamond-II. This now includes establishing in-house X-ray optic fabrication facilities. The Optics Fabrication Building (OFB) is under construction and will house Diamond’s Multilayer Fabrication Facility, the only one in the UK. Development of metrology hardware is also progressing to enable measurement of the enhanced-quality X-ray mirrors needed for Diamond-II. The new technique of laser Speckle Angular Measurement (SAM), developed by our group, enables slope errors of X-ray mirrors to be characterised in two dimensions with nanoradian resolution. Laser interferometry in collaboration with the National Physical Laboratory (NPL) has measured 0.5 nrad angular steps of Diamond’s Nano-Angle Generator. The synergy of fabrication and state-of-the-art metrology will stimulate optical developments at Diamond which cannot be made elsewhere in the UK. Over the next few years, Diamond will join other synchrotrons around the world in upgrading its storage ring. The Diamond-II project will yield brighter X-ray beams but will also require substantial changes to the layout of many beamlines. The Optics & Metrology Group continues to provide optical designs and calculate power loads for current beamlines and the three new flagship beamlines: SWIFT (spectroscopy), K04 (XChem fragment screening project), and CSXID (Coherent Soft X-ray Imaging and Diffraction). The Optical Metrology Laboratory (OML) will be moved to a new site to accommodate CSXID at straight 17. Theoretical modelling tools have been developed to predict the temperature distribution and surface distortion under X-ray beam of cryo-cooled monochromator crystals. Other theoretical developments include: a new type of Ptychography that can determine the aberrations of an optical component using a partially coherent X-ray beam 1 ; and demonstration of a new imaging technique that records phase variation in all directions simultaneously 2 . Multilayer optics fabrication facility Diamond has until now depended on commercial vendors to provide X-ray Technologies at Diamond I t is self-evident that in order for our instruments to produce world-leading science, we need to have world-class optics, detectors and computing technologies at our fingertips; technological advances never stop but are continually evolving. This section describes the support and advances in the Optics andMetrology Group, Detector Group and Scientific Software Controls and Computation department at Diamond Light Source. Advances which are supporting and enhancing our capabilities today are described, but also developments that will keep us competitive over the next few years. These groups are very active in calculations and specifications for beamlines and instruments being put forward and planned for Diamond-II, an integrated upgrade of the synchrotron, beamlines and computational facilities. The pandemicmay have slowed some developments andmade it harder towork physically alongside our colleagues, but it has also opened opportunities for remote operation for staff, users and collaborators. These advances continue to keep us competitive worldwide, and Diamond is proud to be at the forefront of many of these technologies. X-ray Technologies X-ray optics. However, many types of optics are manufactured by only a few suppliers, in some cases only a single vendor, making Diamond vulnerable to supply disruptions and limiting the flexibility to order bespoke optics for highly specialised applications. In-house manufacturing capabilities will help Diamond to meet these challenges, and to manufacture niche optics that are not commercially available. This will become increasingly important as Diamond-II progresses. Finally, the fabrication facilities will enable a new generation of young scientists and engineers to be trained in the UK. In October 2021, construction began on the new Optics Fabrication Building (OFB) outside Zone 4 (Fig. 1). It will house Diamond’s new Multilayer Fabrication Facility, the first of its kind in the UK. This new facility will deposit highly uniform multilayers on substrates up to 1000 mm long. Multilayer optics have already proven their worth at several Diamond beamlines by acting as monochromators capable of providing two orders of magnitude more flux than traditional double-crystal monochromators, whilst maintaining energy resolution of ~ 1%. They have enabled focusing of X-rays up to 76 keV at I15- 1, where standard mirrors struggle to reflect X-ray efficiently above 25 keV. Further applications of multilayer optics are expected in macromolecular crystallography, nano-tomography and fluorescence microscopy. Completion of the OFB is scheduled for August 2022, after which the Multilayer Fabrication Facility will be installed, commissioned and optimised by summer 2024. Nano-precisionmirror metrology Upcoming diffraction-limited storage rings like Diamond-II are already creating demand for X-ray mirrors shaped to an even higher accuracy than achieved by today’s most advanced manufacturing techniques. Meeting this demand will require metrology instruments of increased speed and precision, which ideally are cost effective and do not compete with user experiments for X-ray access to beamlines. In the OML, a novel Speckle Angular Measurement (SAM) instrument for measuring a mirror’s figure has been installed on the Diamond-NOM gantry (Fig. 2) 3 . A laser beam collimated by a lens is scattered by a diffuser, which introduces a two-dimensional speckle pattern. Variations of the sagittal and tangential slope, at each position on the mirror illuminated by the laser, will shift the speckle pattern as recorded by the camera. Precise tracking of the speckle displacements as the laser is scanned along the mirror’s surface yields a two-dimensional map of the mirror’s slope. An advanced sub- pixel algorithmenables slopemeasurements on the nanoradian level. The SAM technique thus adds two-dimensional capabilities to a one-dimensional slope profiler at low cost and in little space. Results are in good agreement with the OML’s Fizeau interferometer. The SAM instrument can also measure strongly curved surfaces (radius < 0.5 m) beyond the curvature range of the Diamond- NOM. Not only synchrotrons and XFELs, but also astronomical telescopes, can benefit from this technique. Partnering with NPL to inspect nano-positioning motion stages Accurate nano-positioning of samples and X-ray optics will become increasingly important for Diamond’s beamlines. Yet without careful calibration and correction, many commercial nano-positioning devices do not meet beamlines requirements. Common problems include vibrations, parasitic motions, temperature drifts, control issues and misalignment between the components of composite stacks of motion stages. Successful commissioning of nano-positioning systems requires a calibrating stage that makes accurate, reproducible motions on the nanoradian level, and instruments capable of measuring these extremely small motions. Thanks to a collaboration with the National Physical Laboratory (NPL), both components are now in operation in Diamond’s Precision Metrology Laboratory (PML), which characterises motion stages for Diamond’s beamlines. Diamond previously developed the Nano- Angle Generator (NANGO), a flexure-based, piezo-actuated stage capable of precise angular motions from milliradians down to nanoradians. NANGO is used to calibrate metrology instruments by rotating a reference optic through known angles. NPL contributed a dual-beam laser interferometer with a 200 kHz acquisition rate. This is far above the 25 Hz acquisition rate of a digital autocollimator and makes dynamic behaviour observable. The interferometer is composed of a rotatable part, which is mounted on the NANGO rotary stage, and a fixed part. The NPL interferometer has demonstrated that NANGO can make distinct steps of 500 picoradians, sinusoidal oscillations at 0.4 Hz with an amplitude down to 125 picoradians, or 1 nanoradian oscillations at 40 Hz. Plans are being made to construct a three- or four-beam version of the NPL interferometer for simultaneous measurement of orthogonal angles and translations. The combination of Diamond’s NANGO and the NPL’s interferometer has produced a state-of-the-art system at the forefront of nanometrology for the synchrotron and XFEL community. References: 1. Moxham, T. E. J. et al. Aberration characterization of x-ray optics using multi-modal Ptychography and a partially coherent source. Appl. Phys. Lett. 118, 104104 (2021). DOI: 10.1063/5.0041341 2. Wang, H. et al. Hard X-ray omnidirectional differential phase and dark-field imaging. PNAS 118 , e2022319118 (2021). DOI: 10.1073/ pnas.2022319118 3. Wang, H. et al. Nano-precision metrology of X-ray mirrors with laser speckle angular measurement. Light: Science & Applications 10, 195 (2021). DOI: 10.1038/s41377-021-00632-4 Figure 1: Artist’s conception of Diamond’s Optics Fabrication Building. Figure 2: Setup for speckle angular measurement (SAM) on the Diamond-NOM gantry. “SUT” indicates the surface under test.