Diamond Annual Review 2020/21

118 119 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 0 / 2 1 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 0 / 2 1 Optics andMetrology Group Kawal Sawhney, Optics and Metrology Group Leader O ver the past year, the Optics and Metrology Group has remained active despite the year’s access restrictions and has continued to provide a full range of services to Diamond’s beamlines, whilst expanding its own capabilities. This includes work on optics designs for current and new flagship beamlines to take the fullest advantage of Diamond-II, metrology testing in the Optics and Precision Metrology labs, and optics R&D projects 1-5 on the B16 Test beamline. A new Optics Fabrication Building that will house a state-of-the-art multilayer deposition laboratory is being designed. Optics design for Diamond-II Design and feasibility studies for beamline optics on Diamond-II have been ongoing since 2015. A lattice based on a Modified-Hybrid 6 Bend Achromat structure will reduce horizontal electron beam emittance to about 1/20 of its current value. Smaller and more collimated photon sources will produce nearly round beams. The increase in electron beam energy from 3 GeV to 3.5 GeV will enhance brightness and flux, as will new insertion devices on several beamlines. Outlines and advanced optical designs have been prepared for flagship beamline proposals. These show that the planned instruments for spectroscopy, coherent imaging, nano-Angle-Resolved Photoemission Spectroscopy (ARPES), Macromolecular Crystallography (MX) and coherent soft X-ray scattering will be highly competitive, and they formed a core part of the flagship proposals presented by Diamond Science Group Leaders to the Diamond scientific advisory panels. Some of the current bending magnet beamlines will be equipped with new source types such as three-pole wigglers. The possibility that radiation from the different magnets will interfere was investigated and it was shown that the new emittance of Diamond-II will not degrade the performance of any of the wiggler beamlines. The higher ring energy and new undulators will increase the power load on the X-ray optics. The impact on the temperature distribution and deformation of several double crystal monochromators has been assessed by a simple, intuitive model that adds physical insights to more accurate finite element analysis (FEA) simulations. This model predicts critical power levels below which the crystal deformation remains acceptable. Monochromators will be kept below this threshold by using slits, filters, or cooling. Upgrades to Optics Metrology instruments Diamond’s Optics Metrology Lab (OML) is well equipped with a suite of high-quality metrology instruments. Over the years, hundreds of X-ray mirror systems have been measured for all Diamond beamlines. Recently, the Diamond-Nanometre Optical Metrology (NOM) slope-measuring profiler has been upgraded with a 10x faster autocollimator, a more sophisticated motion controller, an automated pitch stage for remote working and reduced downtime, and better motion synchronisation and data capture through the Experimental Physics and Industrial Control System (EPICS). The reduction of systematic errors has created a faster, more accurate Diamond-NOM. Similarly, the Zygo HDX Fizeau interferometer has been upgraded with a stitching system developed in-house (Fig. 1). A Fizeau interferometer images only a small portion of the surface of an X-ray mirror in a single shot. However, with motion stages that translate and rotate the mirror, a series of overlapping images is captured. Stitching these images together produces a panoramic view of the entire optical surface. This process has been automated by Python scripts written by the OML team. The upgraded Diamond-NOM and HDX agree almost perfectly on a state- of-the-art mirror from JTEC (a manufacturer of X-ray mirrors for synchrotron facilities) that deviates from the ideal elliptical surface by a slope error of < 50 nrad rms (Fig. 2) and a height error of < 1 nm peak-to-valley. This gives confidence for measuring the next-generation X-ray optics required for Diamond-II. Overcoming partial coherence withmulti- modal ptychography for wavefront sensing The quality of the X-ray beam delivered to samples depends strongly on the fabrication and alignment of the optics which transport it. Accurate characterisation of errors is essential for correction and is best performed in situ at the optics’ designed wavelength. Ptychography is a scanning coherent diffraction imaging technique capable of accurately recovering the two- dimensional complex sample and probe functions with high spatial resolution. It is normally used by high-coherence undulator beamlines such as I13, but 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 has been developed by the Optics Group as an imaging and wavefront sensing technique using partial coherence on B16. Ptychography applies iterative phase retrieval to diffraction patterns from overlapping sample positions. Blurring of the diffraction patterns caused by partial coherence is treated by modelling the sample or probe as a sum of coherent multi-modal states.The reconstruction algorithmdoes not determine which one is causing loss of coherence, but a coherent probe reconstruction is possible if the loss of coherence is ascribed to the sample, even though in reality it is the beam that is partially coherent (Fig. 3). The technique has been demonstrated for a wide range of X-ray focusing optics and has been validated with other wavefront sensing techniques. Additionally, the method has extended the imaging capabilities of B16 to a resolution of 100 nm over extended samples. This work paves the way for synchrotron beamlines to offer nanoscale imaging and optics characterisation without special coherent sources or expensive optics upgrades. References: 1. Dhamgaye V. et al. Correction of the X-ray wavefront from compound refractive lenses using 3D printed refractive structures. J. Synchrotron Radiat. 27, 1518–1527 (2020). DOI: 10.1107/S1600577520011765 2. Moxham T. E. J. et al. Hard X-ray ptychography for optics characterization using a partially coherent synchrotron source. J. Synchrotron Radiat. 27, 1688–1695 (2020). DOI: 10.1107/S1600577520012151 3. Hu L. et al. Fast convolution-based performance estimation method for diffraction-limited source with imperfect X-ray optics. J. Synchrotron Radiat. 27, 1539–1552 (2020). DOI: 10.1107/S1600577520012825 4. Sutter J. P. et al. Bragg-case x-ray dynamical diffraction propagator in SRW: application to thin crystal phase retarders. in Proc.SPIE 11493, 114930V (2020). DOI: 10.1117/12.2567341 5. Hu L. et al. Perturbation perspective of partial coherence discussion on imperfect x-ray optical elements. in Proc.SPIE 11493, 114930D (2020). DOI: 10.1117/12.2567207 Figure 1: Murilo De Bazan, Metrology Scientist, with the Fizeau interferometer stitching system built at Diamond. -50 -25 0 25 50 -150 -75 0 75 150 Slope Error < 50 nrad rms Slope Error [nrad] Mirror Length [mm] Diamond-NOM HDX Interferometer Figure 2: Near-perfect agreement between the upgraded Diamond-NOM and the HDX Fizeau stitching system for an elliptically curved mirror with a slope error < 50 nrad rms. Figure 3: Coherent and partially coherent propagations of the reconstructed probe using multi- modal ptychography with a beryllium compound refractive lens.