Diamond Annual Review 2019/20

98 99 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 1 9 / 2 0 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 1 9 / 2 0 Figure 1: IBF system designed and developed in-house: external (left) and internal (right) views. surface and carefully controlled removal of material to produce the desired mirror shape. A new in-house designed IBF system has recently been developed by the Optics Group to bring high-precision optics finishing capability to Diamond (Fig.1). A DC gridded ion source is paired with a set of apertures to produce a shaped ion beam which erodes the mirror surface as it is moved past by a 4-axis motion system. 'Malcolm' continuous scanning software, previously developed at Diamond, provides precise control of the dwell time at each location on the optical surface to ensure the correct material removal profile is achieved. Onboard optical metrology will allow for rapid surface measurement feedback and is complemented by a wide range of optical and X-ray metrology tools provided by OML and B16. The IBF system is currently in the early stages of commissioning and calibration, but it is ultimately expected to provide extremely high-quality finishing of mirrors within a much shorter timeframe than can currently be achieved. This capacity for rapid development and testing of mirrors greatly increases the feasibility of novel designs such as multi-lane mirrors and other complex mirror shapes like aspheres. Adaptable refractive correctors: a new optical device for extreme focusing of X-rays High-quality mirrors and lenses are commonly used at X-ray beamlines to focus the X-ray beam into small (sub-1 micrometre) focal spots allowing materials to be studied with high spatial resolution. The design and manufacture of X-ray optical elements is highly specialised and at this level, any small imperfections cause the intensity distribution of the focal spot to be spoiled. The Optics Group have devised a new type of optical element that is able to dynamically correct for the effect of the imperfections by applying a spatially dependent phase shift to the wavefront of the focused X-rays 1 . The new element is known as an “adaptable refractive corrector”. The device consists of two phase plates fabricated with a special thickness profile that apply a phase correction to the X-rays as shown in Fig. 2. The phase correction can be varied in form and size by independent adjustment of the positions of the two phase plates, allowing the correction to be adapted to compensate for the unique effect of imperfections in optical elements. A single design of adaptable refractive corrector could be used on different beamlines and with different optical elements to compensate for X-ray wavefront errors. A device was manufactured using microfabrication techniques and was then used on B16 to test a variety of mirror and lenses. A sensitive technique was used to measure the X-ray wavefront, to determine the X-ray phase error at the optical element and to allow the adaptable corrector to be optimised. The measurements showed that after optimisation of the corrector, the effect of the imperfections in the optical elements was reduced by a factor of up to 7. A further experiment was carried out on the X-ray Imaging and Coherence beamline (I13) in which the adaptable corrector was used to overcome the imperfections of an elliptical focusing mirror. The highly coherent X-ray beam allowed us to achieve a focused beam size after correction of 70 nm, which is close to the theoretical diffraction limit. This demonstrates that such optics will be essential to exploit the planned low-emittance Diamond-II upgrade and future low-emittance X-ray sources elsewhere worldwide. References 1. Laundy, D. et al. Adaptable refractive correctors for x-ray optics. Optica 6 , 1484-1490, (2019). DOI:10.1364/OPTICA.6.001484 2. Wang, H. et al. High-energy, high-resolution, fly-scan X-ray phase tomography. Scientific Reports 9 , 8913, (2019). DOI:10.1038/s41598-019-45561-w 3. Hand, M. et al. Ion beam figuring and optical metrology system for synchrotron x-ray mirrors. Proc. SPIE 11109, Advances in Metrology for X-ray and EUV Optics VIII 111090A (2019). DOI: 10.1117/12.2528463 4. Sutter, J. P. et al. 1 m long multilayer-coated deformable piezoelectric bimorph mirror for adjustable focusing of high-energy X-rays. Opt. Express 27 , 16121-16142, (2019). DOI:10.1364/OE.27.016121 5. Nistea, I.-T., et al. Controlling an active bimorph deformable mirror with sub-nanometre resolution. Proc. SPIE SPIE 11109, Advances in Metrology for X-ray and EUV Optics VIII 111090E (2019). DOI: 10.1117/12.2529322 6. Nistea, I.-T., et al. The Optical Metrology Laboratory at Diamond: pushing the limits of nano-metrology. Proc. SPIE SPIE 11109, Advances in Metrology for X-ray and EUV Optics VIII 1110906 (2019). DOI: 10.1117/12.2529401 Optics andMetrology Group Figure 2: Schematic showing the adaptable corrector with a double mirror system. Optics andMetrology Group Kawal Sawhney, Optics andMetrology Group Leader T he Optics and Metrology Group is guiding Diamond Light Source and other facilities with state-of-the-art capabilities 1-6 , which it continues to expand. For current upgrades and Diamond-II, we are enhancing our techniques for simulation, manufacturing and measurement. Our new ion beam figuring system will allow rapid manufacture of complex, precise mirrors. Novel adaptable refractive correctors are boosting the effectiveness of nano-focusing optics. Ex situ measurements of vibration and positional accuracy are being brought to 50 nrad and nm precision. X-ray topography is now a standard tool for detecting micron-sized surface defects on crystals. The versatile optics Test Beamline (B16) continues to support all these efforts while running a well-subscribed program of external user experiments. These advances continue to keep Diamond competitive worldwide. The Optics Metrology Lab (OML) and the Precision Metrology Lab (PML) continue to provide high quality testing of beamline X-ray optics and motion systems. Both labs provide a valued service to help assemble, install, and pre- commission major beamline components, thereby improving the scientific output of all beamlines. To remain competitive with other facilities around the world, many beamlines are now actively upgrading their optics and motion stages, including: crystal monochromators with angular vibrations less than 50 nrad rms; X-ray mirrors with slope errors better than 100 nrad rms; and micro- and nano-positioning stages with nm level parasitic errors.To keep one step ahead of such developments, the OML and PML are both embarking on a series of innovative research and development projects. The aim is to improve the accuracy of Diamond’s metrology instruments and analysis algorithms for measuring distances, angles, and vibrations. To enhance these activities, collaborations have been developedwith national metrology institutes such as the UK’s National Physical Lab and the Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute in Germany. Monochromatic X-ray topography is now a standard technique available on B16 for inspecting crystal surfaces for micron-size defects. Surface quality can be measured over large areas on test crystals facing up, down or sideways depending on the required mount. White-beam topography is also possible. Topography helped us lead the development of monochromator crystals for the Dual Imaging And Diffraction (DIAD) imaging branch through several trials to success. We are now providing X-ray topography not only to Diamond, but also to commercial users. Our in-house capability ensures that new crystals are fit for purpose at installation. The planned Diamond-II upgrade brings opportunities and challenges for beamline optics, requiring upgrades to match evolving needs and emerging opportunities in several scientific and technical areas. The Optics & Metrology group is performing extensive optics simulations and optimisation of sources for all beamlines given the new machine characteristics, the analysis and mitigation of thermal load effects on optics, and developing additional metrology capabilities to test high-quality optics. Specifically, this includes a further enhancement of our world-class in-house metrology facility to enable X-ray optics of ~50 nrad rms slope error to be reliably measured and characterised as well as at-wavelength metrology (i.e. using X-rays) complemented with simulations, to allow the development of procedures for fast, automatic optics alignment and for compensation of drift and beam vibrations. The work started a few years ago and will continue throughout the Diamond-II project. Ion beamfiguring (IBF) system Meeting the X-ray beam performance demands of Diamond’s beamlines (in terms of micro/nano-focusing, extreme energy resolution, high coherence, etc.) necessitates the use of mirrors with an ultra-high-quality surface finish, with the most demanding applications requiring deviations from the ideal surface profile of less than 1 nm rms. In the final stages of manufacturing such mirrors, deterministic polishing methods such as ion beam figuring (IBF) are often used. These techniques employ precise measurements of the optical Autocollimator Motion stages