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Synchrotron light sources require X‐ray optics with extremely demanding accuracy for the surface profile, with less than 100 nrad slope errors and sub‐nanometre height errors. Such errors are challenging to achieve for aspheres using traditional polishing methods. However, post‐polishing error correction can be performed using techniques such as ion beam figuring (IBF) to improve optics to the desired quality. This work presents a brief overview of the history of IBF, introduces some of the challenges for obtaining such demanding figure errors, and highlights the work done at several in‐house IBF facilities at synchrotron light sources worldwide to obtain state‐of‐the‐art optical quality. [ABSTRACT FROM AUTHOR]

Ion beam figuring (IBF) is a powerful technique for figure correction of X‐ray mirrors to a high accuracy. Here, recent technical advancements in the IBF instrument developed at Diamond Light Source are presented and experimental results for figuring of X‐ray mirrors are given. The IBF system is equipped with a stable DC gridded ion source (120 mm diameter), a four‐axis motion stage to manipulate the optic, a Faraday cup to monitor the ion‐beam current, and a camera for alignment. A novel laser speckle angular measurement instrument also provides on‐board metrology. To demonstrate the IBF system's capabilities, two silicon X‐ray mirrors were processed. For 1D correction, a height error of 0.08 nm r.m.s. and a slope error of 44 nrad r.m.s. were achieved. For 2D correction over a 67 mm × 17 mm clear aperture, a height error of 0.8 nm r.m.s. and a slope error of 230 nrad r.m.s. were obtained. For the 1D case, this optical quality is comparable with the highest‐grade, commercially available, X‐ray optics. [ABSTRACT FROM AUTHOR]

The I21 beamline at Diamond Light Source is dedicated to advanced resonant inelastic X‐ray scattering (RIXS) for probing charge, orbital, spin and lattice excitations in materials across condensed matter physics, applied sciences and chemistry. Both the beamline and the RIXS spectrometer employ divergent variable‐line‐spacing gratings covering a broad energy range of 280–3000 eV. A combined energy resolution of ∼35 meV (16 meV) is readily achieved at 930 eV (530 eV) owing to the optimized optics and the mechanics. Considerable efforts have been paid to the design of the entire beamline, particularly the implementation of the collection mirrors, to maximize the X‐ray photon throughput. The continuous rotation of the spectrometer over 150° under ultra high vacuum and a cryogenic manipulator with six degrees of freedom allow accurate mappings of low‐energy excitations from solid state materials in momentum space. Most importantly, the facility features a unique combination of the high energy resolution and the high photon throughput vital for advanced RIXS applications. Together with its stability and user friendliness, I21 has become one of the most sought after RIXS beamlines in the world. [ABSTRACT FROM AUTHOR]

Piezoelectric bimorph deformable mirrors ('bimorphs') are routinely used on many synchrotron and free‐electron laser beamlines to provide active variation in the size and shape of the X‐ray beam. However, the time‐domain potential of such optics has never been fully exploited. For the first time, the fast dynamic bending response of bimorphs is investigated here using Fizeau interferometry. Automated scripts for acquisition and analysis were developed to collect Fizeau data at a rate of 0.1 Hz to record dynamic changes in the optical surface as voltages were applied to the electrodes of the piezoelectric actuators. It is demonstrated that residual drift in the tangential radius of curvature of a bimorph can be significantly reduced using enhanced opto‐mechanical holders and a fast programmable high‐voltage power supply. Further improvements are achieved by applying small opposing voltages to compensate for piezoelectric creep. The present study shows that bimorphs can truly be used as high‐speed adaptive optics for the X‐ray domain, even without closed‐loop feedback correction. This opens the possibility for relatively simple real‐time tuning of the profile of X‐ray bimorphs. Part II of this study [Alcock, Nistea, Signorato, Owen, Axford, Sutter, Foster & Sawhney (2019), J. Synchrotron Rad.26, 45–51] builds upon these results and demonstrates how bimorphs can rapidly provide customisable sizes and shapes of synchrotron X‐ray beams, specifically tailored to suit the experimental samples being investigated. The time‐domain bending behaviour of piezoelectric bimorph deformable X‐ray mirrors for use at synchrotron and X‐ray free‐electron laser sources is investigated for the first time using high‐speed Fizeau interferometry. It is demonstrated that several hardware and software innovations enable the optical surface of such mirrors to be rapidly tuned and stabilized on the nanometre scale within only a few seconds. [ABSTRACT FROM AUTHOR]

The tangential curvature of actively bent X‐ray mirrors at synchrotron radiation and X‐ray free‐electron laser (XFEL) facilities is typically only changed every few hours or even days. This operation can take tens of minutes for active optics with multiple bending actuators and often requires expert guidance using in situ monitoring devices. Hence, the dynamic performance of active X‐ray optics for synchrotron beamlines has historically not been exploited. This is in stark contrast to many other scientific fields. However, many areas of synchrotron radiation and XFEL science, including macromolecular crystallography, could greatly benefit from the ability to change the size and shape of the X‐ray beam rapidly and continuously. The advantages of this innovative approach are twofold: a large reduction in the dead time required to change the size of the X‐ray beam for different‐sized samples and the possibility of making multiple changes to the beam during the measurement of a single sample. In the preceding paper [Part I; Alcock, Nistea, Signorato & Sawhney (2019), J. Synchrotron Rad.26, 36–44], which accompanies this article, high‐speed visible‐light Fizeau interferometry was used to identify the factors which influence the dynamic bending behaviour of piezoelectric bimorph deformable X‐ray mirrors. Building upon this ex situ metrology study, provided here is the first synchrotron radiation beamline implementation of high‐speed adaptive X‐ray optics using two bimorphs operating as a Kirkpatrick–Baez pair. With optimized substrates, novel opto‐mechanical holders and a next‐generation high‐voltage power supply, the size of an X‐ray beam was rapidly and repeatedly switched in <10 s. Of equal importance, it is also shown that compensation of piezoelectric creep ensures that the X‐ray beam size remains stable for more than 1 h after making a major change. The era of high‐speed adaptive X‐ray optics for synchrotron radiation and XFEL beamlines has begun. Demonstrated here is the first simultaneous high‐speed beamline operation of a pair of piezoelectric bimorph deformable Kirkpatrick–Baez mirrors for the rapid and repeatable change and stabilization of the vertical and horizontal size of a synchrotron X‐ray beam within only a few seconds. This enables continuous adaptive shaping of the X‐ray beam in almost real time. Such innovations could lead to a major scientific change in how deformable X‐ray mirrors are used at synchrotron and X‐ray free‐electron laser sources. [ABSTRACT FROM AUTHOR]

Actively bent X-ray mirrors are important components of many synchrotron and X-ray free-electron laser beamlines. A high-quality optical surface and good bending performance are essential to ensure that the X-ray beam is accurately focused. Two elliptically bent X-ray mirror systems from FMB Oxford were characterized in the optical metrology laboratory at Diamond Light Source. A comparison of Diamond-NOM slope profilometry and finite-element analysis is presented to investigate how the 900 mm-long mirrors sag under gravity, and how this deformation can be adequately compensated using a single, spring-loaded compensator. It is shown that two independent mechanical actuators can accurately bend the trapezoidal substrates to a range of elliptical profiles. State-of-the-art residual slope errors of <200 nrad r.m.s. are achieved over the entire elliptical bending range. High levels of bending repeatability (Δ R/ R = 0.085% and 0.156% r.m.s. for the two bending directions) and stability over 24 h (Δ R/ R = 0.07% r.m.s.) provide reliable beamline performance. [ABSTRACT FROM AUTHOR]

Beam shaping is becoming increasingly important for synchrotron X-ray applications. Although routine for visible light lasers, this is challenging for X-rays due to the limited source coherence and extreme optical tolerances required for the shaping mirrors. In deliberate defocusing, even surface errors <5 nm r.m.s. introduce damagingly large striations into the reflected beam. To counteract such problems, surface modifications with alternating concave and convex curvature on equal segments were polished onto the surface of non-active mirrors of fixed curvature. Such optics are useful for providing a fixed size of X-ray beam, but do not provide the adaptability required by many experiments. In contrast, deformable piezo bimorph mirrors permit a continuous range of X-ray beam sizes and shapes. A new theory is developed for applying non-periodic modifications of alternating curvature to optical surfaces. The position and length of the segments may be freely chosen. For the first time, surface modifications of alternating curvature are applied to bimorph mirrors to generate non-Gaussian X-ray beam profiles of specified width. The new theory's freedom is exploited to choose the segments to match the polishing errors of medium wavelength (>10 mm) and the piezos' influence on the mirror's figure. Five- and seven-segment modifications of alternating curvature are calculated and verified by visible light and X-ray metrology. The latter yields beam profiles with less striation than those made by defocusing. Remaining beam striations are explained by applying geometrical optics to the deviations from the ideal surface modifications of alternating curvature. [ABSTRACT FROM AUTHOR]

The measurement of diffraction data from macromolecular crystal samples held in vacuo holds the promise of a very low X-ray background and zero absorption of incident and scattered beams, leading to better data and the potential for accessing very long X-ray wavelengths (>3 Å) for native sulfur phasing. Maintaining the hydration of protein crystals under vacuum is achieved by the use of liquid jets, as with serial data collection at free-electron lasers, or is side-stepped by cryocooling the samples, as implemented at new synchrotron beamlines. Graphene has been shown to protect crystals from dehydration by creating an extremely thin layer that is impermeable to any exchanges with the environment. Furthermore, owing to its hydrophobicity, most of the aqueous solution surrounding the crystal is excluded during sample preparation, thus eliminating most of the background caused by liquid. Here, it is shown that high-quality data can be recorded at room temperature from graphene-wrapped protein crystals in a rough vacuum. Furthermore, it was observed that graphene protects crystals exposed to different relative humidities and a chemically harsh environment. [ABSTRACT FROM AUTHOR]

Piezo bimorph mirrors are versatile active optics used on many synchrotron beamlines. However, many bimorphs suffer from the `junction effect': a periodic deformation of the optical surface which causes major aberrations to the reflected X-ray beam. This effect is linked to the construction of such mirrors, where piezo ceramics are glued directly below the thin optical substrate. In order to address this problem, a next-generation bimorph with piezos bonded to the side faces of a monolithic substrate was developed at Thales-SESO and optimized at Diamond Light Source. Using metrology feedback from the Diamond-NOM, the optical slope error was reduced to ∼0.5 µrad r.m.s. for a range of ellipses. To maximize usability, a novel holder was built to accommodate the substrate in any orientation. When replacing a first-generation bimorph on a synchrotron beamline, the new mirror significantly improved the size and shape of the reflected X-ray beam. Most importantly, there was no evidence of the junction effect even after eight months of continuous beamline usage. It is hoped that this new design will reinvigorate the use of active bimorph optics at synchrotron and free-electron laser facilities to manipulate and correct X-ray wavefronts. [ABSTRACT FROM AUTHOR]