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Abstract: A new class of 3rd generation, bimorph deformable, X-ray mirrors have been developed, which are UHV “bakeable” to 200°C and provide diffraction-limited performance for achromatic focusing and wavefront correction of high-intensity photon beams. Optical metrology was used to reduce slope errors to ∼ 42 nrad rms and height errors to ∼ 200 pm rms for concave, flat, and convex elliptical curvatures. Curved X-ray mirrors with slope errors < 50 nrad rms and height errors < 500 pm rms are required for nano-focusing and coherence applications at low-emittance synchrotron light and free electron laser facilities. In recent years, impressive technical progress has been made to fabricate fixed-curvature X-ray mirrors, approaching diffraction-limited performance. However, for many scientific applications, active optics with a deformable surface profile are required to intermittently change the focal distance or size of the X-ray beam, or to make fine adjustments to the X-ray wavefront. What we believe to be a new class of high-grade, actively deformable optics have been developed, which provide diffraction-limited performance for achromatic focusing and wavefront correction of X-ray beams. 3rd generation, bimorph deformable, X-ray mirrors have piezoelectric PZT actuators bonded to the silicon substrate using silver nano-particles. They can be safely thermally annealed to 200°C and are ultra-high vacuum compatible, making them suitable for a wide range of X-ray energies, including soft X-rays. We present a comprehensive optical metrology study of a 32-channel, 3rd generation bimorph mirror mounted in an opto-mechanical holder to assess suitability for routine beamline operation. Fizeau interferometry and slope profilometry were performed to characterize the range, drift, stability, repeatability, and resolution of bending. Voltages to individual electrodes were optimized to minimise surface errors, based on metrology feedback and a constrained, linear algebra solver. Slope errors of ∼ 42 nrad rms and height errors ∼ 200 pm rms were achieved for three different curvatures (concave, flat, and convex). Metrology testing also demonstrated the extreme resolution of bending (2 nm changes in the height profile by incrementally applying 0.1 V shifts to all piezo actuators) and long-term curvature stability of 0.1% rms over 16 hours. Hysteresis, creep, and short-term drift of the bimorph’s profile were observed, which will be the subject of future research.

Open Access

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Abstract: Customized beam shaping has a wide range of applications from visible light to hard X-rays. While laser beam shaping has matured over recent decades, enabling breakthroughs in optical communication, optical tweezers, and advanced microscopy, extending these techniques to high-brightness X-ray sources could significantly enhance synchrotron applications such as macromolecular crystallography, spectroscopy, and high-resolution imaging. However, X-ray beam shaping remains challenging due to limitations in the available optics and the finite phase-space of synchrotron sources. We introduce a novel method that exploits the monochromatic angular spectrum of undulator radiation combined with the compound refractive lenses (CRLs) to produce a variable circular focal spot with a top-hat intensity profile. By fine-tuning the undulator gap and monochromator settings, this approach enables dynamic control of the spatial beam profile while preserving continuous energy tunability within the limits imposed by the optical configuration and experimental conditions. This technique delivers flexible beam shaping without requiring complex new optical designs, construction, or operational overhead. This method has been successfully demonstrated on a macromolecular crystallography beamline at the Diamond Light Source (DLS), confirming its practicality, adaptability, and potential for widespread adoption in synchrotron-based research.

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Abstract: The internal layer structure and optical performance of coating for X-ray free-electron laser (XFEL) applications were studied. Surface morphology analysis shows that the layer growth at 5 mTorr replicates the substrate morphology at low and mid frequencies but adds slight high-frequency roughness, with the RMS value increasing from 0.13 to 0.33 nm. To investigate the internal physical and chemical structure of , angle-resolved X-ray photoelectron spectroscopy (ARXPS) and depth profiling were performed. Together with soft X-ray (SXR) and hard X-ray (HXR) reflectivity measurements and the fitted results, a three-sublayer model with different composition and density was built for the 50 nm coating. The developed coating was further deposited on a 600 mm length mirror with a thickness variation of 0.7 nm (peak-to-valley). The radius of curvature changed slightly from 181 km before coating to 128 km after coating, and the slope errors were maintained at around 0.07 µrad, indicating a high-performance and large-size coating for the XFEL.

Open Access

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Abstract: High-performance synchrotron X-ray focusing mirrors require aspheric surfaces with nanoradian slope accuracy, which are challenging to provide for many manufacturers. Conventional grinding and polishing techniques typically introduce tooling marks to the surface during the fabrication process, and these marks can impose significant challenges for the deterministic figuring processes used as the final step in mirror fabrication, ultimately limiting the slope errors of the mirrors. To overcome this limitation, we present an alternative approach by using ion beam shaping to form an elliptical sub-microfocusing mirror from a flat mirror, followed by ion beam figuring to improve the remaining errors. Two mirrors fabricated using this approach achieved tangential slope errors below 200 nrad root mean squared (rms), in contrast to a conventionally pre-shaped mirror with identical ellipse parameters that was limited to > 500 nrad rms after ion beam figuring due to residual tooling marks. In X-ray focusing tests, the ion beam shaped mirrors are able to realise a spot size below 250 nm (full width half maximum), compared to 404 nm for the pre-shaped mirror. This demonstrates the excellent potential of ion beam shaping as a method for rapid, efficient and high-quality X-ray mirror fabrication.

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Abstract: Autocollimators are used in profilometers for the precise form measurement of beam-shaping optics for synchrotron light sources and x-ray free-electron lasers. This application requires using an aperture stop, typically 2.5 mm in diameter, which limits the footprint of the autocollimator’s measuring beam on the optics to achieve a sufficiently high lateral resolution. Central to the development of profilometry has been the availability of commercial autocollimators, such as the Elcomat 3000 from Möller–Wedel Optical. Although autocollimators are generally not designed for use with small apertures, this device has proven capable and has become the de facto standard. Now that it has been replaced by the Elcomat 5000, we evaluate the performance of several autocollimators of this type at small apertures, including the characterization of instrument transfer functions with a chirped height profile. We demonstrate that the Elcomat 5000 is capable of repeatable angle measurements with a standard deviation of 0.014 arcsec at an aperture diameter of 1.6 mm, whereas the Elcomat 3000 achieves 0.03 arcsec at 2.5 mm, comparing models with modified reticle designs. We also investigate the influence of optical aberrations of the autocollimator’s objective and their changes with the path length to the surface under test. We characterize the sensitivity of the angle measurement to changes in environmental parameters, in particular, barometric pressure. These efforts are aimed at approaching fundamental limits in the characterization of the shape of optical surfaces with autocollimator-based profilometers so that these are ready for characterizing the next generation of synchrotron and XFEL beamline optics.