Open Access

Show Abstract ▼

Abstract: The surface quality of x-ray mirrors is a major constraint on optical performance at synchrotron light and free electron laser facilities. A limiting factor for creating state-of-the-art optics is the accuracy of metrology data to deterministically guide the polishing tool to correct surface errors. The “MooNpics” (Metrology On One-Nanometer-Precise Optics) collaboration aims to improve optical metrology capabilities at European facilities to enable reproducible measurement of long or curved optics with height errors <1 nm rms and slope errors <100 nrad rms. Three challenging x-ray optics were measured by several labs using a variety of instruments. The mirrors, chosen to challenge and explore different aspects of optical metrology, were as follows: a 1 m-long, ultra-flat (radius of curvature R > 100 km); an ellipse with added parabolic arcs; and a strongly curved sphere (R ∼ 9.3 m) with an added spatially varying chirp. This study highlighted calibration issues with several instruments, which were subsequently corrected. In this paper, we present results about the ellipse mirror. Based on metrology data provided by the collaboration, two cycles of ion beam figuring improved all aspects of the mirror, including correcting the ellipse parameters, reducing high- and mid-frequency spatial polishing errors, and refining the shape of the parabolic arcs. Overall, the slope and height errors were improved by a factor of ∼10. We also show how the round-robin measurement exercise helped refine “best practice” procedures for mounting optics, alignment, and data acquisition and analysis methods. It is hoped that this collaborative project will ignite further improvements in the production quality of x-ray optics to benefit many scientific communities around the world.

Open Access

Show Abstract ▼

Abstract: Many optics at synchrotron and free electron laser facilities need to be cooled to dissipate the heat imparted by the intense photon beams. For indirectly cooled optics, distortion of the surface can occur when excessive or asymmetrical clamping forces are applied during assembly. To address this issue, it is necessary to monitor the effects of assembly and subsequent life cycle of the clamping forces applied to the crystal. We present experimental verification of a non-contact approach to the monitoring of clamping forces applied to the first crystal of a monochromator at Diamond Light Source using additively manufactured passive resonant structures. Laser vibrometery demonstrates the efficacy of this novel approach for assembly of indirectly cooled optics based on feedback from passive resonant structures. Fizeau interferometry of the optical surface reveals greater uniformity and repeatability when compared with a conventional approach to assembly. Furthermore, frequency shifts in the range of 20-60 Hz were observed in the passive structures after cryogenic cooling, indicative of a change in clamping force of up to approximately 25%.

Show Abstract ▼

Abstract: Key challenges for developing nanometrology are achieving high precision and accuracy under stringent environmental control to mitigate the impact of temperature, humidity, turbulence, and vibration. Additional complexities arise in accommodating the peculiarities of material behaviour at the nanoscale, in creating complex software to interpret large volumes of data efficiently, and in integrating various technologies within a single user-friendly instrument while managing costs and ensuring accessibility. This thesis presents advancements in X-ray optics nanometrology using speckle-based analysis on the basis of comprehensive exploration of the full range of innovative techniques for ex situ characterisation of X-ray optics. At the core of this research lies the intellectual challenge of obtaining successful characterisation of strongly curved X-ray mirror profiles (having radii of curvature smaller than 10m) in the form of 2D slope mapping data. The second challenge addressed in the thesis concerns providing the scientific community with an in-depth exploration and analysis of novel techniques and related metrology instrumentation. The thesis elaborates on the advancement of the mathematical models that underpin the new speckle-based metrology techniques. It also details the development of the requisite hardware and software tools. The research commences with an in-depth background study of synchrotron X-ray mirrors and the necessity for enhanced metrology to underpin further progress at large scale science facilities, such as synchrotron light sources. A thorough literature review is presented to evaluate the existing non-contact metrology methods, including Pencil Beam Interferometer, Long Trace Profiler, Nanometre Optical Metrology, Fizeau Interferometer, and Stitching Micro-Interferometer. The detailed study of the Speckle Angle Measurement (SAM) technique is presented. The methodology of SAM is expanded upon, including the experimental setup, data acquisition, precision, accuracy, calibration processes, and simulation. Critical analysis is presented of the principal factors influencing SAM, namely, the scanning head rotation and tilting angle of the Sample Under Test (SUT). The findings provide a solid demonstration of the effectiveness of SAM in the complete range of required capabilities, including the calibration, stability, simulation, and characterisation of various optics, including elliptical X-ray mirrors. The comparison between simulated and experimental results provides validation of the accuracy and applicability of SAM. The thesis concludes by highlighting the potential of SAM for applications such as Ion Beam Figuring at Diamond Light Source (DLS) and by highlighting further areas of research.

Open Access

Show Abstract ▼

Abstract: The Diamond-NOM slope profilometer has been in operation for more than 15 years in the Optics Metrology Lab at Diamond. It is an established instrument for accurate characterisation of x-ray optics for synchrotron and XFEL beamlines. However, continuous improvements in the fabrication quality of x-ray optics now means that polishing errors are comparable in magnitude to instrumental systematic errors. For x-ray optics with slope errors << 100 nrad rms and height errors < 1 nm, repeated measurements in multiple configurations are typically required to obtain accurate metrology data. To tackle such issues, we have developed a new instrument: the Diamond-VeNOM (velocity-NOM). VeNOM utilizes multiple autocollimators, synchronized with motion stages, to simultaneously measure the optical surface and monitor parasitic motion errors. A significant increase in measurement speed is achieved using 10x faster Elcomat5000 autocollimators. Motion trajectories are aligned with autocollimator data by temporarily blocking the beam paths using electronic shutters, based on triggering signals from positional encoders. Enhanced motion control capabilities allow user-defined velocity profiles of the scanning stage, coordinated with motorised pitch of the optic under test throughout the scan. This enables innovative dynamic scanning strategies, including on-the-fly, free-form, automated nulling of the optical surface throughout the scan to reduce systematic errors.

Open Access

Show Abstract ▼

Abstract: X-ray mirrors with single-digit nanometer height errors are required to preserve the quality of ultra-intense photon beams produced at synchrotron or free electron laser sources. To fabricate suitable X-ray mirrors, accurate metrology data is needed for deterministic polishing machines. Fizeau phase-shifting interferometers are optimized to achieve accurate results under nulled conditions. However, for curved or aspheric mirrors, a limited choice of reference optic often necessitates measurement under non-nulled conditions, which can introduce retrace error. Using experimental measurements of a multi-tilted calibration mirror, we have developed an empirical model of Fizeau retrace error, based on Zernike polynomial fitting. We demonstrate that the model is in good agreement with measurements of ultra-high quality, weakly-curved X-ray mirrors with sags of only a few tens of microns. Removing the predicted retrace error improves the measurement accuracy for full aperture, single shot, Fizeau interferometry to < 2 nm RMS.