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Abstract: Near-field X-ray speckle interferometry is a technique for X-ray multi-modal imaging that does not require optics and is very simple to implement. It is capable of producing absorption, phase, and scatter contrast images by utilizing random scattering media like sandpaper. The generation of these images relies on the correlation of near-field speckles, with one pattern recorded in the absence of an object and another with an object present. Our study focuses on comparing and evaluating various sub-sampling methods used in a correlation-based approach in real space. Additionally, we have analyzed the potential benefits and strengths of these sub-sampling methods in the context of X-ray speckle imaging using synchrotron radiation based X-ray source, and shown that cosine and Gaussian approximations provided superior sub-pixel delay estimations.

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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

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Abstract: Multilayer gratings are increasingly popular optical elements at X-ray beamlines, as they can provide much higher photon flux in the tender X-ray range compared with traditional single-layer coated gratings. While there are several proprietary software tools that provide the functionality to simulate the efficiencies of such gratings, until now the X-ray community has lacked an open-source alternative. Here MLgrating is presented, a program for simulating the efficiencies of both multilayer gratings and single-layer coated gratings for X-ray applications. MLgrating is benchmarked by comparing its output with that of other software tools and plans are discussed for how the program could be extended in the future.

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Abstract: Additive manufacturing (AM; 3D printing), which builds a structure layer-by-layer, has clear benefits in the production of lightweight mirrors for astronomy, as it can create optimised lightweight structures and combine multiple components into one. AM aluminium mirrors have been reported that demonstrate a 44% reduction in mass from an equivalent solid and the consolidation of nine parts into one. However, there is a limit on the micro-roughness that can be achieved using AM aluminium at ∼5nm RMS (root mean square; Sq), therefore, to target applications at shorter wavelengths alternative AM materials are required. New capabilities in AM ceramics, silicon carbide infiltrated with silicon (SiC + Si) and fused silica, offer the possibility to combine the design benefits of AM with a material suitable for visible, ultraviolet and x-ray applications. This paper will introduce the different printing methods and post-processing steps to convert AM ceramic samples into reflective mirrors. The samples are flat disks, 50mm diameter and 5mm in height, with three samples printed in SiC + Si and three printed in fused silica. Early results in polishing the SiC + Si material demonstrated that a micro-roughness of ∼2nm Sq could be achieved. To build on this study, the 50mm SiC + Si samples had three different AM finishing steps to explore the best approach for abrasive lapping and polishing, the reflective surfaces achieved demonstrated micro-roughness values varied between 2nm and 5nm Sq for the different AM finishing steps. To date, the printed fused silica material has heritage in lens applications; however, its suitability for mirror fabrication was to be determined. Abrasive lapping and polishing was used to process the fused silica to reflective surface and an average micro-roughness of <1nm Sq achieved on the samples.

Open Access

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Abstract: 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.