Optics
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Open Access
Abstract: As Diamond Light Source embraces the move towards becoming a fourth-generation light source its optics will be required to perform under increasingly demanding conditions. Foremost amongst these conditions will be the increasing power densities the optics are subjected to and the reducing real estate they have to perform in. With these new challenges comes the need for greater understanding of how optics are assembled and how consistently the activity is carried out. In this paper, the effect of bolt pretension during assembly of monochromators on distortion of the optical surface is investigated through numerical simulation. The results reveal skewed convex distortion of the optical surface in the meridional direction when uneven clamping force is applied, highlighting the importance of taking the potential for distortion of the optical surface due to clamping force into consideration.
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May 2022
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Metrology
Optics
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Open Access
Abstract: Reflective mirrors are used on most synchrotron and free electron laser (XFEL) beamlines to transport X-rays from the source to the sample. They are achromatic and provide larger acceptance and less absorption compared to compound refractive lenses. Mirrors whose surface profile can be controllably changed are called “active optics.” This enables users to vary the beam profile or focal position. X-ray beamlines use two categories of active optics: mechanically actuated mirrors, which typically use one or two independent bending motors for cylindrical or elliptical bending [1]; and piezoelectric bimorph deformable mirrors.
Bimorph deformable X-ray mirrors have been used to focus X-rays at synchrotron and XFEL beamlines since early research in the 1990s by Susini et al. [2] and Signorato et al. [3] at the European Synchrotron Radiation Facility (France). Soon afterwards, bimorph mirrors were commercialized by Thales-SESO (France) and deployed at several labs, including the Advanced Photon Source (USA) and Diamond Light Source (UK), called “Diamond” from here on. Research by Diamond’s Optics & Metrology (O&M) group shows that the widely held bad impression of bimorph mirrors as unreliable and excessively complex is outdated and unfounded. With fast, precise metrology techniques developed at Diamond, the difficulties encountered by the early users of bimorph mirrors have been overcome, and Diamond has combined bimorph actuators with specialized substrates for several novel applications. Finally, Diamond’s improvements can help realize the true potential of bimorph mirrors to act as closed-loop, adaptive X-ray optics with real-time correction. Such dynamic optics could match the profile of an X-ray beam to a series of rapidly changing samples of different shapes and sizes, or provide fast, stable wavefront correction.
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Apr 2022
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I16-Materials and Magnetism
Optics
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Open Access
Abstract: Crystal monochromators are often the primary optics in hard X-ray synchrotron beamlines. Management of power load is central to their design. Strict requirements on stability and deformation are to be met, as new-generation synchrotron sources deliver brighter beams of X-rays. This article sets out to illustrate an overall picture of the deformation caused by heat load in a cryo-cooled Si crystal monochromator using first principles. A theoretical model has been developed to predict the temperature distribution and surface deformation by applying intrinsic properties of Si material and the cooling system parameters. The model explains the universal behaviour of crystal slope error versus absorbed power; it has been benchmarked against experimental data and used to interpret finite-element analysis of cryogenically cooled crystals.
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Mar 2022
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Optics
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Open Access
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Feb 2022
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B16-Test Beamline
Optics
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Open Access
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Nov 2021
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Optics
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Open Access
Abstract: X-ray mirrors are widely used for synchrotron radiation, free-electron lasers, and astronomical telescopes. The short wavelength and grazing incidence impose strict limits on the permissible slope error. Advanced polishing techniques have already produced mirrors with slope errors below 50 nrad root mean square (rms), but existing metrology techniques struggle to measure them. Here, we describe a laser speckle angular measurement (SAM) approach to overcome such limitations. We also demonstrate that the angular precision of slope error measurements can be pushed down to 20nrad rms by utilizing an advanced sub-pixel tracking algorithm. Furthermore, SAM allows the measurement of mirrors in two dimensions with radii of curvature as low as a few hundred millimeters. Importantly, the instrument based on SAM is compact, low-cost, and easy to integrate with most other existing X-ray mirror metrology instruments, such as the long trace profiler (LTP) and nanometer optical metrology (NOM). The proposed nanometrology method represents an important milestone and potentially opens up new possibilities to develop next-generation super-polished X-ray mirrors, which will advance the development of X-ray nanoprobes, coherence preservation, and astronomical physics.
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Sep 2021
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Optics
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Open Access
Abstract: The formula relevant for linear optics design of synchrotrons are derived systematically from first principles, i.e., an exercise in Hamiltonian dynamics. Equipped with these, the relevant use cases are then captured; for a streamlined approach. To enable professionals, i.e., software engineers, to efficiently prototype & architect a CAD tool available to mechanical engineers since the mid-1960s. In other words, robust design of a modern synchrotron is an exercise in/pursuit of the art of Engineering-Science.
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Aug 2021
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B16-Test Beamline
Detectors
Optics
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Abstract: We performed simulations and experimental tests of a new method for improving the spatial resolution of x-ray imaging detectors using tilted angle irradiation. In this method, the x-ray beam arrives at the detector surface at an angle of <90° so that the beam footprint is expanded and the spatial resolution is increased. The proposed method is applicable for imaging with x-rays in the energy range of E = 0.2-15 keV, which is widely used for x-ray microscopy. The tilted angle irradiation technique can be applied to different types of x-ray microscopy detectors, including indirect conversion detectors (which consist of a scintillator optically coupled to the imaging camera), direct conversion detectors (such as CCD- and CMOS-based soft x-ray cameras) and some other semiconductor detectors. The experimental study described here employed an indirect detector configuration where a thin scintillator was optically coupled to an imaging camera via microscope optics. The spatial resolution was improved by a factor of 2.5 by using a tilt angle of 12° for 13.5 keV x-rays. This study will be continued using different xray energies and detector configurations.
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Aug 2021
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B16-Test Beamline
Optics
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Abstract: Thanks to the development of high-quality X-ray focusing optics during the past decades, synchrotron-based X-ray transmission microscopy techniques enable to study specimens with extremely high spatial resolution. However, on one hand at the expense of the field of view (100 μm x 100 μm) and on the other hand to the detriment of the photon energies range (below 20 keV), which significantly limits the specimens' scope to be investigated, particular- ly in material science.
In this work, the so-called pixel super-resolution scanning transmission hard X-ray microscopy technique was developed, allowing to enlarge the field of view and drastically reduce the scanning time thanks to sub-pixel specimen scanning through a large number of X-ray probes created by biconcave para- bolic shaped refractive multi-lenses. High-resolution images with a spatial resolution corresponding to the X-ray (micro-) nanoprobe size are achieved, even if the pixel size of an imaging detector employed for data acquisition is much larger than that.
Since the technique's key element is X-ray optics, the development and fabri- cation of one (two)-dimensional X-ray refractive multi-lenses (RMLs) for focusing high energy X-rays (17-35 keV) fabricated by deep X-ray lithogra- phy and electroplating technique are presented. The X-ray characterization of these optics and microscopy experiments performed at KARA (Germany), Diamond Light Source (England), and SPring-8 (Japan) synchrotron facilities are provided. Since the height of existing refractive multi-lenses still restricts the field of view (maximum in the mm range), the staircase array of RMLs inclined to the substrate was developed, allowing pixel super-resolution scanning transmission hard X-ray microscopy with a 1.64 cm × 1.64 cm field of view while keeping a 780 ± 40 nm resolution using 35 keV X-rays. The scanning time was only about four minutes. The unique capability of the pixel super-resolution scanning transmission hard X-ray microscopy has been demonstrated by imaging biomedical implant abutments fabricated via selective laser melting using Ti-6Al-4V. Accordingly, the investigation of extend- ed and thick specimens for material science has been demonstrated.
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Mar 2021
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B16-Test Beamline
Optics
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Abstract: Ptychography is a scanning coherent diffraction imaging technique that provides high-resolution imaging and complete spatial information of the complex probe and object transmission function. The wavefront error caused by aberrated optics has previously been recovered using ptychography when a highly coherent source is used, but has not been demonstrated with partial coherence due to the multi-modal probe required. Here, we demonstrate that partial coherence can be accounted for in ptychographic reconstructions using the multi-modal approach and assuming that decoherence arises from either the probe or the object. This equivalence recovers coherent (or single state) reconstructions of both the probe and the object even in the presence of partial coherence. We demonstrate this experimentally by using hard x-ray ptychography with a partially coherent source to image a Siemens star test object and to also recover the wavefront error from an aberrated beryllium compound refractive lens. The source properties and resolving capabilities are analyzed, and the wavefront error results are compared with another at-wavelength metrology technique. Our work demonstrates the capability of ptychography to provide high-resolution imaging and optics characterization even in the presence of partial coherence.
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Mar 2021
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