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167 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B16-Test Beamline Optics	Fast shaping control of X ray beams using a closed-loop adaptive bimorph deformable mirror Simon G. Alcock , Ioana-Theodora Nistea , Vivek G. Badami , Riccardo Signorato , Matteo Fusco , Lingfei Hu , Hongchang Wang , Kawal Sawhney Optica 10 DOI: 10.1364/OPTICA.476449 Open Access Show Abstract ▼ Abstract: High-speed adaptive correction of optics, based on real-time metrology feedback, has benefitted numerous scientific communities for several decades. However, it remains a major technological challenge to extend this concept into the hard x ray regime due to the necessity for active mirrors with single-digit nanometer height errors relative to a range of aspheric forms. We have developed a high-resolution, real-time, closed-loop “adaptive” optical system for synchrotron and x ray free electron laser (XFEL) applications. After calibration of the wavefront using x ray speckle scanning, the wavefront diagnostic was removed from the x ray beam path. Non-invasive control of the size and shape of the reflected x ray beam was then demonstrated by driving a piezoelectric deformable bimorph mirror at ∼1Hz . Continuous feedback was provided by a 20 kHz direct measurement of the optical surface with picometer sensitivity using an array of interferometric sensors. This enabled a non-specialist operator to reproduce a series of pre-defined x ray wavefronts, including focused or non-Gaussian profiles, such as flattop intensity or multiple split peaks with controllable separation and relative amplitude. Such changes can be applied in any order and in rapid succession without the need for invasive wavefront diagnostic sensors that block the x ray beam for scientific usage. These innovations have the potential to profoundly change how x ray focusing elements are utilized at synchrotron radiation and XFEL sources and provide unprecedented dynamic control of photon beams to aid scientific discoveries in a wide range of disciplines.	Jan 2023
Optics	An analytical approach to designing a future Nano-ARPES beamline for Diamond-II A. C. Walters , L. Alianelli , H. Wang , M. D. Watson , C. Cacho , C. Nicklin , K. Sawhney 14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021) DOI: 10.1088/1742-6596/2380/1/012039 Open Access Show Abstract ▼ Abstract: Angle-resolved photoemission spectroscopy (ARPES) is a powerful method for measuring the electronic band structure of solids. Diamond Light Source is planning to build a multibend-achromat (MBA) synchrotron – Diamond-II - which will provide an almost diffraction-limited photon source in the vacuum-ultraviolet photon energy range. The improved emittance and higher coherence of MBA synchrotrons means that samples with features smaller than 1 µm can be readily studied using ARPES, provided the beamline is designed to take full advantage of the new photon source. We have developed an analytical method for optimising the optical design of a future Nano-ARPES beamline for Diamond-II. Our method enables one to explore large regions of parameter space for a beamline design in an unbiased and systematic way, with minimal requirements on computing power. We believe that the analytical method presented here will be a useful tool for synchrotron beamline designers, as it allows many beamline characteristics to be simulated quickly while working within any practical limitations.	Dec 2022
Optics	Bimorph mirrors at synchrotron beamlines: from walking to flying John P. Sutter , Simon G. Alcock , Ioana-Theodora Nistea , Riccardo Signorato , Andrew Foster , Kawal Sawhney 14th International Conference on Synchrotron Radiation Instrumentation (SRI 2021) DOI: 10.1088/1742-6596/2380/1/012055 Show Abstract ▼ Abstract: With brighter synchrotron sources, automated sample changers, and faster detectors, there is a strong scientific need for rapid and precise variation of the X-ray beam profile, rather than the "set and forget" operation of years past. Piezoelectric bimorph deformable mirrors already allow quick beam profile changes without the heat generation and wear of mechanical devices. Now, their early technological limitations – excessively constraining holders, progressive "junction effect" distortion, and communication bottlenecks with power supplies – are being overcome by a collaboration of scientists and engineers both in industry and at Diamond Light Source. A new generation of bimorph mirrors maintains a stable figure over extended periods of operation. Improved holders and flexible electrical connectors are greatly reducing the mechanical strain imparted to bimorphs, thereby improving their speed, accuracy, and stability. A more sophisticated high voltage power supply has on-board signal processing capacity, allowing large focusing changes within seconds and providing programmable time-varying voltage profiles to counteract piezoelectric creep. The communication between beamline systems and power supplies is being freed of bottlenecks and now runs stably up to 1 Hz. Early tests have already shown that bimorph mirrors can repeatedly switch the size of an X-ray beam in well under 10 seconds. Bimorph mirrors at synchrotron beamlines are now growing beyond the largely static operation of the past and gaining a new dynamism through development projects that are now well advanced. We report on how these endeavours will make it easier for beamlines to utilise the full potential of bimorph mirrors.	Dec 2022
Optics	A Fizeau interferometry stitching system to characterize X-ray mirrors with sub-nanometre errors Murilo B. Da Silva , Simon G. Alcock , Ioana-Theodora Nistea , Kawal Sawhney Optics And Lasers In Engineering 161 DOI: 10.1016/j.optlaseng.2022.107192 Open Access Show Abstract ▼ Abstract: We present the development of a Fizeau interferometer stitching system to characterize the surface profile of state-of-the-art X-ray optics for synchrotron and free electron laser sources. Controls and acquisition software precisely translate and rotate the surface under test in synchrony with data capture by a Zygo Verifire HDX interferometer. Overlapping sub-aperture images are combined into a composite, high-spatial resolution topographical image of the entire optical surface using PyLOSt stitching software produced by the MooNpics collaboration. After minimization of random and systematic measurement errors, system performance was quantified by characterizing two challenging optics. These optics represent extreme cases for synchrotron X-ray mirrors: an aspheric elliptical profile with a slope error of ∼50 nrad rms, and a corresponding height error of 0.2 nm rms; and a chirped periodic structure superimposed upon a strong curvature (radius ∼ 9.33 m). Results are in very good agreement with the Diamond-NOM slope profilometer and Bruker GTX stitching micro-interferometer. Without a specialist transmission reference, both optics could not be measured by the interferometer without pitch and translation stitching. Any individual HDX scan, relative to the average of the ensemble, has an average slope error repeatability of < 15 nrad rms. After calibration of the transmission reference flat and zoom factor, a reproducibility of ∼ 27 nrad rms compared to the Diamond-NOM, was achieved for the elliptically curved mirror.	Nov 2022
B16-Test Beamline Metrology Optics	Two-dimensional speckle technique for slope error measurements of weakly focusing reflective X-ray optics Lingfei Hu , Hongchang Wang , Oliver Fox , Kawal Sawhney Journal Of Synchrotron Radiation 29 DOI: 10.1107/S160057752200916X Open Access Show Abstract ▼ Abstract: Speckle-based at-wavelength metrology techniques now play an important role in X-ray wavefront measurements. However, for reflective X-ray optics, the majority of existing speckle-based methods fail to provide reliable 2D information about the optical surface being characterized. Compared with the 1D information typically output from speckled-based methods, a 2D map is more informative for understanding the overall quality of the optic being tested. In this paper, we propose a method for in situ 2D absolute metrology of weakly focusing X-ray mirrors. Importantly, the angular misalignment of the mirror can be easily corrected with the proposed 2D processing procedure. We hope the speckle pattern data processing method presented here will help to extend this technique to wider applications in the synchrotron radiation and X-ray free-electron laser communities.	Nov 2022
B16-Test Beamline Optics	Fast wavefront sensing for X-ray optics with an alternating speckle tracking technique Lingfei Hu , Hongchang Wang , Oliver Fox , Kawal Sawhney Optics Express 30 DOI: 10.1364/OE.460163 Open Access Show Abstract ▼ Abstract: Advances in accelerator technologies have enabled the continuous development of synchrotron radiation and X-ray free electron laser (XFEL) sources. At the same time, it has been critical to perform in-situ wavefront sensing to aid delivery of high-quality X-ray beams to the end users of these facilities. The speckle-based scanning technique has obtained popularity due to its high spatial resolution and superior sensitivity compared to other wavefront sensing methods. However, these advantages often come at the expense of longer data acquisition times since multiple images have to be collected to derive the necessary wavefront information. Whereas initial speckle tracking techniques could obtain wavefront information relatively quickly, the installation of additional hardware was routinely required to do so. Here, we propose a novel speckle-based approach, termed Alternating Speckle Tracking (AST), to perform fast wavefront sensing within a conventional beamline setup. The wavefront information derived from the new technique has proven to be valuable for many applications that require temporal resolution. Importantly, both horizontal and vertical wavefront information can be simultaneously derived by moving the speckle generator along the diagonal direction. We expect this method will be widely used by the synchrotron radiation and XFEL community in the future.	Aug 2022
B16-Test Beamline Optics	Two-dimensional wavefront characterization of adaptable corrective optics and Kirkpatrick–Baez mirror system using ptychography Thomas E. J. Moxham , Vishal Dhamgaye , David Laundy , Oliver J. L. Fox , Hossein Khosroabadi , Kawal Sawhney , Alexander Korsunsky Optics Express 30 DOI: 10.1364/OE.453239 Open Access Show Abstract ▼ Abstract: Aberrations introduced during fabrication degrade the performance of X-ray optics and their ability to achieve diffraction limited focusing. Corrective optics can counteract these errors by introducing wavefront perturbations prior to the optic which cancel out the distortions. Here we demonstrate two-dimensional wavefront correction of an aberrated Kirkpatrick-Baez mirror pair using adaptable refractive structures. The resulting two-dimensional wavefront is measured using hard X-ray ptychography to recover the complex probe wavefield with high spatial resolution and model the optical performance under coherent conditions. The optical performance including the beam caustic, focal profile and wavefront error is examined before and after correction with both mirrors found to be diffraction limited after correcting. The results will be applicable to a wide variety of high numerical aperture X-ray optics aiming to achieve diffraction limited focussing using low emittance sources.	May 2022
Metrology Optics	Active and adaptive X-ray optics at Diamond Light Source John P. Sutter , Simon G. Alcock , Ioana-Theodora Nistea , Hongchang Wang , Kawal Sawhney Synchrotron Radiation News 24, 1 - 6 DOI: 10.1080/08940886.2022.2058856 Open Access Show Abstract ▼ 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.	Apr 2022
I16-Materials and Magnetism Optics	Cryo-cooled silicon crystal monochromators: a study of power load, temperature and deformation Hossein Khosroabadi , Lucia Alianelli , Daniel G. Porter , Steve Collins , Kawal Sawhney Journal Of Synchrotron Radiation 29 DOI: 10.1107/S160057752200039X Open Access Show Abstract ▼ 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.	Mar 2022
Optics	Refractive optics for modifying X-ray wavefronts David Laundy , Thomas Moxham , Vishal Dhamgaye , Hossein Khosroabadi , Oliver Fox , Kawal Sawhney Synchrotron Radiation News DOI: 10.1080/08940886.2021.2022400 Open Access	Feb 2022

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