Here, we report the design, manufacturing, and characterization of x-ray optical components for the cavity-based x-ray free-electron laser (CBXFEL) cavity, in the framework of the CBXFEL R&D collaborative project of Argonne National Laboratory, SLAC National Accelerator Laboratory, and SPring-8. The optical components include high-reflectivity diamond crystal mirrors, reflecting and output coupling diamond drumhead crystal with thin membranes, focusing beryllium refractive lenses, and channel-cut Si crystal monochromators. All the designed optical components have been fully characterized at the Advanced Photon Source to demonstrate their desired performance for the CBXFEL cavity.
A coded-mask-based X-ray wavefront sensing technique was recently developed at the Advanced Photon Source, aiming for the ultimate phase sensitivity, spatial resolution and high speed using deep-learning-based analysis. It is a versatile tool capable of single-shot reference-free measurements and scanning mode for the best resolution and noise robustness. This work extends its application in at-wavelength metrology to achieve variable-resolution analysis when combined with a short-focal-length focusing optic. We showcase the complete characterization of beryllium refractive lenses using the coded-mask-based method in a collimated-beam setup and a divergent-beam setup with large geometric magnifications. The collimated-beam measurement provides the lens thickness error over the entire optical aperture down to a micron spatial resolution. On the other hand, wavefront sensing with the divergent beam can provide detailed local information of the sample with a few tens of nanometer spatial resolution, ideal for investigating lens defects.
The hard X-ray adaptive mirror optics will play an important role at next generation light sources. A dynamic mirror bender with capacitive sensor array as an in-situ mirror profiler is used for initial test for hard x-ray zoom optics has been designed and constructed. Previous work showcases the dynamic control of this elliptically bent hard X-ray mirror through applying a combination of neural networks algorithm and feedback control. In this paper, we present further control enhancement with machine learning techniques through optimization of the number and placement of the capacitive sensors and new sensor calibration with video-based coordinate measuring machine.
KEYWORDS: Mirrors, Hard x-rays, Machine learning, Control systems, Sensors, Profilometers, Feedback control, In situ metrology, Adaptive optics, Control systems design
This article showcases the high-resolution control of an elliptically bent hard X-ray mirror optics at the Advanced Photon Source. The mirror uses a compact laminar flexure bending mechanism to achieve elliptical shapes covering a large range of focal distances. An array of capacitive sensors are used as a surface profiler for in-situ monitoring of the mirror shape. Machine learning and control techniques were used to change the mirror shape and focus the incident X-ray at predefined focal planes. The mirror surface shape error can be controlled to be within 40 nm rms with high repeatability. This technique gives the capability to focus incident X-ray beam within a range of focal distances corresponding to shape deformation range of a mirror optics. This work would be beneficial for controlling similar adaptive optics for multiple adaptive optics systems.
The wavelet-transform-based single-shot X-ray speckle tracking (WXST) method combined with a multi-resolution analysis process was proposed to provide higher noise robustness and faster data processing compared with the correlation-based single-shot X-ray speckle tracking (CXST) technique. The new method was experimentally validated by measuring phase errors of beryllium compound refractive lenses in the transmission geometry. Taking advantages of the wavelet transform and the multi-resolution analysis, the data-analysis efficiency can be improved by two orders of magnitude for samples with phase variation over a large dynamical range. The multiresolution WXST method also shows high reconstruction accuracy and noise robustness. This novel method can broaden the potential applications of speckle-tracking techniques in wavefront sensing, at-wavelength metrology and phase imaging by breaking the bottleneck of the data processing.
Mirror-based zoom optics systems can offer variable focal spot sizes over a wide range, which is essential for coherent nanoprobe beamlines, such as the proposed Atomic beamline in the Advanced Photon Source (APS) upgrade project. The success of the zoom mirror system in the nano-focusing regime requires the development of high-precision deformable mirrors, in-situ surface profilers and wavefront sensors, and advanced feedback control system. A prototype 1-D zoom mirror system consists of two vertical focusing mirrors was designed, assembled, and tested at the APS 1-BM beamline. The system consists of a bender-based mirror with a capacitive-sensor- array-based real-time mirror profiler, a bimorph adaptive mirror, and a grating interferometer for the wavefront monitoring. In this work, we present the design and test results of the prototype system demonstrating its zoom focusing capability.
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