This PDF file contains the front matter associated with SPIE Proceedings Volume 12697, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

FOCUS (Fast Monte CarlO approach to Coherence of Undulator Sources) is a new GPU-based code to compute the transverse coherence of x-ray radiation from undulator sources. It combines analytic descriptions of the emitted electric fields with massively parallel computation on GPUs, thereby reducing computation times by up to five orders of magnitude with respect to standard codes. Here we report on recent developments of FOCUS, including new functionalities and some performance optimizations. We also show results for current third-generation facilities and more modern, low-emittance x-ray sources close to the diffraction limit. Finally, we discuss future upgrades and highlight possible perspectives.

A wavefront split propagator dedicated to the simulation of wavefront propagation through high-resolution x-ray nano-focusing optics system has been implemented in Synchrotron Radiation Workshop (SRW). The new propagator integrated the Shifted Angular Spectrum (Shift-AS) method and the sub-wavefront approach with SRW's original transmission optics and standard drift-space propagators. This approach allowed for a significant reduction of memory required for the simulation of wavefront propagation through Fresnel zone plates with very large numbers of zones and other high-resolution focusing optics while preserving the accuracy of the numerical wave-optics calculation. We introduce the two approaches, i.e., the sub-wavefront approach and Shift-AS approach, and describe their implementation and program structure in the new SRW’s wavefront split propagator. Using the potential Fresnel zone plates of Soft X-ray Nanoprobe (SXN) beamline at NSLS-II as examples, we demonstrate this new propagator, and report on its high accuracy and memory-saving capabilities by comparing the calculation result with those by the original propagators, and also point to future applications of this approach.

We compare the general Coherent Mode Decomposition (CMD) method implemented in SRW code and the method making use of Hermite-Gaussian functions implemented in SPECTRA code, both methods being applied to partially coherent Undulator Radiation (UR). The comparison is made in terms of modes required for the same accuracy of presentation of 4D cross spectral density and Wigner function of UR for the same electron beam and undulator systems (corresponding to modern high-brightness light sources – currently operating NSLS-II and the planned upgrade of SPring-8). We show that, even though the pre-defined orthogonal analytical functions are not the exact eigenmodes of the partially coherent UR, their use can be perfectly justified in many cases for the UR, especially when limited computational resources are available for performing the numerical decomposition. Before analyzing the CMD results, we also illustrate excellent agreement between UR characteristics computed with SPECTRA and with SRW. All the presented comparisons, and the agreements found, confirm the validity of methods used by the codes and accuracy of their results.

We have used coherent wavefront propagation simulation (in python) to demonstrate that the current generation of bimorph deformable mirrors can be used as a pre-mirror in a grating monochromator to improve their performance and expand their range of application. We have used influence functions acquired from an existing deformable mirror to make sure the wavefront correction can be achieved in actual implementations and establish a set of specification requirements for such mirrors (number of actuators, precision, distance between the optical elements.) We also discuss the relative benefits of positioning the adaptive mirror before or after the grating, and we show that given typical beamline designs and undulator bandwidth, such a solution is viable to achieve wavefront correction on a dispersed beam and achieve photon energy high resolution to go beyond the limitations of state-of-the-art manufacturing capabilities of gratings.

The hard x-ray instruments at the Linac Coherent Light Source are in the design phase for upgrades that will take full advantage of the high repetition rates that will become available with LCLS-II-HE. The current x-ray correlation spectroscopy instrument will be converted to the dynamic x-ray scattering instrument and will feature a meV-scale high-resolution monochromator at its front end with unprecedented coherent flux. With the new capability come many engineering and design challenges, not least of which is the sensitivity to long-term drift of the optics. With this in mind, we have estimated the system tolerance to angular drift and vibration for all the relevant optics (approximately ten components) in terms of how the central energy out of the monochromator will be affected to inform the mechanical design. Additionally, we have started planning for methods to correct for such drifts using available (both invasive and non-invasive) x-ray beam diagnostics. In simulations, we have demonstrated the ability of trained Machine Learning models to correct misalignments to maintain the desired central energy and optical axis within the necessary tolerances. Additionally, we exhibit the use of Bayesian Optimization to minimize the impact of thermal deformations of crystals as well as beam alignment from scratch. The initial results are very promising and efforts to further extend this work are ongoing.

The idea of start-to-end simulation for experiments at advanced light sources, such as x-ray free-electron laser facilities and synchrotron facilities, has been proposed for several years. Such a simulation workflow aims to enable the tracking of x-ray radiation from its source, through the beam transportation to the photon-matter interaction region, and finally, to a photon detector. Several extant software programs simulating different aspects of an experiment have been assembled into the SIMEX platform, which has enabled several insightful works on single-particle imaging. However, the platform’s complicated and sometimes conflicting dependencies have hindered its adoption in other fields, and the scientifically intrinsic complication of each part of the workflow made it challenging for users to optimize all necessary parameters. To address these challenges, we have developed SimEx-Lite, a new core python interface in the SIMEX platform that utilizes optimized templates, personalized back engine installation, new data and parameter classes based on libpyvinyl. This paper introduces the architecture of SimEx-Lite and illustrates its applicability and usefulness in scientific research through selected examples at XFEL facilities.

In this contribution we discuss two major classes of transversely partially coherent x-ray sources: undulators in storage rings and SASE free-electron lasers. We address similarities and differences in terms of statistical and coherence properties, highlighting their relation with state-of-the-art numerical methods used to simulate the emitted wavefronts and their propagation down a beamline. We also report on recent developments based on simplifying analytical approximations and the use of physical models, leading to fast techniques with improved numerical efficiency particularly suitable for realistic description of spontaneous emission in undulator sources.

Detailed physical optics simulations of beamlines and experiments offer great value towards efficiently utilizing light source facilities. They make it possible to study their predicted behaviors under configurations which can be controlled more precisely than in physical experiments. Synchrotron Radiation Workshop (SRW) is a state-of-the-art software package for such simulations. Through its Python-based interface and browser-based interface Sirepo, SRW supports the definition of detailed optical schemes with many types of optical elements, and the simulation of radiation propagation through them. SRW has been mainly focused on CPU-based calculations; however, due to many of the operations being embarrassingly parallel, there is significant potential for accelerating these calculations using general-purpose GPU computation. In this work, the application of GPU accelerated computing to SRW for accelerating time-dependent coherent x-ray scattering experiments is discussed. A detailed simulation of a typical X-ray Photon Correlation Spectroscopy experiment for characterizing the dynamics of a colloidal sample was performed. Large improvements in simulation speed were demonstrated by converting the radiation propagation operations for the associated optical elements to use GPU computation. Combined with coherent mode decomposition, this resulted in a qualitative leap forward in the calculation speed and level of detail at which similar partially coherent scattering experiments can be simulated. These improvements have wide-ranging applications, such as assisting in the development of improved data processing methods and allowing for more detailed analysis of proposed experiments before using beam time.

Near-perfect diffracting crystals have many uses in x-ray optics including as monochromators, energy analyzers, and phase retarders. The usefulness of a particular Bragg reflection is often related to its angular acceptance and efficiency, as is determined by the reflection’s structure factor. Silicon crystals, which belong to the same face-centered cubic space group 𝐹𝑑3̅𝑚 as germanium and diamond, are readily available in large and highly pure ingots. Combined with their high thermal conductivity and low thermal expansion, this makes them suitable for synchrotron x-ray beamlines. However, less symmetric trigonal crystals such as sapphire, lithium niobate, and α-quartz offer a better choice of high-energy-resolution Bragg reflections near backscattering with less likelihood of parasitic Bragg reflections. Because these crystals’ atoms vibrate anisotropically and shift relative to each other with temperature, the temperature dependence of their structure factors is not a given by a simple Debye-Waller factor. Also, many crystal structures may be described by several different conventions of origin and lattice vectors. A Python three software package, PyCSFex, is presented here for the rapid calculation of large numbers of structure factors of any crystal described in any convention. It can run on its own or as part of an already existing software package. Users can extend the package to new crystals by writing their own material files. α-Quartz is chosen as an example because it has already been successfully used in backscattering x-ray energy analyzers and presents the complexities previously mentioned.

The autonomous alignment of synchrotron beamlines is typically a high-dimensional, high-overhead optimization problem, requiring us to predict a fitness function in many dimensions using relatively few data points. A model that performs well under these conditions is a Gaussian process, upon which we can apply the framework of classical Bayesian optimization methods. We show that even with no prior data, a tailored Bayesian optimization algorithm is capable of autonomously aligning up to eight dimensions of a digital twin of the TES beamline at NSLS-II in only a few minutes. We implement this approach in a software package for automatic beamline alignment, which is available out-of-the-box for any facility that leverages the Bluesky environment for beamline manipulation and data acquisition.

In experiments utilizing fourth-generation synchrotron radiation and Free Electron Laser (FEL) beamlines, a primary challenge for X-ray optical elements is to achieve and maintain high-intensity focused x-ray beams with near-perfect wavefront quality and high stability. These optical elements inherently demand more stringent specifications than those for other applications because of the shorter wavelength and the ultra-small emittance of the radiation beams from these sources. Coherent photons from diffraction-limited light sources further underscore the necessity for a controlled wavefront. Maintaining a uniform wavefront is crucial for phase-sensitive imaging techniques and for various coherent x-ray scattering experiments, such as tomography, coherent x-ray diffraction imaging, x-ray photon correlation spectroscopy and coherent surface scattering imaging. Therefore, x-ray optics must be manufactured close to ideal mathematical shapes, automatically align and focus beams according to experimental needs, and offer real-time correction to wavefront deformations. At the Advanced Photon Source (APS), we have demonstrated the application of a neural network model to automatically control deformable mirrors and the use of Bayesian optimization with Gaussian processes to align and stabilize focusing optical systems.

The Sirepo-Bluesky library allows the performing of various types of Bluesky scans with Sirepo simulations acting as virtual beamlines and registration of the results with the Databroker library. We report on the progress made since the previous SPIE’2020. In particular, the support for Shadow3 and MAD-X simulation codes in Sirepo was added to the Sirepo-Bluesky library, and the API for the support of the Sirepo/SRW code was refactored. Significant efforts were put into reliable testing and documentation. A “digital twin” of the future NSLS-II ARI beamline was created and the future Bluesky scans were prototyped using the Sirepo/SRW simulations. This approach enables new optimization methods for automated instrument alignment based on the Ophyd/Bluesky and makes them transferable from simulated to various hardware backends.