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- Front Matter: Volume 9209
- Fundamentals and Facility Reports I
- Fundamentals and Facility Reports II
- Methods and Codes I
- Methods and Codes II
- Instruments and Beamlines
- Crystal Optics
- High-Resolution Focusing Optics and Imaging I
- High-Resolution Focusing Optics and Imaging II
- Poster Session
Front Matter: Volume 9209
Front Matter: Volume 9209
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 9209 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Fundamentals and Facility Reports I
Partial coherence and imperfect optics at a synchrotron radiation source modeled by wavefront propagation
Show abstract
A full wave propagation of X-rays from source to sample at a storage ring beamline requires simulation of the electron beam source and optical elements in the beamline. The finite emittance source causes the appearance of partial coherence in the wave field. Consequently, the wavefront cannot be treated exactly with fully coherent wave propagation or fully incoherent ray tracing. We have used the wavefront code Synchrotron Radiation Workshop (SRW) to perform partially coherent wavefront propagation using a parallel computing cluster at the Diamond Light Source. Measured mirror profiles have been used to correct the wavefront for surface errors.
Simulations applied to focusing optics at European XFEL
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European X-ray Free Electron Laser (XFEL) in Hamburg will be most powerful FEL source in the world. It will deliver
coherent X-ray pulses with femtosecond duration and high repetition rate up to 4.5 MHz. For beam conditioning all the
end stations at European XFEL will be using focusing optics, the grazing incidence KB mirrors or/and Compound
Refraction Lenses (CRLs). For precise design and specification of optical components, one faces problems that require
full-scale wavefront simulations, taking into account optics imperfections and diffraction effects on apertures. We
present application examples of wavefront simulations for various focusing optics schemes at the European XFEL, such
as extreme focusing with long KB mirrors, concurrent impact of diffraction on the apertures of the mirrors cutting the
beam and quality of the mirror surfaces. status of software framework for start to end simulation for single particle
imaging experiments is also described.
Simulations of x-ray optics for ESRF-upgrade programme
Show abstract
The ESRF Upgrade includes construction of long beamlines to use routinely nano-beams. This requires a very high
demagnification of the ESRF source, which makes beamline optics design a fundamental concept for the future
availability of bright and small stable beam. A summary of recent simulations for Upgrade beamlines is presented,
including transfocators, bent crystals and graded multilayers. Some examples of particular calculations are described. In
parallel to the Upgrade Programme, an ambitious project for the upgrade and integration of existing software and
development of new toolbox is been carried out, with particular interest in beam polarization and partial coherence.
Fundamentals and Facility Reports II
Recent updates in the “Synchrotron Radiation Workshop” code, on-going developments, simulation activities, and plans for the future
Show abstract
Recent updates in the “Synchrotron Radiation Workshop” physical optics computer code, including the transition to the
Open Source development format, the results of the on-going collaborative development efforts in the area of X-ray
optics, in particular grazing incidence mirrors, gratings and crystal monochromators, and in other areas, as well as some
simulation activities for storage ring and X-ray free-electron laser sources are reported. Future development plans are
discussed.
Methods and Codes I
Propagation of coherent light pulses with PHASE
Show abstract
The current status of the software package PHASE for the propagation of coherent light pulses along a synchrotron
radiation beamline is presented. PHASE is based on an asymptotic expansion of the Fresnel-Kirchhoff integral
(stationary phase approximation) which is usually truncated at the 2nd order. The limits of this approximation as well as
possible extensions to higher orders are discussed. The accuracy is benchmarked against a direct integration of the
Fresnel-Kirchhoff integral. Long range slope errors of optical elements can be included by means of 8th order
polynomials in the optical element coordinates w and l. Only recently, a method for the description of short range slope
errors has been implemented. The accuracy of this method is evaluated and examples for realistic slope errors are given.
PHASE can be run either from a built-in graphical user interface or from any script language. The latter method provides
substantial flexibility. Optical elements including apertures can be combined. Complete wave packages can be
propagated, as well. Fourier propagators are included in the package, thus, the user may choose between a variety of
propagators. Several means to speed up the computation time were tested - among them are the parallelization in a multi
core environment and the parallelization on a cluster.
X-ray optics simulation and beamline design using a hybrid method: diffraction-limited focusing mirrors
Show abstract
A hybrid method combining ray-tracing and wavefront propagation was recently developed for X-ray optics
simulation and beamline design optimization. One major application of the hybrid method is its ability to assess
the effects of figure errors on the performance of focusing mirrors. In the present work, focusing profiles of
mirrors with different figure errors are simulated using three available wave optics methods: the hybrid code
based on the Fourier optics approach, the stationary phase approximation and a technique based on the direct
Fresnel-Kirchhoff diffraction integral. The advantages and limitations of each wave optics method are discussed.
We also present simulations performed using the figure errors of an elliptical cylinder mirror measured at APS
using microstitching interferometry. These results show that the hybrid method provides accurate and quick
evaluation of the expected mirror performance making it a useful tool for designing diffraction-limited focusing
beamlines.
Methods and Codes II
Powerful scriptable ray tracing package xrt
Show abstract
We present an open source python based ray tracing tool that offers several useful features in graphical presentation,
material properties, advanced calculations of synchrotron sources, implementation of diffractive and refractive elements,
complex (also closed) surfaces and multiprocessing. The package has many usage examples which are supplied together
with the code and visualized on its web page.
We exemplify the present version by modeling (i) a curved crystal analyzer, (ii) a quarter wave plate, (iii) Bragg-Fresnel
optics and (iv) multiple reflective and non-sequential optics (polycapillary). The present version implements the use of
OpenCL framework that executes calculations on both CPUs and GPUs. Currently, the calculations of an undulator
source on a GPU show a gain of about two orders of magnitude in computing time.
The development version is successful in modelling the wavefront propagation. Two examples of diffraction on a plane
mirror and a plane blazed grating are given for a beam with a finite energy band.
Novel applications of the x-ray tracing software package McXtrace
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We will present examples of applying the X-ray tracing software package McXtrace to different kinds of X-ray
scattering experiments. In particular we will be focusing on time-resolved type experiments. Simulations of full
scale experiments are particularly useful for this kind, especially when they are performed at an FEL-facility.
Beamtime here is extremely scarce and the delay between experiment and publication is notoriously long. A
major cause for the delay is the general complexity of the experiments performed. A complexity which arises
from the pulsed state of the source.
As an example, consider a pump-and-probe type experiment. In order to get the wanted signal from the
sample the X-ray pulse from the FEL source needs to overlap in space and time with the pumping pulse inside the
sample. This is made more difficult by several effects: The sample response may be dependent of the polarisation
of the pumping and/or probing pulse. There may be significant time-jitter in the pulse arrival times. The
composition of the sample may vary depending on local sample geometry and be modified by the probing pulse.
Many of the samples considered are in a liquid state and thus have a variable geometry. ...to name some of the
issues encountered. Generally more than one or all of these effects are present at once.
Simulations can in these cases be used to identify distinct footprints of such distortions and thus give the
experimenter a means of deconvoluting them from the signal.
We will present a study of this kind along with the newest developments of the McXtrace software package.
MASH: a framework for the automation of x-ray optical simulations
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MASH stands for Macros for the Automation of SHadow". It allows to run a set of ray-tracing simulations,
for a range of photon energies for example, fully automatically. Undulator gaps, crystal angles etc. are tuned automatically. Important output parameters, such as photon flux, photon irradiance, focal spot size, bandwidth, etc. are then directly provided as function of photon energy. A photon energy scan is probably the most commonly requested one, but any parameter or set of parameters can be scanned through as well.
Heat load calculations with finite element analysis providing temperatures, stress and deformations (Comsol) are fully integrated. The deformations can be fed back into the ray-tracing process simply by activating a switch.
MASH tries to hide program internals such as le names, calls to pre-processors etc., so that the user (nearly) only needs to provide the optical setup.
It comes with a web interface, which allows to run it remotely on a central computation server. Hence, no local installation or licenses are required, just a web browser and access to the local network.
Numerous tools are provided to look at the ray-tracing results in the web-browser. The results can be also downloaded for local analysis. All files are human readable text files that can be easily imported into third-party programs for further processing.
All set parameters are stored in a single human-readable file in XML format.
Instruments and Beamlines
X-ray optical systems: from metrology to Point Spread Function
Show abstract
One of the problems often encountered in X-ray mirror manufacturing is setting proper manufacturing tolerances to
guarantee an angular resolution - often expressed in terms of Point Spread Function (PSF) - as needed by the specific
science goal. To do this, we need an accurate metrological apparatus, covering a very broad range of spatial frequencies,
and an affordable method to compute the PSF from the metrology dataset. In the past years, a wealth of methods, based
on either geometrical optics or the perturbation theory in smooth surface limit, have been proposed to respectively treat
long-period profile errors or high-frequency surface roughness. However, the separation between these spectral ranges is
difficult do define exactly, and it is also unclear how to affordably combine the PSFs, computed with different methods
in different spectral ranges, into a PSF expectation at a given X-ray energy. For this reason, we have proposed a method
entirely based on the Huygens-Fresnel principle to compute the diffracted field of real Wolter-I optics, including
measured defects over a wide range of spatial frequencies. Owing to the shallow angles at play, the computation can be
simplified limiting the computation to the longitudinal profiles, neglecting completely the effect of roundness errors.
Other authors had already proposed similar approaches in the past, but only in far-field approximation, therefore they
could not be applied to the case of Wolter-I optics, in which two reflections occur in sequence within a short range. The
method we suggest is versatile, as it can be applied to multiple reflection systems, at any X-ray energy, and regardless of
the nominal shape of the mirrors in the optical system. The method has been implemented in the WISE code,
successfully used to explain the measured PSFs of multilayer-coated optics for astronomic use, and of a K-B optical
system in use at the FERMI free electron laser.
Specification of x-ray mirrors in terms of system performance: a new twist to an old plot
Show abstract
In the early 1990’s [App. Opt. 32(19), 3344-531 (1993)], Church and Takacs pointed out that the specification of surface
figure and finish of x-ray mirrors must be based on their performance in the beamline optical system. In the present
work, we demonstrate the limitations of specification, characterization, and performance evaluation based on the totally
statistical approach, including root-mean-square (rms) roughness and residual slope variation, evaluated over the spatial
frequency bandwidths that are system specific, and a more refined statistical description of the surface morphology
based on the power spectral density (PSD) distribution. We show that the limitations are fatal, especially, in the case of
highly collimated coherent x-ray beams, like beams from X-ray Free Electron Lasers (XFELs). The limitations arise due
to the deterministic character of the surface profile data for a definite mirror, while the specific correlation properties of
the surface are essential for the performance of the entire x-ray optical system. As a possible way to overcome the
problem, we treat a method, suggested in [Opt. Eng. 51(4), 046501, 2012] and based on an autoregressive moving
average (ARMA) modeling of the slope measurements with a limited number of parameters. The effectiveness of the
approach is demonstrated with an example peculiar to the x-ray optical systems under design at the European XFEL.
Soft matter interfaces beamline at NSLS-II: geometrical ray-tracing vs. wavefront propagation simulations
Show abstract
We report on the implications of the design of a Soft Matter Interfaces beamline, a long energy range canted in-vacuum
undulator (IVU) beamline at National Synchrotron Light Source II, based on comparison of geometrical ray-tracing and
partially coherent x-ray wavefront propagation simulation software packages, namely, SHADOW and Synchrotron
Radiation Workshop (SRW). For SHADOW, we employed an SRW-generated source file which simulated spectralangular
distribution and apparent source characteristics of radiation produced by a 2.8 m long IVU with a 23 mm period
and allowed us to realistically estimate the beam intensity at the sample positions. We highlight the necessity to use
realistic mirror surface profiles with expected slope errors as opposed to “standard” built-in SHADOW surface error
options. The beamline performances at three different x-ray photon energies: 20358 eV, 10778 eV, and 2101 eV, under
different focusing conditions, have been studied. We compare beamline simulations performed with both software
packages. In particular, we stress that the neglect of wavefront diffraction effects in geometrical ray-tracing approach
results in significant discrepancies in beam spot size and beam shape, the correct assessments of which are crucial in
determining the future performance of an instrument.
Partially coherent wavefront propagation simulations for inelastic x-ray scattering beamline including crystal optics
Show abstract
Up to now simulation of perfect crystal optics in the “Synchrotron Radiation Workshop” (SRW) wave-optics computer
code was not available, thus hindering the accurate modelling of synchrotron radiation beamlines containing optical
components with multiple-crystal arrangements, such as double-crystal monochromators and high-energy-resolution
monochromators. A new module has been developed for SRW for calculating dynamical diffraction from a perfect
crystal in the Bragg case. We demonstrate its successful application to the modelling of partially-coherent undulator
radiation propagating through the Inelastic X-ray Scattering (IXS) beamline of the National Synchrotron Light Source II
(NSLS-II) at Brookhaven National Laboratory. The IXS beamline contains a double-crystal and a multiple-crystal highenergy-
resolution monochromator, as well as complex optics such as compound refractive lenses and Kirkpatrick-Baez
mirrors for the X-ray beam transport and shaping, which makes it an excellent case for benchmarking the new
functionalities of the updated SRW codes. As a photon-hungry experimental technique, this case study for the IXS
beamline is particularly valuable as it provides an accurate evaluation of the photon flux at the sample position, using the
most advanced simulation methods and taking into account parameters of the electron beam, details of undulator source,
and the crystal optics.
Wavefront propagation simulations for a UV/soft x-ray beamline: Electron Spectro-Microscopy beamline at NSLS-II
Show abstract
A “source-to-sample” wavefront propagation analysis of the Electron Spectro-Microscopy (ESM) UV / soft X-ray
beamline, which is under construction at the National Synchrotron Light Source II (NSLS-II) in the Brookhaven
National Laboratory, has been conducted. All elements of the beamline - insertion device, mirrors, variable-line-spacing
gratings and slits - are included in the simulations. Radiation intensity distributions at the sample position are displayed
for representative photon energies in the UV range (20 - 100 eV) where diffraction effects are strong. The finite
acceptance of the refocusing mirrors is the dominating factor limiting the spatial resolution at the sample (by ~3 μm at
20 eV). Absolute estimates of the radiation flux and energy resolution at the sample are also obtained from the
electromagnetic calculations. The analysis of the propagated UV range undulator radiation at different deflection
parameter values demonstrates that within the beamline angular acceptance a slightly “red-shifted” radiation provides
higher flux at the sample and better energy resolution compared to the on-axis resonant radiation of the fundamental
harmonic.
Calculation of the instrumental profile function for a powder diffraction beamline used in nanocrystalline material research
Show abstract
Ray-tracing algorithms are used to simulate the instrumental function of a synchrotron beamline targeted to the advanced
characterization of nanocrystalline materials by powder diffraction. The characteristics of the source, a bending magnet
in the present case of study, and the optics influence the instrumental profile, which is a key parameter for obtaining
information on the nanostructure.
We combine the SHADOW simulation with the calculation of powder diffraction profiles from standard materials, into a
high-level workflow environment based on the ORANGE software, allowing us to integrate data analysis fitting software
with realistic information.
Crystal Optics
Perfect crystal propagator for physical optics simulations with Synchrotron Radiation Workshop
Show abstract
Until now, a treatment of dynamical diffraction from perfect crystals has been missing in the "Synchrotron
Radiation Workshop" (SRW) wavefront propagation computer code despite the widespread use of crystals on X-ray synchrotron beamlines. Now a special propagator" module for calculating dynamical diffraction from a perfect crystal in the Bragg case has been written in C++, integrated into the SRW C/C++ library and made available for simulations using the Python interface of SRW. The propagator performs local processing of the frequency-domain electric field in the angular representation. A 2-D Fast Fourier Transform is used for changing the field representation from/to the coordinate representation before and after applying the crystal propagator. This ensures seamless integration of the new propagator with the existing functionalities of the SRW package, allows compatibility with existing propagators for other optical elements, and enables the simulation of complex beamlines transporting partially coherent X-rays. The code has been benchmarked by comparison with predictions made by plane-wave and spherical-wave dynamical diffraction theory. Test simulations for a selection of X-ray synchrotron beamlines are also shown.
Development of spatially resolved high resolution x-ray spectroscopy for fusion and light-source research
Show abstract
One dimensional spatially resolved high resolution x-ray spectroscopy with spherically bent crystals and 2D pixelated
detectors is an established technique on magnetic confinement fusion (MCF) experiments world wide for Doppler
measurements of spatial profiles of plasma ion temperature and flow velocity. This technique is being further developed
for diagnosis of High Energy Density Physics (HEDP) plasmas at laser-plasma facilities and synchrotron/x-ray free
electron laser (XFEL) facilities. Useful spatial resolution (micron scale) of such small-scale plasma sources requires
magnification, because of the finite pixel size of x-ray CCD detectors (13.5 μm). A von-Hamos like spectrometer using
spherical crystals is capable of magnification, as well as uniform sagittal focusing across the full x-ray spectrum, and is
being tested in laboratory experiments using a tungsten-target microfocus (5-10 μm) x-ray tube and 13-μm pixel x-ray
CCD. A spatial resolution better than 10 μm has been demonstrated. Good spectral resolution is indicated by small
differences (0.02 – 0.1 eV) of measured line widths with best available published natural line widths. Progress and status
of HEDP measurements and the physics basis for these diagnostics are presented. A new type of x-ray crystal
spectrometer with a convex spherically bent crystal is also reported. The status of testing of a 2D imaging microscope
using matched pairs of spherical crystals with x rays will also be presented. The use of computational x-ray optics codes
in development of these instrumental concepts is addressed.
Modeling of a compound imaging system with a curved monochromator and polycapillary optics
Show abstract
Monochromatic x-ray beams improve image contrast but suffer from low intensity if produced with a flat
monochromator crystal. A doubly-curved crystal makes more efficient use of the source. However, the beam shape
is not conducive to imaging. A combination of a bent crystal followed by a polycapillary optic can be used to
monochromatize and focus x rays to a small spot to perform monochromatic x-ray imaging with good resolution.
Ray-tracing simulations have been developed which account for defects in both optics types. A comparison was
made to measurements of focal spot sizes, angular divergence, and image quality parameters including resolution
and contrast. Simulations support the experimental results that geometric blur is significantly reduced, and
resolution enhanced, for magnification imaging with this optic combination.
High-Resolution Focusing Optics and Imaging I
Computational techniques in propagation-based x-ray phase imaging
Show abstract
X–ray phase imaging utilizes a variety of techniques to render phase information as intensity contrast and these
intensity images can in some cases be processed to retrieve quantitative phase. A subset of these techniques
use free space propagation to generate phase contrast and phase can be recovered by inverting differential
equations governing propagation. Two techniques to generate quantitative phase reconstructions from a single
phase contrast image are described in detail, along with regularization techniques to reduce the influence of
noise. Lastly, a recently developed technique utilizing a binary–amplitude grid to enhance signal strength in
propagation–based techniques is described.
The finite-difference simulation of x-rays propagation through a system of lenses
Show abstract
The propagation of X-ray waves through an optical system consisting of 33 aluminum X-ray refractive lenses
is considered. For solving the problem, a finite-difference method is suggested and investigated. It is shown
that very small steps of the difference grid are necessary for reliable computation of propagation of X-ray waves
through the system of lenses. It is shown that the wave phase is a function very quickly increasing with distance
from an optical axis, after the wave has propagated through the system of lenses. If the phase is a quickly
increasing function, then the wave electric field is a quickly oscillating function. We suggest and recommend
using the equation for a phase function instead of the equation for an electric field. The equation for a phase
function is derived.
Contrast enhancement of propagation based X-ray phase contrast imaging
Show abstract
We demonstrate a quantitative X-ray phase contrast imaging (XPCI) technique derived from propagation dependent phase change. We assume that the absorption and phase components are correlated and solve the Transport of Intensity Equation (TIE). The experimental setup is simple compared to other XPCI techniques; the only requirements are a micro-focus X-ray source with sufficient temporal coherence and an X-ray detector of sufficient spatial resolution. This method was demonstrated in three scenarios, the first of which entails identification of an index-matched sphere. A rubber and nylon sphere were immersed in water and imaged. While the rubber sphere could be plainly seen on a radiograph, the nylon sphere was only visible in the phase reconstruction. Next, the technique was applied to differentiating liquid samples. In this scenario, three liquid samples (acetone, water, and hydrogen peroxide) were analyzed using both conventional computed tomography (CT) and phase contrast CT. While conventional CT was capable of differentiating between acetone and the other two liquids, it failed to distinguish between water and hydrogen peroxide; only phase CT was capable of differentiating all three samples. Finally, the technique was applied to CT imaging of a human artery specimen with extensive atherosclerotic plaque. This scenario demonstrated the increased sensitivity to soft tissue compared to conventional CT; it also uncovered some drawbacks of the method, which will be the target of future work. In all cases, the signal-to-noise ratio of phase contrast was greatly enhanced relative to conventional attenuation-based imaging.
High-Resolution Focusing Optics and Imaging II
3D x-ray reconstruction using lightfield imaging
Show abstract
Existing Computed Tomography (CT) systems require full 360 rotation projections. Using the principles of lightfield
imaging, only 4 projections under ideal conditions can be sufficient when the object is illuminated with multiple-point Xray
sources. The concept was presented in a previous work with synthetically sampled data from a synthetic phantom.
Application to real data requires precise calibration of the physical set up. This current work presents the calibration
procedures along with experimental findings for the reconstruction of a physical 3D phantom consisting of simple
geometric shapes. The crucial part of this process is to determine the effective distances of the X-ray paths, which are not
possible or very difficult by direct measurements. Instead, they are calculated by tracking the positions of fiducial
markers under prescribed source and object movements. Iterative algorithms are used for the reconstruction. Customized
backprojection is used to ensure better initial guess for the iterative algorithms to start with.
Developments of x-ray grating imaging and trying of multiple information fusion
Show abstract
The present paper reviews the X-ray grating imaging systems at home and abroad from the aspects of technological
characterizations and the newest researching focus. First, not only the imaging principles and the frameworks of the typical
X-ray grating imaging system based on Talbot-Lau interferometry method, but also the algorithms of retrieving the signals
of attenuation, refraction and small-angle scattering are introduced. Second, the system optimizing methods are discussed,
which involves mainly the relaxing the requirement of high positioning resolution and strict circumstances for gratings and
designing large field of view with high resolution. Third, two and four-dimensional grating-based X-ray imaging techniques
are introduced. Moreover, the trends of X-ray grating based imaging technology are discussed, especially the multiple
information fusions are tried with attenuation, refraction and scattering obtained synchronously.
Poster Session
Separation of hard x-ray synchrotron radiation from electron beam slices
Show abstract
In the electron beam slicing scheme1, 2 considered for National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory, when a low energy electron bunch crosses from top of a high energy storage ring electron bunch, its coulomb force will kick a short slice (slicing bunch) from the core (core bunch) of the storage ring electron bunch. The short slice bunch and the long core bunch when passing through the 3 m long U20 in-vacuum undulator will radiate X-ray pulses with pulse length ~150 fs and 30 ps respectively. To separate the satellite radiation from the core radiation, we propose a conceptual optical scheme allowing for the separation. To get reliable estimates of the separation performances, we apply the Synchrotron Radiation Workshop (SRW) physical optics computer code3, 4 to study the wavefront propagation. As calculations show, at 7.8 keV, the separation signal-to-noise ratio can reach 5~12 and the satellite photon flux per pulse at sample can be 5000~20000 photons/0.1%BW with x-ray pulse length 150 ~ 330 fs depending on the separation method and the crossing angle between the low energy electron bunch and the high energy storage ring bunch. Since the repetition rate of the electron beam slicing system can reach 100 kHz, the average flux per second can reach 5 x 108 ` 2 x 109
photons/sec/0.1%BW.
A proposal for an open source graphical environment for simulating x-ray optics
Show abstract
A new graphic environment to drive X-ray optics simulation packages such as SHADOW and SRW is proposed. The
aim is to simulate a virtual experiment, including the description of the electron beam and simulate the emitted
radiation, the optics, the scattering by the sample and radiation detection. Python is chosen as common interaction
language. The ingredients of the new application, a glossary of variables for optical component, the selection of
visualization tools, and the integration of all these components in a high level workflow environment built on Orange
are presented.
Simulation of the ultrahigh energy resolution IXS analyzer system at NSLS-II
Alexey Suvorov,
David S. Coburn,
Alessandro Cunsolo,
et al.
Show abstract
The ultrahigh energy resolution IXS spectrometer being developed at the National Synchrotron Light Source II (NSLSII)
employs an innovative optical design. Its analyzer system utilizes an L-shaped laterally graded multilayer mirror in
tandem with a multi-crystal arrangement. The multi-crystal arrangement explores the angular dispersion effect in
extremely asymmetric Bragg reflections to achieve sub-meV energy resolution at an energy about 9.1 keV. Its angular
acceptance (~ 0.1 mrad) is about two orders of magnitude lower than the spherically-bent backscattering analyzers
conventionally used in other IXS spectrometers. The L-shaped laterally graded multiplayer mirror was designed to
increase the angular acceptance of this new multi-crystal optics to a comparable level. It performs angular collimation of
the incoming beam from about 15 mrad down to 0.1 mrad in both vertical and horizontal directions. Here we present
simulations of the mirror performance and study the positioning and stability requirements in conjunction with the multicrystal
energy analyzer.
An open software framework for advancement of x-ray optics simulation and modeling
Show abstract
Accurate physical-optics based simulation of emission, transport and use in experiments of fully- and partially-coherent
X-ray radiation is essential for both designers and users of experiments at state-of-the-art light sources: low-emittance
storage rings, energy-recovery linacs and free-electron lasers. To be useful for different applications, the simulations
must include accurate physical models for the processes of emission, for the structures of X-ray optical elements,
interaction of the radiation with samples, and propagation of scattered X-rays to a detector. Based on the “Synchrotron
Radiation Workshop” (SRW) open source computer code, we are developing a simulation framework, including a
graphical user interface, web interface for client-server simulations, data format for wave-optics based representation of
partially-coherent X-ray radiation, and a dictionary for universal description of optical elements. Also, we are evaluating
formats for sample and experimental data representation for different types of experiments and processing. The
simulation framework will facilitate start-to-end simulations by different computer codes complementary to SRW, for
example GENESIS and FAST codes for simulating self-amplified spontaneous emission, SHADOW and McXtrace
geometrical ray-tracing codes, as well as codes for simulation of interaction of radiation with matter and data processing
in experiments exploiting coherence of radiation. The development of the new framework is building on components
developed for the Python-based RadTrack software, which is designed for loose coupling of multiple electron and
radiation codes to enable sophisticated workflows. We are exploring opportunities for collaboration with teams pursuing
similar developments at European Synchrotron Radiation Facility and the European XFEL.
A new SHADOW update: integrating diffraction effects into ray-tracing
Show abstract
We describe the new implementation in the ray-tracing code SHADOW based on a “hybrid method” developed
recently. The code calculates the diffraction effects from an optical element by means of wavefront propagation,
and combines the result with that from regular ray-tracing. This hybrid procedure is invoked when diffraction is
present (e.g., beam clipped by an aperture or the finite size of the optics) by user demand. The code enables the
simulation of mirror figure errors in the framework of wave optics. The simulation of a complete beamline based
on the far-field approximation is demonstrated. The near-field propagation is also implemented for individual
optics. Finally, the applicable conditions and limitations of the new code are discussed.
Fourier transform image processing techniques for grid-based phase contrast imaging
Show abstract
A recently developed technique for phase imaging using table top sources is to use multiple fine-pitch gratings.
However, the strict manufacturing tolerences and precise alignment required have limited the widespread adoption
of grating-based techniques. In this work, we employ a technique recently demonstrated by Bennett et al.1 that
ultilizes a single grid of much coarser pitch. Phase is extracted using Fourier processing on a single raw image taken
using a focused mammography grid. The effects on the final image of varying grid, object, and detector distances,
window widths, and of a variety of windowing functions, used to separate the harmonics, were investigated.