Hard X-ray nanofocusing at low-emittance synchrotron radiation sources

Schroer, Christian G.; Falkenberg, Gerald

doi:10.1107/s1600577514016269

Cited by 33 publications

(32 citation statements)

References 29 publications

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“…Previous studies [17,20,21] of the effect of PE escape have often incorporated Monte Carlo (MC) modelling of electron trajectories, performed using programmes such as CASINO [23,24]. In the current paper, we present the first systematic simulation study of PE escape in MX accounting for: (1) the effects of a finite beam size comparable to the PE stopping range; (2) the effects of a finite crystal size matched to the FWHM of the beam; (3) the effect of variation in X-ray beam energy; and (4) the influence of the beam profile as a function of the dose received by the crystal over time.…”

Section: Introductionmentioning

confidence: 99%

“…These results did not account for PE escape and were independent of beam and crystal size. (2) DE NoPE values were calculated as the ratio of the number of coherently scattered photons per unit volume, N C /σ 3 X , to the average global dose, D G , based on results of our simulations that did not account for PE escape-this included both our control simulations and simulations that used RADDOSE-3D dose maps. DE NoPE was insensitive to changes in beam and crystal size; within each set (RADDOSE-3D, control) results at 30 keV showed a standard deviation of 3% from the average, with averages at all other energies showing a standard deviation of less than 1%.…”

Section: Variation Of Diffraction Efficiency With Energymentioning

confidence: 99%

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The Influence of Photoelectron Escape in Radiation Damage Simulations of Protein Micro-Crystallography

2018

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Radiation damage represents a fundamental limit in the determination of protein structures via macromolecular crystallography (MX) at third-generation synchrotron sources. Over the past decade, improvements in both source and detector technology have led to MX experiments being performed with smaller and smaller crystals (on the order of a few microns), often using microfocus beams. Under these conditions, photoelectrons (PEs), the primary agents of radiation-damage in MX, may escape the diffraction volume prior to depositing all of their energy. The impact of PE escape is more significant at higher beam energies (>20 keV) as the electron inelastic mean free path (IMFP) is longer, allowing the electrons to deposit their energy over a larger area, extending further from their point of origin. Software such as RADDOSE-3D has been used extensively to predict the dose (energy absorbed per unit mass) that a crystal will absorb under a given set of experimental parameters and is an important component in planning a successful MX experiment. At the time this study was undertaken, dose predictions made using RADDOSE-3D were spatially-resolved, but did not yet account for the propagation of PEs through the diffraction volume. Hence, in the case of microfocus crystallography, it is anticipated that deviations may occur between the predicted and actual dose absorbed due to the influence of PEs. To explore this effect, we conducted a series of simulations of the dose absorbed by micron-sized crystals during microfocus MX experiments. Our simulations spanned beam and crystal sizes ranging from 1 µm to 5 µm for beam energies between 9 keV and 30 keV. Our simulations were spatially and temporarily resolved and accounted for the escape of PEs from the diffraction volume. The spatially-resolved dose maps produced by these simulations were used to predict the rate of intensity loss in a Bragg spot, a key metric for tracking global radiation damage. Our results were compared to predictions obtained using a recent version of RADDOSE-3D that did not account for PE escape; the predicted crystal lifetimes are shown to differ significantly for the smallest crystals and for high-energy beams, when PE escape is included in the simulations.

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Section: Introductionmentioning

confidence: 99%

Section: Variation Of Diffraction Efficiency With Energymentioning

confidence: 99%

The Influence of Photoelectron Escape in Radiation Damage Simulations of Protein Micro-Crystallography

2018

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“…This approximation is based on the fact that electrons in an undulator source radiate in a random and uncorrelated fashion to each other. A recent study shows that one can approximate the central cone of electromagnetic radiation from an undulator source by an ensemble of Gaussian limited waves [20]. Nevertheless, some researchers suggest by incorporation of a higher-order of intensity correlation functions, the in-tegrated spectral of electromagnetic wave can be either Gaussian or non-Gaussian distributions [21].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of partial coherence correction in X-ray ptychography

Burdet¹,

Shi²,

Parks

et al. 2015

Opt. Express

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Coherent X-ray Diffraction Imaging (CDI) and X-ray ptychography both heavily rely on the high degree of spatial coherence of the X-ray illumination for sufficient experimental data quality for reconstruction convergence. Nevertheless, the majority of the available synchrotron undulator sources have a limited degree of partial coherence, leading to reduced data quality and a lower speckle contrast in the coherent diffraction patterns. It is still an open question whether experimentalists should compromise the coherence properties of an X-ray source in exchange for a higher flux density at a sample, especially when some materials of scientific interest are relatively weak scatterers. A previous study has suggested that in CDI, the best strategy for the study of strong phase objects is to maintain a high degree of coherence of the illuminating X-rays because of the broadening of solution space resulting from the strong phase structures. In this article, we demonstrate the first systematic analysis of the effectiveness of partial coherence correction in ptychography as a function of the coherence properties, degree of complexity of illumination (degree of phase diversity of the probe) and sample phase complexity. We have also performed analysis of how well ptychographic algorithms refine X-ray probe and complex coherence functions when those variables are unknown at the start of reconstructions, for noise-free simulated data, in the case of both real-valued and highly-complex objects. K. Robinson, "Shearing interferometer for quantifying the coherence of hard x-ray beams," Phys. Rev. Lett. 94, 164801 (2005). 30.

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“…We now comment on the chosen values of the rms size (11) and divergence (10), which depend on how one fits the undulator field (13) [17], from which the effective Rayleigh range of undulator radiation was determined to be Z…”

Section: A Paraxial Description Of Undulator Radiationmentioning

confidence: 99%

“…In tandem with these developments, a host of experimental x-ray techniques have been developed over the last few decades that take advantage of partially coherent radiation, including x-ray photon correlation spectroscopy and scattering [5,6], coherent x-ray diffractive imaging [7][8][9], x-ray scanning microscopy [10], and x-ray nanoprobe spectroscopy [11]. The ability to make detailed predictions of the x-ray properties has become an important component in both the design and interpretation of these experiments.…”

Section: Introductionmentioning

confidence: 99%

Compact representations of partially coherent undulator radiation suitable for wave propagation

Lindberg

Kim

2015

Phys. Rev. ST Accel. Beams

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Undulator radiation is partially coherent in the transverse plane, with the degree of coherence depending on the ratio of the electron beam phase space area (emittance) to the characteristic radiation wavelength λ. On the other hand, numerical codes used to predict x-ray beam line performance can typically only propagate coherent fields from the source to the image plane. We investigate methods for representing partially coherent undulator radiation using a suitably chosen set of coherent fields that can be used in standard wave propagation codes, and discuss such "coherent mode expansions" for arbitrary degrees of coherence. In the limit when the electron beam emittance along at least one direction is much larger than λ the coherent modes are orthogonal and therefore compact; when the emittance approaches λ in both planes we discuss an economical method of defining the relevant coherent fields that samples the electron beam phase space using low-discrepancy sequences.

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Hard X-ray nanofocusing at low-emittance synchrotron radiation sources

Cited by 33 publications

References 29 publications

The Influence of Photoelectron Escape in Radiation Damage Simulations of Protein Micro-Crystallography

The Influence of Photoelectron Escape in Radiation Damage Simulations of Protein Micro-Crystallography

Evaluation of partial coherence correction in X-ray ptychography

Compact representations of partially coherent undulator radiation suitable for wave propagation

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