Focus characterization of an X-ray free-electron laser by intensity correlation measurement of X-ray fluorescence

Nakamura, Nobutomo; Matsuyama, Satoshi; Inoue, Takato; Inoue, Ituro; Yamada, Jumpei; Osaka, Taito; Yabashi, Makina; Ishikawa, Tetsuya; Yamauchi, Kazuto

doi:10.1107/s1600577520009868

Cited by 8 publications

(6 citation statements)

References 31 publications

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“…To ensure that the sample wasn't damaged from the pulses, the copper foil was rotated such that each pulse illuminated a new area. Although the combined fluorescence image was isotropic and contained no structural information, the constructed g (2) revealed interference fringes reaching the third-order peaks, which is an improvement compared to previous studies that only measured the zero-order peak in g (2) [6,7]. By using an iterative algorithm, the researchers successfully reconstructed the size (300 nm) and separation (860 nm) of the two excited spots on the copper film.…”

Section: Credit: Stacy Huangmentioning

confidence: 93%

Bringing Interferometric Imaging into the X-Ray Regime

2023

Physics

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Section: Credit: Stacy Huangmentioning

confidence: 93%

Bringing Interferometric Imaging into the X-Ray Regime

2023

Physics

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“…There are already some methods for characterizing the spot through analysis of the speckle or fluorescence. Spatiotemporal coherence, energy and spot size of XFELs have been analyzed by the scattering of single or multiple particles (Inoue et al, 2015;Yun et al, 2019;Lee et al, 2020;Nakamura et al, 2020). These methods are meaningful in XFEL pulse diagnosis.…”

Section: Introductionmentioning

confidence: 99%

Single-pulse characterization of the focal spot size of X-ray free-electron lasers using coherent diffraction imaging

Gao¹,

Fan²,

Tong³

et al. 2023

J Synchrotron Radiat

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The characterization of X-ray focal spots is of great significance for the diagnosis and performance optimization of focusing systems. X-ray free-electron lasers (XFELs) are the latest generation of X-ray sources with ultrahigh brilliance, ultrashort pulse duration and nearly full transverse coherence. Because each XFEL pulse is unique and has an ultrahigh peak intensity, it is difficult to characterize its focal spot size individually with full power. Herein, a method for characterizing the spot size at the focus position is proposed based on coherent diffraction imaging. A numerical simulation was conducted to verify the feasibility of the proposed method. The focal spot size of the Coherent Scattering and Imaging endstation at the Shanghai Soft X-ray Free Electron Laser Facility was characterized using the method. The full width at half-maxima of the focal spot intensity and spot size in the horizontal and vertical directions were calculated to be 2.10 ± 0.24 µm and 2.00 ± 0.20 µm, respectively. An ablation imprint on the silicon frame was used to validate the results of the proposed method.

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“…From this alone, one can confirm experimental conditions for IDI, compare the fluorescence lifetimes of atoms and atomic states (such as in different chemical environments or physical environments), or compare pulse durations of different operating modes of an X-ray free-eletron laser (FEL) (Inoue et al, 2019). Knowledge of the speckle contrast can be used to tune the X-ray source to maximize peak brightness of pulses, or to find the location of highest intensity of a focused beam (Nakamura et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Speckle contrast of interfering fluorescence X-rays

Trost¹,

Ayyer²,

Oberthüer³

et al. 2023

J Synchrotron Radiat

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With the development of X-ray free-electron lasers (XFELs), producing pulses of femtosecond durations comparable with the coherence times of X-ray fluorescence, it has become possible to observe intensity–intensity correlations due to the interference of emission from independent atoms. This has been used to compare durations of X-ray pulses and to measure the size of a focusedX-ray beam, for example. Here it is shown that it is also possible to observe the interference of fluorescence photons through the measurement of the speckle contrast of angle-resolved fluorescence patterns. Speckle contrast is often used as a measure of the degree of coherence of the incident beam or the fluctuations of the illuminated sample as determined from X-ray diffraction patterns formed by elastic scattering, rather than from fluorescence patterns as addressed here. Commonly used approaches to estimate speckle contrast were found to suffer when applied to XFEL-generated fluorescence patterns due to low photon counts and a significant variation of the excitation pulse energy from shot to shot. A new method to reliably estimate speckle contrast under such conditions, using a weighting scheme, is introduced. The method is demonstrated by comparing the speckle contrast of fluorescence observed with pulses of 3 fs to 15 fs duration.

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Focus characterization of an X-ray free-electron laser by intensity correlation measurement of X-ray fluorescence

Cited by 8 publications

References 31 publications

Bringing Interferometric Imaging into the X-Ray Regime

Bringing Interferometric Imaging into the X-Ray Regime

Single-pulse characterization of the focal spot size of X-ray free-electron lasers using coherent diffraction imaging

Speckle contrast of interfering fluorescence X-rays

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