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DOE OSTI · 2006432

Speckle contrast of interfering fluorescence X-rays

Trost, Fabian·Ayyer, Kartik·Oberthuer, Dominik·Yefanov, Oleksandr·Bajt, Saša·Caleman, Carl·Weimer, Agnes·Feld, Artur·Weller, Horst·Boutet, Sébastien·Koglin, Jason·Timneanu, Nicusor·von Zanthier, Joachim·Röhlsberger, Ralf·Chapman, Henry N.
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Abstract

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 focused X-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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73 NUCLEAR PHYSICS AND RADIATION PHYSICSX-ray fluorescenceXPCSincoherent diffraction imagingspeckle contrast estimation

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Trost, Fabian, Ayyer, Kartik, Oberthuer, Dominik, Yefanov, Oleksandr, Bajt, Saša, Caleman, Carl, Weimer, Agnes, Feld, Artur, Weller, Horst, Boutet, Sébastien, Koglin, Jason, Timneanu, Nicusor, von Zanthier, Joachim, Röhlsberger, Ralf, Chapman, Henry N.. 2023-01-01. Speckle contrast of interfering fluorescence X-rays. https://doi.org/10.1107/s1600577522009997

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