Speckle contrast of interfering fluorescence X-rays

Trost, F.; Ayyer, K.; Oberthuer, D.; Yefanov, O.; Bajt, S.; Caleman, C.; Weimer, A.; Feld, A.; Weller, H.; Boutet, S.; Koglin, J.; Timneanu, N.; von Zanthier, J.; Röhlsberger, R.; Chapman, H. N.

doi:10.1107/S1600577522009997

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学術論文

Speckle contrast of interfering fluorescence X-rays

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Ayyer, K.
Computational Nanoscale Imaging, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
The Hamburg Center for Ultrafast Imaging, Universität Hamburg;

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https://doi.org/10.1107/S1600577522009997
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引用

Trost, F., Ayyer, K., Oberthuer, D., Yefanov, O., Bajt, S., Caleman, C., Weimer, A., Feld, A., Weller, H., Boutet, S., Koglin, J., Timneanu, N., von Zanthier, J., Röhlsberger, R., & Chapman, H. N. (2023). Speckle contrast of interfering fluorescence X-rays. Journal of Synchrotron Radiation, 30(1), 11-23. doi:10.1107/S1600577522009997.

引用: https://hdl.handle.net/21.11116/0000-000B-7E92-3

要旨

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.