8 October 2014 Intensity interferometry measurements with hard x-ray FEL pulses at the Linac Coherent Light Source
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Intensity interferometry measurements were carried out to study the spatial coherence properties of a Free-Electron Laser (FEL) in the Self-Amplified Spontaneous Emission (SASE) mode in the hard X-ray regime. Statistical analyses based on ensemble averages of the spatial intensity correlation function were performed on a large number of pulses, overcoming challenges associated with the FEL beam being non-stationary in time and highly collimated. The second-order intensity correlation functions consistently show deviations from unity, reminiscent of the classical Hanbury-Brown and Twiss effect. They also exhibit a slow decaying spatial dependence at length-scales larger than the width of the beam, indicating a high degree of spatial coherence. These measurements are consistent with the behavior of a highly brilliant but chaotic source obeying Gaussian statistics as expected for a SASE FEL. Our study could be used to devise an in-line diagnostic capable of providing quasi real-time feedback for understanding and tuning the FEL process.
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Sanghoon Song, Sanghoon Song, Diling Zhu, Diling Zhu, Andrej Singer, Andrej Singer, Juhao Wu, Juhao Wu, Marcin Sikorski, Marcin Sikorski, Matthieu Chollet, Matthieu Chollet, Henrik Lemke, Henrik Lemke, Roberto Alonso-Mori, Roberto Alonso-Mori, James M. Glownia, James M. Glownia, Jacek Krzywinski, Jacek Krzywinski, Alberto Lutman, Alberto Lutman, Yuantao Ding, Yuantao Ding, Timothy Maxwell, Timothy Maxwell, James L. Turner, James L. Turner, Oleg Gorobtsov, Oleg Gorobtsov, Ivan A. Vartanyants, Ivan A. Vartanyants, Aymeric Robert, Aymeric Robert, Yiping Feng, Yiping Feng, "Intensity interferometry measurements with hard x-ray FEL pulses at the Linac Coherent Light Source", Proc. SPIE 9210, X-Ray Free-Electron Lasers: Beam Diagnostics, Beamline Instrumentation, and Applications II, 92100M (8 October 2014); doi: 10.1117/12.2069362; https://doi.org/10.1117/12.2069362

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