8 October 2014 Intensity interferometry measurements with hard x-ray FEL pulses at the Linac Coherent Light Source
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Abstract
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, Diling Zhu, Andrej Singer, Juhao Wu, Marcin Sikorski, Matthieu Chollet, Henrik Lemke, Roberto Alonso-Mori, James M. Glownia, Jacek Krzywinski, Alberto Lutman, Yuantao Ding, Timothy Maxwell, James L. Turner, Oleg Gorobtsov, Ivan A. Vartanyants, Aymeric Robert, 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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