X-ray free-electron laser wavefront sensing using the fractional Talbot effect.

Yanwei Liu,Kenan Li,Yiping Feng,Xianbo Shi,Peter Walter,Lahsen Assoufid,Yuantao Ding,Matthew Seaberg,David Fritz,Anne Sakdinawat,Walan Grizolli,Gabriel Marcus

doi:10.1107/s1600577519017107

Yanwei Liu, Kenan Li + Show 10 more

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Wavefront sensing at X-ray free-electron lasers is important for quantitatively understanding the fundamental properties of the laser, for aligning X-ray instruments and for conducting scientific experimental analysis. A fractional Talbot wavefront sensor has been developed. This wavefront sensor enables measurements over a wide range of energies, as is common on X-ray instruments, with simplified mechanical requirements and is compatible with the high average power pulses expected in upcoming X-ray free-electron laser upgrades. Single-shot measurements were performed at 500 eV, 1000 eV and 1500 eV at the Linac Coherent Light Source. These measurements were applied to study both mirror alignment and the effects of undulator tapering schemes on source properties. The beamline focal plane position was tracked to an uncertainty of 0.12 mm, and the source location for various undulator tapering schemes to an uncertainty of 1 m, demonstrating excellent sensitivity. These findings pave the way to use the fractional Talbot wavefront sensor as a routine, robust and sensitive tool at X-ray free-electron lasers as well as other high-brightness X-ray sources.

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IntroductionAs X-ray free-electron lasers (FELs) (Kim et al, 2017; Pellegrini et al, 2016; Attwood & Sakdinawat, 2017) and synchrotron sources (Attwood & Sakdinawat, 2017; Eriksson et al, 2014) continue to evolve with the ability to produce more distinctive X-ray beam properties, X-ray wavefront sensing (Chalupskyet al., 2010; David et al, 2011; Idir et al, 2014; Keitel et al, 2016; Rutishauser et al, 2012; Kayser et al, 2016; Berujon et al, 2015) becomes increasingly important for gaining a fundamental understanding of these beams and providing the required feedback for their manipulation
Two common wavefront sensors (WFS) currently being utilized at free-electron lasers (FELs) are ones based on the Talbot grating interferometer (Pfeiffer et al, 2005; Rutishauser et al, 2012; Kayser et al, 2016; Assoufid et al, 2016; Matsuyama et al, 2012; Liu et al, 2018), which have primarily been used for hard X-rays, and ones based on the Hartmann wavefront sensor (Idir et al, 2014; Keitel et al, 2016), which have primarily been used in the extreme ultraviolet regime
The fractional Talbot WFS was implemented at the AMO instrument at Linac Coherent Light Source (LCLS) (Osipov et al, 2018)

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Introduction

As X-ray free-electron lasers (FELs) (Kim et al, 2017; Pellegrini et al, 2016; Attwood & Sakdinawat, 2017) and synchrotron sources (Attwood & Sakdinawat, 2017; Eriksson et al, 2014) continue to evolve with the ability to produce more distinctive X-ray beam properties, X-ray wavefront sensing (Chalupskyet al., 2010; David et al, 2011; Idir et al, 2014; Keitel et al, 2016; Rutishauser et al, 2012; Kayser et al, 2016; Berujon et al, 2015) becomes increasingly important for gaining a fundamental understanding of these beams and providing the required feedback for their manipulation. Accurate knowledge of the wavefront allows feedback to the optics for proper alignment, diffraction-limited focusing and sample-beam alignment

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