Generation of an X-ray nanobeam of a free-electron laser using reflective optics with speckle interferometry.

Takato Inoue,Haruhiko Ohashi,Satoshi Matsuyama,Kensuke Tono,Jumpei Yamada,Nami Nakamura,Hirokatsu Yumoto,Takahisa Koyama,Ichiro Inoue,Makina Yabashi,Tetsuya Ishikawa,Taito Osaka,Kazuto Yamauchi,Yuichi Inubushi

doi:10.1107/s1600577520006980

Abstract

Ultimate focusing of an X-ray free-electron laser (XFEL) enables the generation of ultrahigh-intensity X-ray pulses. Although sub-10 nm focusing has already been achieved using synchrotron light sources, the sub-10 nm focusing of XFEL beams remains difficult mainly because the insufficient stability of the light source hinders the evaluation of a focused beam profile. This problem is specifically disadvantageous for the Kirkpatrick-Baez (KB) mirror focusing system, in which a slight misalignment of ∼300 nrad can degrade thefocused beam. In this work, an X-ray nanobeam of a free-electron laser wasgenerated using reflective KB focusing optics combined with speckle interferometry. The speckle profiles generated by 2 nm platinum particles were systematically investigated on a single-shot basis by changing the alignment of the multilayer KB mirror system installed at the SPring-8 Angstrom Compact Free-Electron Laser, in combination with computer simulations. It was verified that the KB mirror alignments were optimized with the required accuracy, and a focused vertical beam of 5.8 nm (±1.2 nm) was achieved after optimization. The speckle interferometry reported in this study is expected to be an effective tool for optimizing the alignment of nano-focusing systems and for generating an unprecedented intensity of up to 1022 W cm-2 using XFEL sources.

Highlights

X-ray free-electron lasers (XFELs) (Emma et al, 2010; Ishikawa et al, 2012; Kang et al, 2017; Tschentscher et al, 2017) possess unique properties, such as unprecedented peak brilliance, nearly full spatial coherence, and an ultrashort pulse duration, compared with the conventional X-ray sources
The high intensity generated by focusing the XFEL beams allows us to study the nonlinear phenomena in the X-ray region and the highenergy-density states in matter (Wehrenberg et al, 2017)
We present the generation of an XFEL nanobeam by optimizing the Kirkpatrick– Baez (KB) mirror alignment using speckles

Summary

Introduction

X-ray free-electron lasers (XFELs) (Emma et al, 2010; Ishikawa et al, 2012; Kang et al, 2017; Tschentscher et al, 2017) possess unique properties, such as unprecedented peak brilliance, nearly full spatial coherence, and an ultrashort pulse duration, compared with the conventional X-ray sources. This novel light source has created new opportunities in various fields of science, such as non-destructive observation of objects based on the ‘diffraction-before-destruction’ scheme (Neutze et al, 2000; Chapman et al, 2011; Kimura et al, 2014), and observation of molecular dynamics and ultrafast phenomena (Picon et al, 2016). We provide experimental evidence that an XFEL of less than 10 nm was attained at SACLA

Theory of beam diagnosis using speckles by coherent scattering

Relationship between mirror misalignments and beam profile

Relationship between speckle profile and misalignments

Experiment

Results and discussion

Funding information