Abstract
The Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL) is a recently commissioned X-ray free-electron laser (XFEL) facility that provides intense ultrashort X-ray pulses based on the self-amplified spontaneous emission process. The nano-crystallography and coherent imaging (NCI) hutch with forward-scattering geometry is located at the hard X-ray beamline of the PAL-XFEL and provides opportunities to perform serial femtosecond crystallography and coherent X-ray diffraction imaging. To produce intense high-density XFEL pulses at the interaction positions between the X-rays and various samples, a microfocusing Kirkpatrick-Baez (KB) mirror system that includes an ultra-precision manipulator has been developed. In this paper, the design of a KB mirror system that focuses the hard XFEL beam onto a fixed sample point of the NCI hutch, which is positioned along the hard XFEL beamline, is described. The focusing system produces a two-dimensional focusing beam at approximately 2 µm scale across the 2-11 keV photon energy range. XFEL pulses of 9.7 keV energy were successfully focused onto an area of size 1.94 µm × 2.08 µm FWHM.
Highlights
In the X-ray regime, X-ray free-electron lasers (XFELs) produce unprecedented levels of brilliance, excellent spatial coherence and ultrafast pulse durations (McNeil & Thompson, 2010)
The carbon-coated area is intended for experiments requiring high photon flux, while the non-coated area is used for coherent diffraction imaging experiments requiring speckle-free XFEL pulses
The XFEL pulses used in this study were generated by a polychromatic X-ray passing through the offset mirrors (OMs) at the optical hutch (OH)
Summary
In the X-ray regime, X-ray free-electron lasers (XFELs) produce unprecedented levels of brilliance, excellent spatial coherence and ultrafast pulse durations (McNeil & Thompson, 2010). These unique properties provide opportunities to observe materials with high resolution, or facilitate radiation-damage-free and time-resolved studies using ultrashort pulse widths (Neutze et al, 2000; McNeil & Thompson, 2010). In terms of XFEL facilities, the Linac Coherent Light Source (LCLS) (Emma et al, 2010) and SPring-8 Angstrom Compact free-electron LAser (SACLA) (Ishikawa et al, 2012) facilities are both successfully operating hard XFELs. Recently, the Pohang Accelerator Laboratory (PAL-XFEL) (Ko et al, 2017) and the European XFEL (Decking & Limberg, 2013) completed self-amplified spontaneous emission (SASE) commissioning and are in operation.
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