Abstract
A nanofocusing optical system—referred to as 100 exa—for an X-ray free-electron laser (XFEL) was developed to generate an extremely high intensity of 100 EW/cm2 (1020 W/cm2) using total reflection mirrors. The system is based on Kirkpatrick-Baez geometry, with 250-mm-long elliptically figured mirrors optimized for the SPring-8 Angstrom Compact Free-Electron Laser (SACLA) XFEL facility. The nano-precision surface employed is coated with rhodium and offers a high reflectivity of 80%, with a photon energy of up to 12 keV, under total reflection conditions. Incident X-rays on the optics are reflected with a large spatial acceptance of over 900 μm. The focused beam is 210 nm × 120 nm (full width at half maximum) and was evaluated at a photon energy of 10 keV. The optics developed for 100 exa efficiently achieved an intensity of 1 × 1020 W/cm2 with a pulse duration of 7 fs and a pulse energy of 150 μJ (25% of the pulse energy generated at the light source). The experimental chamber, which can provide different stage arrangements and sample conditions, including vacuum environments and atmospheric-pressure helium, was set up with the focusing optics to meet the experimental requirements.
Highlights
Hard X-ray free-electron laser (XFEL) sources [1,2,3,4,5] have successfully generated extremely high-peak brilliance unachieved by existing synchrotron radiation sources
We report the development of a highly stable, high-throughput focusing system that achieves a high intensity of 1 × 1020 W/cm2 by utilizing single-stage K-B optics optimized for BL3 of SPring-8 Angstrom Compact Free-Electron Laser (SACLA)
The properties of the focused beam were evaluated at EH5, BL3 of SACLA
Summary
Hard X-ray free-electron laser (XFEL) sources [1,2,3,4,5] have successfully generated extremely high-peak brilliance unachieved by existing synchrotron radiation sources. There have been several reports on hard XFEL focusing optics for producing high-intensity pulses utilizing diffractive [6,7], reflective [8,9] and refractive [10,11] optics. Laser (SACLA) XFEL facility [2] This optics system utilized nano-precision figured mirrors with an elliptical cylinder shape in Kirkpatrick-Baez (K-B) geometry [12]. Two-stage focusing optics have successfully contributed to the observation of nonlinear X-ray optical phenomena [13,14,15,16], we encountered several practical challenges in the operation of this system (such as stability, repeatability and alignment) because the focusing condition of the system is highly sensitive to mirror misalignment
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