Nanofocusing optics for an X-ray free-electron laser generating an extreme intensity of 100 EW/cm$^2$ using total reflection mirrors

TL;DR

This paper reports the development of a nanofocusing optical system for an XFEL that achieves an extremely high intensity of 100 EW/cm$^2$ using total reflection mirrors with nanometer precision.

Contribution

The authors designed and implemented a novel nanofocusing optics system with high reflectivity and precision, enabling unprecedented X-ray intensities at the SACLA facility.

Findings

Achieved an intensity of 10^20 W/cm^2 with 7 fs pulse duration.

Focused beam size of 210 nm by 120 nm at 10 keV.

System demonstrated high reflectivity and large acceptance for efficient focusing.

Abstract

A nanofocusing optical system referred to as $\textit{100 exa}$ for an X-ray free-electron laser (XFEL) was developed to generate an extremely high intensity of 100 EW/cm$^2$ (10$^2$$^0$ W/cm$^2$) using total reflection mirrors. The system is based on Kirkpatrick-Baez geometry, with 250 mm long elliptically figured mirrors optimized for the SPring-8 Angstrom Compact Free-Electron Laser (SACLA) XFEL facility. The nano-precision surface employed is coated with rhodium and offers a high reflectivity of 80%, with a photon energy of up to 12 keV, under total reflection conditions. Incident X-rays on the optics are reflected with a large spatial acceptance of over 900 $\mu$m. The focused beam is 210 nm $\times$ 120 nm (full width at half maximum) and was evaluated at a photon energy of 10 keV. The optics developed for $\textit{100 exa}$ efficiently achieved an intensity of 1 $\times$ 10$^2$$^0$ W/cm$^2$ with a pulse duration of 7 fs and a pulse energy of 150 $\mu$J (25% of the pulse energy generated at the light source). The experimental chamber, which can provide varied stage arrangements and sample conditions, including vacuum environments and atmospheric pressure helium, was set up with the focusing optics to meet the experimental requirements.