Focusing mirror for x-ray free-electron lasers

Area of Science:

• Optics and photonics
• Materials science
• Particle accelerators

Background:

• X-ray free-electron lasers (XFELs) produce intense, coherent beams crucial for advanced research.
• Focusing XFEL beams to nanometer dimensions is challenging but essential for high-resolution imaging and material analysis.
• Existing focusing optics often struggle to meet the stringent requirements for nanometer-scale focusing of XFELs.

Purpose of the Study:

• To design, fabricate, and evaluate a large total-reflection mirror for nanometer focusing of XFEL beams.
• To achieve high figure accuracy and surface smoothness for precise beam manipulation.
• To characterize the performance of the mirror in focusing XFEL beams at a synchrotron facility.

Main Methods:

• Fabrication of a 400 mm long elliptical silicon mirror with a 550 mm focal length.
• Utilized electrolytic in-process dressing grinding for initial figuring.
• Employed elastic emission machining for final figuring and surface smoothing to achieve 2 nm peak-to-valley accuracy.

Main Results:

• Achieved a figure accuracy of 2 nm peak-to-valley across the entire mirror surface.
• Successfully focused a 15 keV XFEL beam to a size of 75 nm at SPring-8.
• The achieved focused beam size closely matched the theoretical diffraction limit.

Conclusions:

• The developed large total-reflection mirror is highly effective for nanometer focusing of XFEL beams.
• The combination of advanced figuring techniques enables unprecedented optical precision for X-ray applications.
• This technology paves the way for enhanced resolution in XFEL-based scientific investigations.