Automated alignment of XFEL nanofocusing mirrors via wavefront optimization

Area of Science:

• Optics and Photonics
• X-ray Science
• Instrumentation

Background:

• Precise alignment of Kirkpatrick-Baez mirrors is crucial for nanofocusing X-ray free-electron laser (XFEL) beams.
• Aberrations and misalignment degrade focal spot size and intensity, impacting experimental results.

Purpose of the Study:

• To develop an automated alignment procedure for Kirkpatrick-Baez nanofocusing mirrors.
• To optimize focus size, maximize peak intensity, and minimize aberrations for XFEL applications.

Main Methods:

• Wavefront measurement using a single-grating interferometer.
• Quantitative correlation of wavefront errors with alignment deviations (incidence angle, perpendicularity, astigmatism) via Legendre polynomial analysis.
• Automated correction of alignment errors through an optimization process.

Main Results:

• The automated system consistently achieves reproducible XFEL foci below 150 nm × 200 nm.
• Optimal nanofocusing conditions are restored within 10 minutes.
• Legendre polynomial analysis effectively quantifies alignment errors.

Conclusions:

• The developed automated alignment procedure is reliable and efficient for XFEL nanofocusing mirrors.
• This method enables rapid restoration of optimal experimental conditions.
• The system demonstrates practical utility in routine operation at facilities like SACLA.