Microfocusing at the PG1 beamline at FLASH.

Area of Science:

• X-ray optics and instrumentation
• Free-electron laser applications
• Spectroscopy

Background:

• The PG1 beamline at the soft X-ray/XUV free-electron laser in Hamburg (FLASH) requires precise focusing for advanced experiments.
• High-resolution spectroscopy, particularly vacuum-ultraviolet (VUV) Raman spectroscopy, demands tight aberration-free focal spots.

Purpose of the Study:

• To design and implement a Kirkpatrick-Baez (KB) refocusing mirror system for the PG1 beamline.
• To achieve a focal spot size of 4µm × 6µm full width at half-maximum (FWHM) on the sample.
• To ensure optimal performance and resolution of the VUV Raman spectrometer end-station.

Main Methods:

• Development of specialized fully motorized in-vacuum manipulators for KB mirror holders.
• Alignment of the KB optics using wavefront-sensing techniques.
• Analysis of ablative imprints to assess and minimize aberrations like astigmatism.

Main Results:

• Successful implementation of the KB refocusing mirror system at the FLASH PG1 beamline.
• Achieved tight aberration-free focusing down to 4µm × 6µm FWHM.
• Minimized aberrations, including astigmatism, to enhance spectral resolution.

Conclusions:

• The developed KB mirror system and alignment procedures effectively deliver the required microfocus spot size.
• The system enables unprecedented energy resolution for VUV spectroscopy at FLASH.
• This advancement supports high-resolution studies at soft X-ray/XUV free-electron laser facilities.