The soft X-ray and XUV split-and-delay unit at beamlines FL23/24 at FLASH2.

Area of Science:

• Physics
• Laser Science
• Materials Science

Background:

• Time-resolved experiments are crucial for understanding ultrafast phenomena.
• Existing methods for soft X-ray and extreme ultraviolet (XUV) studies have limitations in temporal resolution and spectral range.
• The Free-electron LASer in Hamburg (FLASH) provides high-intensity coherent radiation for advanced experiments.

Purpose of the Study:

• To develop and implement a split-and-delay unit for time-resolved experiments at FLASH.
• To enable soft X-ray pump/soft X-ray probe (SXR/SXP) experiments with high temporal resolution.
• To characterize the performance of the split-and-delay unit, including transmission and timing jitter.

Main Methods:

• Geometric wavefront splitting using a beam-splitting mirror with Ni and Pt coatings.
• Utilizing grazing incidence angles (1.8° for variable path, 1.3° for fixed path) to optimize reflectivity across the spectral range up to 1800 eV.
• Implementing a delay line for pump-probe experiments with a range of -5 ps to +18 ps.

Main Results:

• Achieved high transmission values for both Ni and Pt coatings across different energy ranges.
• Demonstrated soft X-ray pump/soft X-ray probe capabilities with a nominal time resolution of 66 attoseconds (as) and timing jitter of 121 ± 2 as.
• Measured an averaged coherence time of 1.75 fs at 8 nm for FLASH2, even with reduced coherence.

Conclusions:

• The developed split-and-delay unit is a robust tool for advanced time-resolved SXR/XUV experiments.
• The unit's performance characteristics enable high-precision studies of ultrafast dynamics.
• This technology significantly enhances the experimental capabilities at FLASH for fundamental research.