Time-resolved pump-probe experiments at the LCLS.

Area of Science:

• * Ultrafast science
• * X-ray science
• * Molecular dynamics

Background:

• * Time-resolved X-ray/optical pump-probe experiments require precise synchronization between optical lasers and X-ray free-electron lasers.
• * Achieving sub-picosecond timing resolution is critical for studying ultrafast phenomena in matter.

Purpose of the Study:

• * To perform the first time-resolved X-ray/optical pump-probe experiments at the Linac Coherent Light Source (LCLS).
• * To develop and apply methods for synchronizing an ultrafast optical laser to a linac-based X-ray laser.
• * To accurately characterize the timing jitter between the optical and X-ray pulses.

Main Methods:

• * Employed a combination of feedback methods and post-analysis binning techniques for synchronization.
• * Utilized transient molecular nitrogen alignment revival features in time-dependent X-ray-induced fragmentation spectra to determine temporal overlap.
• * Applied strong-field dissociation of X-ray generated quasi-bound molecular dications to establish residual timing jitter.

Main Results:

• * Successfully synchronized an ultrafast optical laser with the LCLS X-ray pulses.
• * Resolved transient molecular nitrogen alignment revival features, enabling precise temporal overlap determination.
• * Established the relative arrival time distribution of the Ti:Sapphire laser and X-ray pulses with a standard deviation of approximately 120 fs.
• * Identified the laser oscillator's locking to the accelerator's RF as the dominant jitter source.

Conclusions:

• * The developed synchronization techniques enabled the first time-resolved X-ray/optical pump-probe experiments at LCLS.
• * The timing jitter was characterized, revealing a standard deviation of ~120 fs.
• * Technical improvements, specifically addressing laser oscillator locking, could reduce jitter to below 50 fs, paving the way for more precise experiments.