A multi-MHz single-shot data acquisition scheme with high dynamic range: pump-probe X-ray experiments at synchrotrons

Area of Science:

• * Physics
• * Chemistry
• * Materials Science

Background:

• * Advanced synchrotron radiation sources provide high-repetition rate X-ray pulses, enabling faster experiments.
• * Laser-X-ray pump-probe techniques offer insights into molecular dynamics with high temporal resolution.
• * Previous methods were limited by data acquisition speed, hindering the full exploitation of high-repetition rate sources.

Purpose of the Study:

• * To present the technical implementation of a multi-MHz data acquisition scheme for laser-X-ray pump-probe experiments.
• * To enable experiments with pulse-limited temporal resolution (100 ps) at high X-ray repetition rates.
• * To achieve high sensitivity and signal-to-noise ratios for studying molecular systems in liquid solutions.

Main Methods:

• * Utilized a synchronized 3.9 MHz laser excitation source and 7.8 MHz X-ray pulses in 60-bunch mode at PETRA III beamline P01.
• * Recorded total X-ray fluorescence yield (TFY) from liquid samples using silicon avalanche photodiode detectors (APDs).
• * Employed a digitizer card for 0.5 ns sampling with 12-bit resolution, processing signals to determine TFY per X-ray pulse and averaging over ~10^7 pulses.

Main Results:

• * Achieved sensitivity down to the shot-noise limit.
• * Demonstrated signal-to-noise ratios approaching 1000 within seconds of collection time per data point.
• * The system exhibits a dynamic range of 100 photons/pulse, limited primarily by the APD technology.

Conclusions:

• * The developed multi-MHz data acquisition scheme effectively supports high-repetition rate laser-X-ray pump-probe experiments.
• * The technique allows for rapid and sensitive measurements of molecular dynamics in liquid solutions.
• * This advancement opens new possibilities for time-resolved studies at modern synchrotron facilities.