Time-resolved ion imaging at free-electron lasers using TimepixCam.

Area of Science:

• Atomic and Molecular Physics
• Optical Sciences
• Instrumentation

Background:

• Molecular photoionization experiments often require precise timing and detection of multiple fragment ions.
• Velocity-map imaging is a key technique for analyzing fragment ion momentum distributions.
• Existing detector technologies can limit data acquisition rates and comparability in complex experiments.

Purpose of the Study:

• To introduce and evaluate the TimepixCam, a novel fast optical-imaging camera, for molecular photoionization studies.
• To demonstrate the advantages of TimepixCam in velocity-map imaging experiments at a free-electron laser.
• To enhance data acquisition efficiency and experimental comparability, particularly for pump-probe studies.

Main Methods:

• Utilized TimepixCam, a 256x256 pixel CMOS camera with 20 ns timing resolution, for ion hit detection and time-stamping.
• Applied the velocity-map imaging technique in conjunction with a free-electron laser source.
• Recorded ion momentum images for all fragment ions simultaneously without detector gating.

Main Results:

• TimepixCam enables simultaneous recording of all fragment ion momentum images.
• Achieved 20 ns timing resolution for ion hits, significantly improving data collection.
• Overcame limitations in pump-probe experiments caused by free-electron laser timing and pulse energy drifts.
• Facilitated potential application of ion-ion covariance and coincidence techniques.

Conclusions:

• TimepixCam offers a significant advancement for molecular photoionization experiments using velocity-map imaging.
• The camera enhances data throughput and experimental reliability, crucial for free-electron laser applications.
• Simultaneous fragment ion detection simplifies complex experiments and opens new avenues for correlation studies.