Photodiode-based time zero determination for ultrafast electron microscopy

Area of Science:

• Ultrafast electron microscopy
• Femtosecond laser physics
• Materials science

Background:

• Pump-probe experiments in ultrafast electron microscopy (UEM) demand precise temporal overlap between excitation (pump) and probing (probe) pulses.
• Accurate determination of time zero (t0) is critical for resolving ultrafast dynamics in materials.
• Existing methods for t0 determination can be complex or costly.

Purpose of the Study:

• To present a cost-effective and user-friendly photodiode-based method for measuring time zero in UEM.
• To enable precise temporal alignment of single-electron pulses with femtosecond laser pulses.
• To establish a foundation for achieving micrometer and picosecond spatiotemporal resolution.

Main Methods:

• Development of a photodiode integrated into a sample holder for UEM.
• Utilizing the photodiode to detect the temporal overlap between electron and laser pulses.
• Characterization of the temporal resolution of the developed alignment method.

Main Results:

• A photodiode-based alignment device was successfully implemented for time zero measurements.
• The initial device achieved a temporal resolution of 24 picoseconds (ps).
• The photodiode's design was identified as the limiting factor for temporal resolution.

Conclusions:

• The photodiode method offers a practical approach for achieving time zero alignment in UEM.
• Future improvements using photodiodes with lower capacitance will enhance temporal and spatial resolution.
• This technique paves the way for advanced spatiotemporal investigations in UEM.