Nanosecond electron microscopes

Area of Science:

• Physics
• Materials Science
• Surface Science

Background:

• Advanced imaging techniques are crucial for understanding ultrafast material dynamics.
• Laser-matter interactions below the ablation threshold present unique challenges for observation.

Purpose of the Study:

• To develop and utilize high-speed electron microscopy for visualizing nanosecond and femtosecond laser-induced processes.
• To differentiate the material responses to nano- and femtosecond laser pulses.

Main Methods:

• Construction of transmission and photoelectron emission microscopes.
• Integration of electron optics, fast electronics, and pulsed lasers.
• Achieving a time resolution of several nanoseconds for dynamic event visualization.

Main Results:

• Successfully visualized laser-induced events in thin films and on surfaces with nanosecond resolution.
• Observed distinct material responses to nanosecond versus femtosecond laser pulses.
• Identified thermo/chemocapillary flow and chemical reactions for nanosecond pulses.
• Detected mechanical deformations and non-thermal electron emission for femtosecond pulses.

Conclusions:

• High-speed electron microscopy offers a unique capability to track fast laser-induced processes below the ablation threshold.
• The material response is highly dependent on the laser pulse duration (nanosecond vs. femtosecond).
• Different physical and chemical mechanisms govern the material behavior under different laser pulse regimes.