Direct Reconstruction of Terahertz-Driven Subcycle Electron Emission Dynamics

Area of Science:

• Physics
• Ultrafast Science
• Materials Science

Background:

• Field-driven electron emission is theoretically understood in the subcycle regime.
• Direct experimental temporal characterization using long-wavelength terahertz (THz) fields has been elusive.

Purpose of the Study:

• To experimentally characterize subcycle electron emission dynamics driven by THz fields.
• To develop a pump-probe-free method for direct temporal characterization of electron emission.
• To validate field emission theory under THz excitation.

Main Methods:

• Driving a graphite tip with phase-stable quasi-single-cycle THz pulses.
• Analyzing spectral peaks and energy spectra of emitted electrons.
• Developing a direct reconstruction method for electron pulse profiles.
• Performing phase-resolved simulations.

Main Results:

• Observed distinct subcycle electron emission dynamics, including linear scaling of spectral peaks with THz field strength at CEP zero and stationary low-energy peaks at opposite CEP.
• Successfully extracted electron pulse profiles with durations of 73.0–81.0 fs.
• Simulations showed significant modulation in cutoff energy (72.8%) and suppression of emission current (99.7%).

Conclusions:

• Validated field emission theory under THz excitation.
• Established a general framework for direct temporal characterization of subcycle electron emission.
• Opened pathways for precise electron control in ultrafast electron sources and lightwave nanoelectronics.