Direct Reconstruction of Terahertz-driven Subcycle Electron Emission Dynamics

TL;DR

This paper demonstrates a novel method to directly reconstruct subcycle electron emission dynamics driven by terahertz fields, revealing phase-dependent behaviors and enabling precise temporal characterization without pump-probe setups.

Contribution

It introduces a pump-probe-free technique for directly reconstructing electron emission profiles from energy spectra, validated by phase-resolved simulations.

Findings

Electron emission durations range from 73.0 to 81.0 fs with increasing field strength.

Spectral peaks scale linearly with THz field at zero CEP, indicating subcycle emission.

Emission current can be suppressed by up to 99.7% through phase control.

Abstract

While field-driven electron emission is theoretically understood down to the subcycle regime, its direct experimental temporal characterization using long-wavelength terahertz (THz) fields remains elusive. Here, by driving a graphite tip with phase-stable quasi-single-cycle THz pulses, we reveal distinct subcycle electron emission dynamics including: (1) At a carrier-envelope phase (CEP) zero, spectral peaks scale linearly with THz field strength, characteristic of subcycle emission; (2) At nearly opposite CEP, dominant deceleration fields generate stationary low-energy peaks. Crucially, we develop a pump-probe-free, direct reconstruction method extracting electron pulse profiles solely from measured energy spectra, obtaining durations from 73.0 to 81.0 fs as the field increases (191-290 kV/cm). Phase-resolved simulations further reveal a 72.8% modulation in the cutoff energy and a near-total (99.7%) suppression of the emission current. This work not only validates the field-emisssion theory under THz excitation but also establishes a general framework for the direct temporal characterization of subcycle electron emission, opening pathways for precise electron control in ultrafast electron sources and lightwave nanoelectronics.