Extreme Lightwave Electron Field Emission from a Nanotip

TL;DR

This paper demonstrates extreme-field terahertz electron emission from tungsten nanotips, achieving high charge and energy, confirming Fowler-Nordheim tunnelling theory under intense fields, and observing tip reshaping, with implications for ultrafast electron sources.

Contribution

It provides the first quantitative analysis of electron emission at such extreme THz fields, confirming theoretical models and demonstrating tip reshaping effects.

Findings

Achieved local peak THz fields up to 40 GV/m at nanotip apex.

Observed high electron bunch charges of about 10^6 electrons per pulse.

Confirmed Fowler-Nordheim tunnelling theory under extreme field conditions.

Abstract

We report on sub-cycle terahertz light-field emission of electrons from tungsten nanotips under extreme conditions corresponding to a Keldysh parameter $\gamma_K\approx10^{-4}$. Local peak THz fields up to 40~GV/m are achieved at the apex of an illuminated nanotip, causing sub-cycle cold-field electron emission and acceleration in the quasi-static field. By simultaneous measurement of the electron bunch charge and energy distribution, we perform a quantitative test of quasi-static Fowler-Nordheim tunnelling theory under field conditions that completely suppress the tunnel barrier. Very high bunch charges of $\sim10^6$ electrons/pulse are observed, reaching maximum energies of 3.5~keV after acceleration in the local field. The energy distribution and emission current show good agreement with Fowler-Nordheim theory even in this extreme field regime. Extending this model to the single-shot regime under these conditions predicts peak electron distributions with a spectral purity of $10^{-4}$. THz field-induced reshaping and sharpening of the nanotip is observed, reducing the tip radius from 120~nm to 35~nm over roughly $10^9$ THz shots. These results indicate THz-driven nanotips in the extreme field limit are promising electron sources for ultrafast electron diffraction and microscopy.