Extreme lightwave electron field emission from a nanotip

• Published in: Physical review research 2021-02, Vol.3 (1), p.013137, Article 013137
• Main Authors: Matte, Dominique, Chamanara, Nima, Gingras, Lauren, de Cotret, Laurent P. René, Britt, Tristan L., Siwick, Bradley J., Cooke, David G.
• Format: Article
• Language: English
• ISSN: 2643-1564; 2643-1564
• DOI: 10.1103/PhysRevResearch.3.013137

We report on subcycle terahertz light-field emission of electrons from tungsten nanotips under extreme conditions corresponding to a Keldysh parameter γ_{K}≈10^{−4}. Local peak THz fields up to 40 GV/m are achieved at the apex of an illuminated nanotip, causing subcycle cold-field electron emission and acceleration in the quasistatic field. By simultaneous measurement of the electron bunch charge and energy distribution, we perform a quantitative test of quasistatic Fowler-Nordheim tunneling theory under field conditions that completely suppress the tunnel barrier. Very high bunch charges of ∼10^{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. Application of this theory under such extreme THz field conditions predicts a single-shot electron energy distribution with a spectral purity reaching 10^{−4}. THz field-induced reshaping and sharpening of the nanotip is observed, reducing the tip radius from 120 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.