Strong-field above-threshold photoemission from sharp metal tips

TL;DR

This paper reports on energy-resolved electron emission from sharp metal tips under low-energy laser pulses, revealing above-threshold photoemission up to nine photons and strong-field effects influenced by surface field enhancement.

Contribution

It provides the first detailed measurements of above-threshold photoemission from metal tips at low intensities, highlighting the role of surface field enhancement in strong-field phenomena.

Findings

Observation of up to 9-photon above-threshold photoemission

Suppression of the lowest order peak at high intensities

Linear peak shifting with intensity indicating strong-field effects

Abstract

We present energy-resolved measurements of electron emission from sharp metal tips driven with low energy pulses from a few-cycle laser oscillator. We observe above-threshold photoemission with a photon order of up to 9. At a laser intensity of 2*10^11 W/cm^2 suppression of the lowest order peak occurs, indicating the onset of strong-field effects. We also observe peak shifting linearly with intensity with a slope of around -1.8eV / (10^12 W/cm^2). We attribute the magnitude of the laser field effects to field enhancement taking place at the tip's surface.