Laser-induced Field Emission from Tungsten Tip: Optical Control of Emission Sites and Emission Process

TL;DR

This study demonstrates optical control of laser-induced electron emission from a tungsten tip, achieving site-specific, ultrafast pulsed emission with detailed understanding of emission mechanisms and dependencies on experimental parameters.

Contribution

It provides a comprehensive analysis of how laser polarization and tip orientation influence emission patterns, introducing a method for site-selective ultrafast electron sources.

Findings

Emission patterns depend on laser polarization and tip orientation.

Two-photon photo-excitation dominates at high tip voltage and low laser power.

Photoemission from the tip shank increases with laser power.

Abstract

Field-emission patterns from a clean tungsten tip apex induced by femtosecond laser pulses have been investigated. Strongly asymmetric field-emission intensity distributions are observed depending on three parameters: (1) the polarization of the light, (2) the azimuthal and (3) the polar orientation of the tip apex relative to the laser incidence direction. In effect, we have realized an ultrafast pulsed field-emission source with site selectivity of a few tens of nanometers. Simulations of local fields on the tip apex and of electron emission patterns based on photo-excited nonequilibrium electron distributions explain our observations quantitatively. Electron emission processes are found to depend on laser power and tip voltage. At relatively low laser power and high tip voltage, field-emission after two-photon photo-excitation is the dominant process. At relatively low laser power and low tip voltage, photoemission processes are dominant. As the laser power increases, photoemission from the tip shank becomes noticeable.