Ultrafast scanning electron microscope applied for studying the interaction between free electrons and optical near-fields of periodic nanostructures

TL;DR

This paper presents an ultrafast scanning electron microscope setup that investigates inelastic electron scattering at optical near-fields of nanostructures, achieving femtosecond resolution and demonstrating controlled electron energy gain.

Contribution

The work introduces a novel ultrafast SEM setup with femtosecond resolution for studying electron near-field interactions, including techniques to control interaction distance and resonance conditions.

Findings

Electron pulse duration as low as 410 fs was achieved.

Interaction distance was increased via pulse-front-tilt of the laser.

Electron energy gain up to 3.8 keV was demonstrated.

Abstract

In this paper we describe an ultrafast scanning electron microscope setup developed for the research of inelastic scattering of electrons at optical near-fields of periodic dielectric nanostructures. Electron emission from the Schottky cathode is controlled by ultraviolet femtosecond laser pulses. The electron pulse duration at the interaction site is characterized via cross-correlation of the electrons with an infrared laser pulse that excites a synchronous periodic near-field on the surface of a silicon nanostructure. The lower limit of 410 fs is found in the regime of a single electron per pulse. The role of pulse broadening due to Coulomb interaction in multielectron pulses is investigated. The setup is used to demonstrate an increase of the interaction distance between the electrons and the optical near-fields by introducing a pulse-front-tilt to the infrared laser beam. Further we show the dependence of the final electron spectra on the resonance condition between the phase velocity of the optical near-field and the electron propagation velocity. The resonance is controlled by adjusting the initial electron energy/velocity and by introducing a linear chirp to the structure period allowing to increase the final electron energy gain up to a demonstrated 3.8 keV.