Temporal characterization of femtosecond electron pulses inside ultrafast scanning electron microscope

TL;DR

This paper introduces an all-optical in situ method to measure femtosecond electron pulse durations in an ultrafast scanning electron microscope, enabling precise characterization across various energies.

Contribution

The work presents a novel optical technique for directly measuring electron pulse durations inside an ultrafast SEM, with detailed analysis of how photon energy affects pulse length.

Findings

Achieved electron pulse durations from 0.5 ps to 2.7 ps across 5.5-30 keV energies.

Reduced photon energy of photoemission pulses decreases initial energy spread and shortens electron pulses.

Demonstrated in situ measurement capability for femtosecond electron pulses in an ultrafast SEM.

Abstract

In this work, we present the implementation of all-optical method for directly measuring electron pulse duration in an ultrafast scanning electron microscope. Our approach is based on the interaction of electrons with the ponderomotive potential of an optical standing wave and provides a precise in situ technique to characterize femtosecond electron pulses at the interaction region across a wide range of electron energies (1-30 keV). By using single-photon photoemission of electrons by ultraviolet femtosecond laser pulses from a Schottky emitter we achieve electron pulse durations ranging from 0.5 ps at 30 keV to 2.7 ps at 5.5 keV under optimal conditions where Coulomb interactions are negligible. Additionally, we demonstrate that reducing the photon energy of the femtosecond pulses used for photoemission from 4.8 eV (257.5 nm) to 2.4 eV (515 nm) decreases the initial energy spread of emitted electrons, leading to significantly shorter pulse durations, particularly at lower electron energies.