Femtosecond single- to few-electron point-projection microscopy for nanoscale dynamic imaging

TL;DR

This paper demonstrates femtosecond single-electron point projection microscopy with 120 fs temporal and 100 nm spatial resolution, enabling real-space imaging of ultrafast charge dynamics at the nanoscale.

Contribution

First implementation of femtosecond single-electron point projection microscopy in a laser-pump fs-e-probe setup with high temporal and spatial resolution.

Findings

Achieved 120 fs temporal resolution in electron microscopy.

Demonstrated imaging of charge distributions on a nanoscale metal tip.

Potential for sub-femtosecond to attosecond imaging applications.

Abstract

Femtosecond electron microscopy produces real-space images of matter in a series of ultrafast snapshots. Pulses of electrons self-disperse under space-charge broadening, so without compression, the ideal operation mode is a single electron per pulse. Here, we demonstrate for the first time femtosecond single-electron point projection microscopy (fs-ePPM) in a laser-pump fs-e-probe configuration. The electrons have an energy of only 150 eV and take tens of picoseconds to propagate to the object under study. Nonetheless, we achieve a temporal resolution with a standard deviation of 120 fs, combined with a spatial resolution of 100 nm, applied to a localized region of charge at the apex of a nanoscale metal tip induced by 30 fs 800 nm laser pulses at 50 kHz. These observations demonstrate real-space imaging of reversible processes such as tracking charge distributions is feasible whilst maintaining femtosecond resolution. Our findings could find application as a characterization method, which, depending on geometry could resolve tens of femtoseconds and tens of nanometres. Dynamically imaging electric and magnetic fields and charge distributions on sub-micron length scales opens new avenues of ultrafast dynamics. Furthermore, through the use of active compression, such pulses are an ideal seed for few-femtosecond to attosecond imaging applications which will access sub-optical cycle processes in nanoplasmonics.