title: Femtosecond few- to single-electron point-projection microscopy for nanoscale dynamic imaging.
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 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 114 fs (equivalent to a full-width at half-maximum of 269 ± 40 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.
authors.forename: A R
authors.initials: AR
authors.lastname: Bainbridge
authors.affiliation: Department of Physics, College of Science, Swansea University , Singleton Park, Swansea SA2 8PP, United Kingdom.
authors.forename: C W
authors.initials: CW
authors.lastname: Barlow Myers
authors.affiliation: Department of Physics, College of Science, Swansea University , Singleton Park, Swansea SA2 8PP, United Kingdom.
authors.forename: W A
authors.initials: WA
authors.lastname: Bryan