  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.
