Ultrafast electron diffraction and microscopy are capable of revealing the pathways
of atomic motion during structural processes. Their temporal resolution has so far been limited to several hundred femtoseconds. We aim to advance these techniques gradually into the few-femtosecond (and possibly even sub-femtosecond) regime of electron charge density motions. Single electron pulses, which we demonstrated in the 1st fp, are an important advance in this direction. Ultrafast single-electron diffraction constitutes an ideal approach for visualising electronic motion on the atomic and nano-scale. Our concept is based on three pillars: (i) a few-cycle multicolour laser system operating at repetition rates of 0.1-1 MHz (developed in Project A.1.1), combined dc-microwave acceleration for electron compression and sub-femtosecond resolution electron metrology via streaking / deflection using waveform-controlled few-cycle light. This work is also likely to benefit from the nano-tips developed in Project B.3.5 which may improve the emittance and coherence of the electron source.
We propose to image, via deflectometry, the oscillating electron density in nano-plasmonic structures driven initially with low-frequency, far-infrared radiation produced in Project A.1.1. By shortening the single-electron pulse duration towards 10 fs and below we will reduce the size and increase the frequency of plasmonic oscillations used for validation of the metrology. The envisioned advances in our sub-MHz-rate single-electron source will lead us to imaging atomic-scale charge oscillations induced resonantly or non-resonantly in nanometre semiconductor or dielectric films at ever higher infrared frequencies, approaching eventually the optical regime. Femtosecond single-electron diffraction will be used for imaging the charge carrier dynamics at the nano- to atomic-scale in the lightwave-nano-electronic devices developed and scrutinised in Projects B.3.2 and B.3.3.
In addition, the Angstrom spatial resolution combined with eventually few-femtosecond temporal resolution will also be exploited for recording snapshots of charge density motion during molecular dynamics involving multiple coherently excited states and conical intersections, in collaboration with Projects B.2.1 and B.2.2. On the long run, single-electron diffraction may be able to visualise the sub-fs motion of electron charge
in nano-structures as well as molecular systems.