'Ultrafast microscopy down to the scale of atoms

Measuring the interactions between light and matter over the smallest possible length- and timescales has been a long-sought goal across condensed matter physics and optics. By exploiting evanescent fields confined to miniscule objects, near-field microscopy can access light-matter interaction on nanometre length scales and with femtosecond time resolution [1]. In this talk, I will first discuss several recent applications of terahertz near-field microscopy for sampling ultrafast dynamics in quantum materials. Then, I will discuss a fundamentally new paradigm for ultrafast microscopy which exploits strong atomic nonlinearities hidden deep within optical near-fields. In doing so, simultaneous atomic-scale spatial resolution and subcycle time resolution become possible for the first time [2]. This emergent nonlinear response originates from electromagnetic radiation emitted by tunnelling currents flowing in response to the THz electric field [3,4]. This fundamentally new imaging mechanism - near-field optical tunnelling emission (NOTE) - provides the first subcycle videography of atomic-scale quantum dynamics.

[1] M. Plankl et al., “Subcycle contact-free nanoscopy of ultrafast interlayer transport in atomically thin heterostructures”, Nat. Photonics, 15, 594 (2021).
[2] T. Siday et al., “All-optical subcycle microscopy on atomic length scales”, Nature, 629, 329 (2024).
[3] T. L. Cocker et al., “An ultrafast terahertz scanning tunnelling microscope”, Nat. Photonics, 7, 620 (2013).
[4] T. L. Cocker et al., “Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging”, Nature, 539, 263 (2016).