Ultrafast scanning probe microscope

• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: Funded in 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544202205

It is the aim of this proposal to implement an ultrafast scanning probe microscope that probes electromagnetic fields dynamics of (individual) nanostructures with ultra-high spatial resolution, ideally at the atomic level, and ultra-high temporal resolution in the sub-femtosecond range. This addresses a central, previously unsolved problem in nano-optics. Recently, the applicants have developed a new approach based on phase-resolved detection of coherent light scattering from scanning probe tips over a broad spectral range. Fourier analysis of these data provides the temporal structure of the electromagnetic field emitted by the coupled tip-sample system with (sub)-femtosecond resolution. Detection with a very fast camera allows us to sense changes in the field structure when varying the tip-sample distance, enabling the reconstruction of the three-dimensional structure of the optical near-field. With this, we can precisely characterize the important tip-sample interaction, which is crucial for a quantitative theoretical description of spectroscopic signals. In simple terms, the developed technique functions as an ultrafast nano-oscilloscope. So far, this approach has only been tested by us at room temperature and under ambient conditions, limiting the spatial resolution to a few nanometers. To successfully use the method for characterizing individual nanostructures, it is essential to conduct measurements under controlled environmental conditions and at low temperatures. We expect that this will also significantly improve the achievable spatial resolution. To perform the corresponding experiments, a cryogenic scanning probe microscope is requested. It will allow for measuring coherent light scattering and scanning tunneling luminescence spectra on the same nanostructure, characterizing both the optical excitation and emission of the nanostructure. This new approach will be utilized in cooperation with the Schneider Research Group to study individual single-photon emitters in transition metal dichalcogenide monolayers. The new microscope will also provide a novel approach towards spatially resolved spectroscopy of strongly coupled exciton-plasmon systems, contributing to the understanding of the roles of bright and dark exciton states and the modification of excitonic transport in such systems. Finally, we expect that the newly developed nano-oscilloscope will enable time-resolved, nonlinear optical experiments on individual nanostructures, allowing the tracking of the dynamics of non-equilibrium excitations.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Ultraschnelles Rastersondenmikroskop
• Instrumentation Group: 5091 Rasterkraft-Mikroskope
• Applicant Institution: Carl von Ossietzky Universität Oldenburg
• Leader: Professor Christoph Lienau, Ph.D.