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MM: Fachverband Metall- und Materialphysik

MM 5: Topical Session Interface Dominated Phenomena - Poster

MM 5.10: Poster

Dienstag, 28. September 2021, 10:00–12:45, P

Broadband coupling of fast electrons with high-Q whispering gallery mode resonators — •Niklas Müller, Vincent Hock, Christopher Rathje, Nora Bach, Holger Koch, and Sascha Schäfer — Institute of Physics, University of Oldenburg, 26129 Oldenburg, Germany

The inelastic interaction of fast electrons with spatially confined intense light fields has recently enabled new techniques in ultrafast transmission electron microscopy (UTEM), enabling the coherent control of free-electron states. Advanced quantum control scenarios, including electron-light entanglement and non-trivial electron/photon counting statistics, become accessible if non-classical light states are applied. However, to mitigate the reduced coupling strength when considering few-photon-states, novel concepts for coupling electrons to high-Q optical resonators are required. Here, we demonstrate the excitation of high-Q whispering gallery modes in a silica microfiber taper in a transmission electron microscope by relativistic electrons (200 keV) passing close to the fiber surface. The evanescent electric field of the passing electron induces a femtosecond electric polarization in the silica, which can be decomposed into optical whispering gallery modes (WGM). The dtected coherent cathodoluminescence spectra consist of octave-spanning frequency combs with narrow-bandwidth peaks. By probing the WGM resonances for different distances from the taper apex, we demonstrate that the peaks within the comb exhibit a frequency spacing inversely scaling with the local fiber circumference. Q-factors up to 700 a measured, depending on the local taper angle.