Biography:

Claus Ropers is a director at the Max Planck Institute for Multidisciplinary Sciences in Göttingen, Germany. He studied physics in Göttingen an Berkeley, California, and received his PhD in Berlin on studies plasmonic excitations in nanostructures (2007). Studying ultrafast carrier dynamics in graphite and graphene as a postdoc at the Max-Born Institute, he was appointed to an assistant professorship at the University of Göttingen in 2008, with promotions to associate (2011) and full professor (2013). In 2021, he joined the Max Planck Society, maintaining a part-time appointment at the University of Göttingen. His research group explores ultrafast imaging and diffraction using femtosecond electron and extreme-ultraviolet pulses. The groups' developments include ultrafast transmission electron microscopy (UTEM) based on laser-triggered field emitters, ultrafast low-energy electron diffraction (ULEED), and ultrafast high-harmonic nanoscopy of magnetization dynamics. Awards for his research include two ERC grants, the Ernst-Ruska-Prize, and the Gottfried Wilhelm Leibniz Prize.

LECTURE: "Coherent inelastic electron-light scattering"

The lecture will introduce basic principles and applications of quantum-coherent modulations of free-electron wavefunctions, including the notion of free-electron quantum walks, Photon-induced near-field electron microscopy (PINEM), and quantum-state tomography of temporally shaped electron beams.

TALK: "Probing electron-photon and electron-electron correlations in electron microscopy"

The talk will describe recent experiments studying elementary interactions of photons and electrons. A first set of experiments focuses on phase-matched electron-light scattering at integrated photonic microresonators [1,2]. We measure photons created in the cavity by spontaneous inelastic scattering of free electrons, in coincidence with those electrons having lost the corresponding photon energy. [2]. A second set of experiments reveals the Coulomb correlations of electrons produced by photoemission from a nanoscale field emitter. We observe characteristic spectral distributions of two-, three- and four-electron states, as well as pronounced energy and transverse momentum correlations arising from interparticle interaction [3].

References:

[1] "Integrated photonics enables continuous-beam electron phase modulation" J.-W. Henke, A. S. Raja, A. Feist, G. Huang, G. Arend, Y. Yang, J. Kappert, R. N. Wang, M. Möller, J. Pan, J. Liu, O. Kfir, C. Ropers and T. J. Kippenberg Nature 600, 653 (2021)

[2] "Cavity-mediated electron-photon pairs" A. Feist, G. Huang, G. Arend, Y. Yang, J.-W. Henke, A. S. Raja, F. J. Kappert, R. N. Wang, H. Lourenço-Martins, Z. Qiu, J. Liu, O. Kfir, T. J. Kippenberg, C. Ropers. Science 377, 777-780 (2022)

[3] "Coulomb-correlated electron number states in a transmission electron microscope beam" R. Haindl, A. Feist, T. Domröse, M. Möller, J. H. Gaida, S. V. Yalunin, C. Ropers. Nat. Phys., (appeared online, 2023).