Regensburg 2025 – scientific programme
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O: Fachverband Oberflächenphysik
O 10: Focus Session Ultrafast Electron Microscopy at the Space-Time Limit II
O 10.2: Talk
Monday, March 17, 2025, 15:30–15:45, H2
Spectrally resolved free electron-light coupling strength in a transition metal dichalcogenide — •Soufiane El kabil1, David Lerchenberger1, Niklas Müller1, Jonathan Weber1, Alexander Schröder1, and Sascha Schäfer1,2 — 1University of Regensburg, Regensburg, Germany — 2Regensburg Center for Ultrafast Nanoscopy, Regensburg, Germany
In ultrafast transmission electron microscopy (UTEM), combining precisely controlled free-electron beams with localized light fields enables the creation of intricate electronic states and the visualization of transient optical near-fields via PINEM [B. Barwick, et al. Nature 462.7275 (2009): 902-906]. However, optical nearfields in photonic structures typically exhibit a strong wavelength dependence, which has so far only been partially captured by PINEM approaches.
To address this, we use strongly chirped broadband light pulses to explore the spectrally resolved interaction between free electrons and light at the edge of a MoS2 thin film [N. Müller, et al. arXiv preprint arXiv:2405.12017(2024).]. As a fast electron traverses the optical field near the MoS2 flake, it absorbs or emits multiple photons, producing photon sidebands in its energy spectrum. By varying the electron-light delay at the sample, different spectral components of the near-field can be investigated. Numerical simulations reveal that the observed spectral and spatial modulations stem from interactions between incident and reflected light fields, as well as guided thin-film optical modes. Our results highlight the ability of PINEM to resolve the optical properties of semiconductors spatially and spectrally.
Keywords: ultrafast transmission electron microscopy (UTEM); PINEM; free electron-light coupling strength; optical properties of semiconductors; transition metal dichalcogenide (TMDC)