The ultrafast transmission electron microscope (UTEM) in our lab has recently shown how it can be used to image spatiotemporal dynamics. The concept is that the interaction between free electrons and an excitation in the sample can change the free electron energy. Then, we use an energy filtering on the post-interaction electron, to reconstruct the image of the excitation we are interest in. Thus, the energy filtering creates a single image of the excitation. This technique is called energy-filtered transmission electron microscopy (EFTEM). The temporal dynamics is found using our pump-probe technique. A pump laser pump reaches the sample and generates the excitation of interest, and the free electron can probe the sample at different time delays compared to the excitation pump.
Spatiotemporal imaging of 2D polariton wavepackets
In a recent paper, we shown how this technique can be used to image the spatiotemporal dynamics of hyperbolic phonon-polariton wavepackets inside isotopically pure hBN (11B) flakes when the pump was in the mid-infrared regime. A video that explaines the whole experiment is presented below:
In this experiment, not only we have measured for the first time a wavepacket of light that is confined to 2D materials, but we also showed how the wavepackets can change their group velocity during their propagation and split into two different wavepackets.
First measurement of an optical wavepacket in 2D materials
phonon-polariton wavepacket splitting
|•||Y. Kurman†, R. Dahan†, H. Herzig Shenfux, K. Wang, M. Yannai, Y. Adiv, O. Reinhardt, L. H. G. Tizei, S. Y. Woo, J. Li, J. H. Edgar, M. Kociak, F. H. L. Koppens, and I. Kaminer, Spatiotemporal imaging of 2D polariton wavepacket dynamics using free electrons, Science 372, 1181-1186 (2021) (Supplementary materials) “A short YouTube movie that explains the measurement concept“|
|•||K. Wang, R. Dahan, M. Shentcis, Y. Kauffmann, A. Ben- Hayun, O. Reinhardt, S. Tsesses, I. Kaminer, Coherent Interaction between Free Electrons and Cavity Photons, Nature 582, 50 (2020) (Supplementary materials) § Selected for Research Highlights in Nature Reviews Physics and featured in phys.org and in various Israeli media outlets|