Molecular Physics seminar

Ultrafast Electron Microscopy – Pump Probe TEM

by Jonas Weissenrieder (Materials and Nano Physics, KTH Royal Institute of Technology)

FD41 ()


The presentation will introduce ultrafast electron microscopy (UEM), a technique facilitating microscopic imaging, diffraction, and spectroscopy at picosecond timescales. UEM can be described as pump probe transmission electron microscopy (TEM) where the probing electron bunches are generated by a femtosecond UV laser pulse while a synchronized laser pulse excites a change in the sample. Some selected results from the UEM community will be reviewed and both possibilities and limitations of the technique discussed. Experimental challenges in sample preparation, especially energy dissipation, will be presented together with some solutions and strategies to remedy such problems. I will also show the design and some preliminary time resolved results from the recently constructed UEM at KTH. Time and energy resolutions of the KTH microscope have been characterized using photoinduced near field electron microscopy (PINEM) where the probe electrons interact with a plasmonic field generated by the exciting laser in a conductive sample. The dynamics of the electron pulses are compared to simulation of the electron gun in the relevant 3D geometry, showing the benefits for UEM of tailored cathode designs. Preliminary time resolved electron diffraction results from a photoexcited charge density wave phase transition in TaSe2 will be shown as well as time resolved Lorentz microscopy of demagnetization and domain boundary dynamics in permalloy (Ni80Fe20).