Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 84: Focus Session: Structural Dynamics in Nanoscale Materials Probed by Ultrashort Electron Pulses

O 84.6: Topical Talk

Donnerstag, 19. März 2015, 16:30–17:00, MA 005

Exploring the Spatial and Temporal Resolution Limits of Ultrafast Electron Microscopy — •David J. Flannigan, Dayne A. Plemmons, Daniel R. Cremons, and David T. Valley — University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN, 55455, USA

In ultrafast electron microscopy (UEM), the capabilities of transmission electron microscopy are extended into the femtosecond temporal domain. The operating principle of UEM requires spatiotemporal overlap of the photon pulse and electron packet at the specimen; at time zero, significant photon absorption by the freely-propagating electrons can occur. Overlap at the specimen suggests this phenomenon can be used to measure the response function and the electron packet properties. In this talk, I will discuss considerations for isolating the inherent artifacts of the highly non-linear near-field interactions from the actual packet characteristics. Further, I will discuss how temporal cross-sections of peaks in the electron-energy spectra corresponding to high-order transitions are expected to exhibit the true temporal behavior of the electron packets. In general, the exceedingly small portion of the pump laser pulse capable of initiating such transitions results in temporal widths converging to the electron packet duration. Additionally, population of quantized virtual states occurring for an electron beam focused on a nanostructure suggests that the resulting energy distribution may produce discrete chromatic aberrations arising from the velocity dependence of the Lorentz force. I will discuss the prospect for detecting such phenomena in bright-field images.