National Synchrotron Light Source Symposium

"Femtosecond Electron Diffraction: Probing Structural Dynamics on the Fundamental Timescale"

Presented by Jianming Cao, Florida State University

Tuesday, September 5, 2006, 10:30 am — Seminar Room, Bldg. 725


Atomic motions on the timescale of single vibrational period (~100 fs) govern the genesis and evolution of new phases in solids, the kinetic pathways of chemical reactions, and the processes of biological functions. To understand these structural dynamics at the atomic level requires monitoring the motions of atoms with milli-ångström and sub-ps spatial-temporal resolution. In this lecture, I will talk about our efforts in developing such an ultrafast structure probe, femtosecond electron diffraction (FED), and present some results of our recent studies of laser-induced ultrafast structural dynamics in thin metal films. With the sub milli-ångström and sub-ps spatial-temporal resolution of FED, we are able to directly monitor in real time both coherent and thermal atomic motions in the film, which provides new insights into the ultrafast thermal expansion dynamics. In particular, we find that the electronic thermal expansion contributes significantly to drive the coherent lattice motions. Using FED, we also developed a new method of measuring electronic Grüneisen constant γe via differentiating the lattice and electronic contributions to the thermal expansion in time domain. This new approach opens the way to determining the γe values in many magnetic materials with low Curie temperatures, where the accurate measurement of γe is not amenable with other traditional techniques.

Hosted by: Xijie Wang

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