Ultrafast electron diffraction

Ultrafast Electron Diffraction (UED) is a pump-probe experimental method based on the combination of optical pump-probe spectroscopy and electron diffraction. UED provides information on the dynamical changes of the structure of materials. In the UED technique, a femtosecond (fs) laser optical pulse excites (pumps) a sample into an excited, usually non-equilibrium, state. The pump pulse may induce chemical, electronic or structural transitions. After a finite time interval, a fs electron pulse is incident upon the sample. The electron pulse undergoes diffraction as a result of interacting with the sample. The diffraction signal is, subsequently, detected by an electron counting instrument such as a CCD camera. Specifically, after the electron pulse diffracts from the sample, the scattered electrons will form a diffraction pattern (image) on a CCD camera. This pattern contains structural information about the sample. By adjusting the time difference between the arrival (at the sample) of the pump and probe beams, one can obtain a series of diffraction patterns as a function of the various time differences. The diffraction data series can be concatenated in order to produces a motion picture of the changes that occurred in the data. UED can provide a wealth of dynamics on charge carriers, atoms, and molecules.

Electron Pulse Production The electron pulses are produced by the process of photoemission in which a fs optical pulse is directed toward a photocathode. If the incident laser pulse has an appropriate energy, electrons will be ejected from the photocathode through a process known as photoemission.

Sources

• Srinivasan, Ramesh; Lobastov, Vladimir A.; Ruan, Chong-Yu; Zewail, Ahmed H. (2003). "Ultrafast Electron Diffraction (UED): A New Development for the 4D Determination of Transient Molecular Structures". Helvetica Chimica Acta. 86 (6): 1761. doi:10.1002/hlca.200390147.

@article{Sciaini_2011, doi = {10.1088/0034-4885/74/9/096101}, url = {https://doi.org/10.1088%2F0034-4885%2F74%2F9%2F096101}, year = 2011, month = {aug}, publisher = {{IOP} Publishing}, volume = {74}, number = {9}, pages = {096101}, author = {Germ{\'{a}}n Sciaini and R J Dwayne Miller}, title = {Femtosecond electron diffraction: heralding the era of atomically resolved dynamics}, journal = {Reports on Progress in Physics},

}