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Science  22 Apr 2011:
Vol. 332, Issue 6028, pp. 399
DOI: 10.1126/science.332.6028.399-a

The firing of the starting pistol sets the runners out of their blocks and hurtling down the race-track, and the race is often over in a blink of an eye. In the process of photoionization, photons with the right energy impinging on an atom will release an electron and leave behind a positively charged ion. Unlike the runners all lined up in a row, electrons are packed into atoms in a certain order, filling up different energy levels, generally the lowest first. Klünder et al. use an interferometric technique based on a frequency comb to study the dynamics of the photoionization process with electrons emitted from different energy levels in argon gas, specifically the 3s2 and 3p6 shells. With the capability of taking snapshots of the process at attosecond resolution, they show that there is a time delay between emissions of electrons from the different shells. Moreover, they also show that the timing of the electron emissions from a particular shell is dependent on the energy of the photons. The time resolution afforded by this and related spectroscopic techniques is providing insights into the ultrafast processes occurring within atoms that were once too rapid to see.

Phys. Rev. Lett. 106, 143002 (2011).

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