Faster Than Femtoseconds

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Science  21 Apr 2006:
Vol. 312, Issue 5772, pp. 333d
DOI: 10.1126/science.312.5772.333d

The time resolution of chemical dynamics studies has generally been limited by the duration of laser pulses used as probes. Pulse durations now approach 1 femtosecond (fs), but some molecular events occur on even more rapid time scales. Baker et al. (p. 424, published online 2 March; see the Perspective by Bucksbaum) show that an 8-fs laser pulse can be used to observe nuclear dynamics of H2 and methane after ionization with 0.1-fs (10−16 s) resolution. The technique relies on the electrons being ejected from the molecule by the laser pulse with a spread of velocities, which in turn leads to a spread, or chirp, in frequency of the photons released upon electron-ion recombination. The emitted photon frequency acts as a clock that is more precise than the excitation pulse.

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