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Time-Resolved Investigation of Coherently Controlled Electric Currents at a Metal Surface

currentscheme

The animation illustrates the optical generation of electric current pulses as short as 50 femtoseconds (1 femtosecond (fs) = 10-15 s) and their time-resolved detection with photoelectron spectroscopy. Ultrashort, phase-locked laser pulses (drawn in yellow and blue) generate an electron current at a metal surface whose direction and magnitude is controlled by the relative phase ΔΦ between the corresponding oscillating light fields. The excited electrons that carry the current are emitted from the sample by a third laser pulse (drawn in red) via the photoelectric effect. The current is monitored by directly measuring the velocity distribution of the charge carriers. The electrons typically travel at a speed of 1 Å/fs or 100 km/s parallel to the surface. In the animation most of the electrons excited with ΔΦ= 90° initially move to the right. Due to scattering processes with defects the velocity distribution of the electrons gets symmetric on the femtosecond time scale and the current decays. In the experiment, this ultrafast decay is time-resolved by applying a pump-probe scheme. For that purpose, the sequence of current generation and detection is repeated with different time delays between the excitation and photoemission pulses. The simplified illustration shows the equivalent measurement of one-time excitation and continuous probing.

Reference

J. Güdde, M. Rohleder, T. Meier, S.W. Koch, U. Höfer,
Time-Resolved investigation of coherently controlled electric currents at a metal surface,
Science 318, 1287 (2007)


Zuletzt aktualisiert: 27.05.2015 · armbrusn

 
 
 
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