Time-Resolved Investigation of Coherently Controlled Electric Currents at a Metal Surface
J. Güdde,
M. Rohleder,
T. Meier,*
S. W. Koch,
U. Höfer
Studies of current dynamics in solids have been hindered by insufficiently brief trigger signals and electronic detection speeds. By combining a coherent control scheme with photoelectron spectroscopy, we generated and detected lateral electron currents at a metal surface on a femtosecond time scale with a contact-free experimental setup. We used coherent optical excitation at the light frequencies 
a and a/2 to induce the current, whose direction was controlled by the relative phase between the phase-locked laser excitation pulses. Time- and angle-resolved photoelectron spectroscopy afforded a direct image of the momentum distribution of the excited electrons as a function of time. For the first (n = 1) image-potential state of Cu(100), we found a decay time of 10 femtoseconds, attributable to electron scattering with steps and surface defects.
Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, Renthof 5, D-35032 Marburg, Germany.
* Present address: Department Physik, Universität Paderborn, Warburger Str. 100, D-33098 Paderborn, Germany.
To whom correspondence should be addressed. E-mail: hoefer{at}physik.uni-marburg.de
