Direct observation of space charge dynamics by picosecond low-energy electron scatteringC. Cirelli1, 2, M. Hengsberger1, A. Dolocan1, H. Over2, J. Osterwalder1 and T. Greber1
1 Physik-Institut, Universität Zürich-Irchel - Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
2 Physikalisch-Chemisches Institut, Justus Liebig Universität - Heinrich-Buff-Ring 58, D-35392 Giessen, Germany, EU
received 8 October 2008; accepted in final form 5 December 2008; published January 2009
published online 19 January 2009
The transient electric field governing the dynamics of space charge is investigated by time- and energy-resolved low-energy electron scattering. The space charge above a copper target is produced by high-intensity femtosecond laser pulses. The pump-probe experiment has a measured temporal resolution of better than 35 ps at 55 eV probe electron energy. The probe electron acceleration due to space charge is reproduced within a 3-dimensional non-relativistic model, which determines an effective number of electrons in the space charge cloud and its initial diameter. Comparison of the simulations with the experiments indicates a Coulomb explosion, which is consistent with transients in the order of 1 ns, the terminal kinetic energy of the cloud and the thermoemission currents predicted by the Richardson-Dushman formula.
78.47.jc - Time resolved spectroscopy ( > 1 psec).
87.64.Bx - Electron, neutron and X-ray diffraction and scattering.
79.40.+z - Thermionic emission.
© EPLA 2009