222 research outputs found
Relaxation of Femtosecond Non-equilibrium Electrons in a Metallic Sample
A model calculation is given for the energy relaxation of a non-equilibrium
distribution of hot electrons prepared in a metallic sample that has been
subjected to homogeneous photo-excitation by a femtosecond laser pulse. The
model assumes that the delta pulse photoexcitation creates two interpenetrating
electronic subsystems, initially comprising a dilute energy-wise higher-lying
non-degenerate hot electron subsystem, and a relatively dense, lower-lying
electron subsystem which is degenerate. In the femtosecond time regime the
relaxation process is taken to be dominated by the electron-(multi) phonon
interaction, resulting in a quasi-continuous electron energy loss to the phonon
bath. The kinetic model is given for this time regime, beacuse in this time
regime the usual Two Temperature model is not applicable. The Two Temperature
model assumes that the hot electrons and phonons are in their respective
equilibrium states (Fermi and Bose) but at a different temperatures. One uses
the Bloch-Boltzmann-Peierls transport formula to calculate the energy transfer
rate. In the present Kinetic model a novel physical feature of slowing down
(due to Fermionic blocking of interaction phase space) of electron-phonon
relaxation mechanism near the Fermi energy of degenerate electronic subsystem
is considered. This leads to a peaking of the calculated hot electron
distribution at the Fermi energy. This feature, as well as the entire evolution
of the hot electron distribution, may be time-resolved by a femto-second
pump-probe study.Comment: 5 pages,4 figure
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