Dynamics of coherent plasmon-phonon coupled modes in GaAs using ultrashort laser pulses

Dynamical properties of coherently excited plasmon-phonon systems have been studied by a reflection-type pump-probe technique. Samples used in this study are n-type GaAs. In the present work, using 20 fs ultra short laser pulses, we have observed coherent oscillations of the upper mode (L+) as well as the lower mode (L-) in plasmon-phonon systems. The line shape and the peak frequency of the L- and L+ bands vary strongly on the photoexcited carrier densities. The dependence of the mode frequencies on carrier density is in agreement with predicted behavior. (C) 1998 Elsevier Science B.V. All rights reserved.