GENERATION AND RELAXATION OF COHERENT MAJORITY PLASMONS

We report on the time-resolved study of the dynamics of coherent plasm on-phonon modes in n-doped GaAs at different doping levels. The measur ements show that the initially thermalized background majority plasma participates in the coherent plasmon-phonon oscillation and that the o bserved frequency is determined by the total electron density includin g both the background doping and the optical excitation. The dephasing of the coupled plasmon-phonon oscillation is found to be slower (i) a s the relative contribution of the optical excitation to the total car rier density decreases and (ii) as the frequency approaches that of th e transverse-optical phonon resonance.