Coherent plasmon-phonon oscillations in a GaAs schottky barrier sample

We have observed coherent plasmon–phonon oscillations in a biased GaAs–Au Schottky barrier sample excited by intense fs laser pulses using time resolved Second Harmonic Generation. The results are compared with Monte-Carlo simulations. To account for the observed dependence of the frequency on the excitation density it was necessary to separate the electric field in two components: one due to the space charge and the other following from the lattice polarization. In this way a coupling between the plasmon and the LO phonons is obtained, which resulted in a nearly perfect description of the experimentally observed frequencies.