COHERENT THZ PLASMONS IN GAAS - TRANSITION FROM PURE PLASMONS TO COUPLED PLASMON-PHONON MODES

We report on the observation of coherent THz plasmons in GaAs using th e femtosecond time-resolved pump-probe technique. Tile samples are GaA s/AlGaAs modulation doped single heterostructures with a depletion fie ld below the PD-channel in the intrinsic GaAs substrate. For the first time, several coherent oscillations !up to five full periods) are cle arly visible in the frequency range of 1.5 to 5 THz. The observed osci llation frequencies increase with Increasing carrier densities. Our ex perimental data are in good agreement with theoretical Ensemble-Monte- Carlo simulations.