Blue-shifting of coherent plasmon radiation due to Landau damping
Restricting the wave vector of coherent plasmons excited by ultrashort laser pulses results in a frequency blue-shift of the emitted THz radiation, consistent with the onset of Landau damping.
Coherent plasmons in n-doped GaAs
Femtosecond laser excitation of bulk $n$-doped GaAs leads to coherent plasmon excitations that emit intense submillimeter wave radiation. We investigated the underlying plasmon dynamics in time-resolved experiments on the emitted THz radiation. The results show that THz pulses are emitted due to the coherent oscillation of the extrinsic electron plasma in the bulk. The plasmon excitations are started by single-sided screening of the surface depletion field after photoexcitation. Temperature-dependent measurements indicate that the plasmon damping is due to phonon scattering.
Diffusion and drift in terahertz emission at GaAs surfaces
We study terahertz (THz) emission from GaAs as a function of photon energy and electric field. THz radiation arises from transport of photogenerated charge in an electric field and by hot carrier diffusion (the photo-Dember effect). These mechanisms can be separated by experiments in which either the electric field or the kinetic energy of the carriers is varied. For electric fields E∼4 kV/cm, we find that the electric field controls THz emission for carrier temperatures kBTC⩽0.1 eV, while hot-carrier diffusion dominates for kBTC≈1 eV. Both mechanisms contribute at intermediate fields and carrier temperatures. Our results are consistent with estimates of the relative magnitudes of these two effects.