Near field optical spectroscopy of confined excitons

Two novel approaches for mapping the microscopic carrier dynamics in semico nductor nanostructures in real space and time are discussed. Combining quas i two-color femtosecond pump-probe spectroscopy and near-field microscopy, the temporal evolution of the nonlinear change in reflectivity of a single GaAs quantum wire is imaged with a time resolution of 200 fs and a spatial resolution of 200 nm. The experiments evidence the ultrafast relaxation of carriers into a quantum wire at room temperature and carrier transport alon g the wire axis. The second approach is based on an optical marker techniqu e using a novel electronically coupled wire-dot sample grown on (311)A GaAs substrates. First low temperature near-field spectra reveal the interestin g proper ties of this nanostructure.