Femtosecond near-field optical spectroscopy of implantation patterned semiconductors

We have developed a femtosecond-resolved near-field scanning optical microscope, using a diffraction-limited pump and near-field probe configuration, which allows us to measure carrier dynamics with a spatial resolution of ∼150 nm and a time resolution of ∼250 fs. This instrument is used for near-field degenerate pump–probe studies of carrier dynamics in GaAs/AlGaAs single quantum well samples locally patterned by focused-ion-beam (FIB) implantation. We find that lateral carrier diffusion across the nanometer-scale FIB pattern plays a significant role in the decay of the excited carriers.