Nonlinear optical response of a single self-assembled InGaAs quantum dot: A femtojoule pump-probe experiment

A single InGaAsGaAs quantum dot is addressed in a two-color femtosecond transmission experiment in the optical near-field of a nanometer-scale shadow mask. After resonant excitation of the wetting layer beneath the nanoisland, we detect transmission changes of the quantum dot with narrow band femtojoule probe pulses. We find bleaching signals in the order of 10-5 that arise from individual interband transitions. Moreover, the nonlinear optical response reveals a picosecond dynamics associated with carrier relaxation in the quantum dot. As a result, we have developed an ultrafast optical tool for both manipulation and readout of a single self-assembled quantum dot.