Quantization energy mapping of single V-groove GaAs quantum wires by femtosecond near-field optics

We demonstrate that femtosecond pump–probe spectroscopy in the optical near field is well suited to study the intrinsic properties of single V-groove GaAs quantum wires. Temporally and spatially resolved experiments show that the shape of near-field pump–probe traces sensitively depends on the detuning between the laser photon energy and the lowest exciton resonance of a quantum wire. This detuning dependence allows one to map the quantization energy fluctuations along a single quantum wire with 200 nm spatial resolution. We measure fluctuations of about 12 meV over 2 μm wire length, resulting from wire thickness variations of 1 ML.