Near-field imaging of one-dimensional excitons delocalized over mesoscopic distances

Near-field optical spectroscopy is used to investigate the effects of disorder in the optical processes in semiconductor quantum wires. We observe photoluminescence emissions from extended, delocalized excitons at low temperatures ~5 K! and low excitation densities. Combining high spectral and spatial resolution, we isolate homogeneous emission lines from excitons delocalized over distances up to 600 nm in the fundamental state. The energies of the emissions are consistent with different quantum spatial confinements along the wire axis. Unlike the photoluminescence originating from localized excitons, these emission lines show a high degree of polarization along the axis of the wire.