Strong optical nonlinearities of semiconductor quantum wires and dots

Picosecond laser saturation spectroscopy method has been applied to investigate nonlinear optical properties of semiconductor quantum wires and dots. Discrete bleaching bands have been observed in the time-resolved nonlinear transmission spectra of GaAs and CdSe quantum wires crystallized in crysotile asbestos nanotubes with an average diameter of 6 nm, in CdSe nanocrystals (quantum dots) in the glass matrix, in porous silicon, and in nanocrystals of CdS (CdS has been crystallized in a transparent molecular filter-mica with through empty channels of designed diameter). The induced increase of transmission at discrete frequencies has been attributed to the saturation of optical transitions between the energy levels of electrons and holes spatially confined within quasi-zero-dimensional and quasi-one-dimensional nanostructures and by the phase-space filling of excitons.