Dynamic analysis of multiple-photon optical processes in semiconductor quantum dots

Semiconductor quantum dots (QDs) have been gaining much attention because of their outstanding properties for multiple-photon microscopy applications. By solving nonperturbatively the time-dependent Schrodinger equation, it has been shown that the large number of energy states densely compacted in both the conduction and valence bands of the QD greatly enhance the inter-band and intra-band optical couplings between two energy states induced by multiple photons from ultra-fast and ultra-intense lasers. The multiphoton absorption processes are further enhanced by many energy relaxation processes in commonly used semiconductors, which are generally represented by the relaxation energy in the order of tens of meV. Numerical calculation of multiphoton processes in QDs agrees with experimental demonstration. After proper designing, QDs can be activated by infrared radiation to emit radiation in the visible optical regime (up-conversion) for bioimaging applications.