Inertialess and Resonance Nonlinearity in Colloidal CdSe/ZnS Quantum Dots in the Case of Two-Photon Excitation of Excitons

The features of degenerate four-wave mixing by means of two-photon excitation of exciton transitions in a colloidal solution of CdSe/ZnS quantum dots (QDs) were revealed. This process was studied by means of dynamic Bragg gratings creation in colloidal QDs solution. The intensity of the generated pulses as a result of the degenerate four-wave interaction should be proportional to the cube of the incident pulses intensity. However, the 6th degree dependence and the quadratic dependence were experimentally measured for the first half and for the second half of the pulses in the train, correspondingly. To determine the features of the two-photon absorption the dependence of the intensity of the transmitted and self-diffracted pulses on the incident pulses intensity was measured. The experimental results can indicate a simultaneous effect on the transmission and refraction of the colloidal solution of QDs in the case of resonant two-photon excitation of the basic exciton transition as a non-inertial (classical) nonlinearity and resonance nonlinearity associated with a strong exciton absorption.