Third harmonic and sum-frequency generation in ZnO quantum dots

Within the framework of the density matrix approach we investigate the third harmonic generation (THG) and sum frequency generation (SFG) associated with the intersublevel transitions in the conduction band of a singly charged ZnO quantum dot (QD). With three optical fields incident on the dot, we obtain the third order nonlinear susceptibility resulting in the THG and the SFG processes. As compared to the bulk enhanced value of the third order nonlinear susceptibility is obtained through the electric dipole interactions of the pump fields with the electron in the QD. Results are obtained for the THG and SFG in the ZnO QD embedded in the HfO2, Al2O3, AlN, and SiO2 matrices. The results show that the dot size and the surrounding matrix significantly influence the third order nonlinear susceptibility, which is found to be relatively higher for the QD embedded in the high-dielectric constant HfO2 matrix as compared to the other matrices.