A study of Linear and Nonlinear Changes and optical absorption coefficient of Quantum dots

Important advances in both epitaxial growth and laser technologies have created a growing interest in the linear and nonlinear optical properties of quantum dots (QDs). In this study, the nonlinear optical properties, including the linear and nonlinear changes in the refractive index and optical absorption, have been studied, with the electric field effect. The electronic structures of the disk-like and spherical QDs are calculated using the effective-mass and dipole approximation, for the two different confining potentials; an infinitely deep and a parabolic. The nonlinear optical coefficients are written within the density matrix formalism. The results show that the total change in the refractive index increases with increasing QD size but the total absorption coefficients decrease. The peaks are blue-shifted for decreasing QD size. The nonlinear optical properties increase as the strength of the applied electric field and the optical intensity increase. Comparison of QD types shows that the refractive index changes and the absorption coefficients in the disk-like QD are lower than those in the spherical QD. Also the infinitely deep confining potential results in higher confinement effects and optical response compared to those observed in the parabolic potential case.