Origin of optical nonlinearity for PbO, $TiO2,$ $K2O,$ and $SiO2$ optical glasses Available to Purchase

The nonlinear optical properties for the PbO, $TiO2,$ $K2O,$ and $SiO2$ system have been measured by the $Z$-scan method. The magnitude and sign of the nonlinear refractive index $n2$ were determined, as was the negative sign, which indicated a self-defocusing optical nonlinearity. Two optical absorption bands at 540 and 660 nm, respectively, are observed in the optical absorption spectra. The sources of the absorption bands are attributed to the $3d$-shell electronic transitions of $Ti3+$ ions from the ground state to the excited states. The origin of the negative nonlinear refractive index was the contribution of resonant electronic transition processes, which can cancel the positive nonresonant refractive index that mainly resulted from the hyperpolarizabilities of the Pb–O and Ti–O pairs.