Tuned intensity-dependent refractive index n2 and two-photon absorption in oxide glasses: Role of non-bridging oxygen bonds in optical nonlinearity

Several nonlinear glass parameters such as second-order refractive index, n2, third-order susceptibility χ(3), the imaginary part of χ(3) and two-photon absorption coefficient are calculated for five different oxide glass systems. The glasses exhibit considerable optical nonlinearities. It has been found that the decrease in band gap energy and Fermi energy increases the glass nonlinear optical properties. Glasses contain either chromium oxide, magnesium or barium oxide exhibit considerable nonlinearity comparing with titanium-containing glasses. The origin of this nonlinearity and the ability to tune it has been discussed based on the glass linear refractive indices, nonbridging oxygen bonds, hyperpolarizability of modifier cations and on the rule of these cations on the creation of nonbridging oxygen bonds.