Power and composition dependent non linear optical switching of TiO2-SiO2 nano composites

Linear as well as nonlinear absorption of TiO₂-SiO₂ nanocomposites prepared by sol gel process has been reported. To investigate the nonlinear properties, Z Scan technique was employed with 532 nm as the excitation wavelength followed by the calculation of the nonlinear optical constants. Z-scan experiments showed that when the excitation energy increased, the nonlinear absorption of the nanocomposites changed from reverse-saturable absorption to saturable absorption and then again back to reverse saturable absorption. Such a changeover in the sign of the nonlinearity is related to the interplay of exciton bleach and optical limiting mechanisms. The observed nonlinear absorption is found to be due to two photon absorption. The enhancement of the third-order nonlinearity in the composites can be due to the concentration of exciton oscillator strength.