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.

1. INTRODUCTION

Nanostructured materials possess unique physical and chemical properties as a result of their small size. These properties differ largely from those of the corresponding single molecules and bulk materials [1]. materials have attracted a great deal of attention, largely because they have a wide range of applications in many technologies, such as solar cell, [2],[3] photocatalysis [4] and photonic bandgap materials[5],[6]. Modulation of the refractive index of optical thin films has been the subject of research for various optical applications, such as waveguides in biosensing techniques, optical fibers and photonic crystals. [7]. By mixing of two different materials with high and low refractive indices to yield composite films with an intermediate index. As a consequence, the refractive index will depend on their composition and phase transition of the composite film.