Tunable Nanosecond and Femtosecond Nonlinear Optical Properties of C–N–S-Doped TiO2 Nanoparticles

Abstract

Third-order nonlinear optical (NLO) properties of undoped and C–N–S doped TiO2 nanoparticles (NPs) were investigated using the Z-scan technique in the nanosecond (ns) and femtosecond (fs) regimes. Undoped TiO2 NPs exhibited reverse saturable absorption (RSA) behavior with both ns and fs laser pulse excitation, whereas C–N–S-doped TiO2 NPs demonstrated switch over from RSA to saturable absorption (RSA → SA) behavior with fs excitation. Our detailed NLO studies have clearly demonstrated the tunable nonlinear absorption behavior of C–N–S-doped TiO2 NPs. Such versatile tunability is important for various practical applications. The interesting nonlinear absorption (NLA) properties of these NPs are attributed to the interplay between ground and excited state absorption of the free carriers. The results obtained with ns laser excitation demonstrated that the nonlinear absorption coefficient (β) and nonlinear refractive index (n2) for these materials varied with input irradiance, thus indicating the possibility ...