Third-order optical nonlinearity of indium-doped rutile TiO2 thin films

Rutile TiO2 and Ti0.9In0.1O2 thin films were fabricated using a pulsed laser deposition method. We employed the optical transmission spectra to reveal the good transparency of the films in the visible spectral range of 330 to 900 nm. The absorption edge of the Ti0.9In0.1O2 film is blue-shifted compared with that of undoped TiO2 film. The third-order optical nonlinearity of the films was investigated by using a z-scan method with a pulse laser operating at 532 nm with a duration of 55 ps. The results show that the Ti0.9In0.1O2 and TiO2 films exhibit nonlinear saturable absorption and negative nonlinear refraction. The doping of In ions does not change the nonlinear optical absorption of the TiO2 film significantly. However, the nonlinear refractive index of Ti0.9In0.1O2 film is about two times larger than that of undoped TiO2 film. The local electron-pinned defect-dipoles and widening bandgap in the Ti0.9In0.1O2 film can be used to explain the observed results.