Pulsed Laser Deposition Of TiO₂-based Composite Films And Optical Properties

In this work,TiO₂ films and nano-composite films containing Au particles embedded in TiO₂ matrices were fabricated using pulsed laser deposition technique(PLD).The structure and nonlinear optical properties of the films were investigated.The nonlinear optical properties were measured by Z-scan method using femtosecond laser.And the films show large optical nonlinear responses.The main results are listed as follows,(1) The effects of the substrate temperature,oxygen pressure and laser fluences on the crystal structure of TiO₂ films were studied.For the first time,c-axes oriented anatase TiO₂ films and(110) oriented rutile TiO₂ films were fabricated on Si(100),respectively. The results of X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR) and Raman spectra show that the prepared films have good crystal structure.(2) The nonlinear optical properties of the anatase and rutile TiO₂ films were investigated by z-scan method using amplified femtosecond laser and seed femtosecond laser.When amplified femtosecond laser was used,the nonlinear optical refractive indexes of the anatase films and the rutile film were measured to be 6.32×10^-17m²/W and -2.7×10^-17m²/W,the nonlinear refractive indexis were -6.2×10^-11m/Wå’Œ-2.6×10^-10m/W, respectively.When the seed femtosecond laser was used,the nonlinear optical absorption coefficients were negative,but the nonlinear refractive indexes were positive.(3) Au:TiO₂ composite films were fabricated using PLD method.The crystal structure of the films was determined by XRD.The linear optical properties of the films were analyzed by transmission spectra.The results show that the position of surface plasmon resonance(SPR) peaks of the composite films changes to longer wavelength with the increasing of the annealing temperature and Au concentration.The nonlinear optical properties of the films were investigated by z-scan method using amplified femtosecond laser and seed femtosecond laser.When the amplified femtosecond laser was used,the nonlinear optical absorption coefficients and refractive indexes of the films were negative. The nonlinear optical responses increase with the increasing of the Au concentration. When the seed femtosecond laser was used,the nonlinear refractive indexes were positive, the nonlinear absorption coefficients of the films before annealing treatment change from negative to positive with the increasing of Au concentration.However,after annealing the nonlinear absorption coefficients were negative for all composite films.(4) Multilayer Au/TiO₂ composite films were fabricated by PLD.The transmission spectra were measured.The results show that the SPR peak position of Au/TiO₂ films change to longer wavelength with the increasing of the Au concentration.The nonlinear optical absorption coefficients and refractive indexes were determined to be negative by z-scan method using amplified femtosecond laser.(5) Composite films consisting of periodic gold nanoparticle arrays coated with TiO₂ were fabricated using PLD method.The effects of the Au particle size and the TiO₂ matrix on the peak position of the films were investigated.The results show the peak position show red shift with the increasing of the Au particle size.