Third-order nonlinear optical properties of TiO₂ films

Anatase TiO₂ films were fabricated on fused quartz by pulsed laser deposition (PLD) technique and the single-phase anatase films were obtained under the optimal conditions. The X-ray diffraction and atomic force microscope were used to investigate the structure and surface characters of the film. The third-order optical nonlinearities of the films were measured by Z-scan technique using a femtosecond laser (50fs) of 800 nm. From the transmission spectra, the optical band-gap and linear refractive index of the TiO₂ film are determined to be 3.18 eV and 2.1, respectively. The nonlinear absorption coefficient and nonlinear refractive index are determined to be -6.2 × 10^-11 m/W and -6.32 × 10^-17 m²/W, respectively.The real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ are determined to be -7.1 × 10^-11 esu and -4.42 × 10^-12 esu, respectively. And the following figure of merit T=βλ/n₂ is calculated to be 0.8 for the film, indicating that the anatase TiO₂ films have great potential applications to nonlinear optical devices.