Sol–Gel Preparation and Third-Order Nonlinear Optical Properties of TiO2 Thin Films

Rutile and anatase thin films have been prepared by the sol–gel method using Ti(OC3H7i)4. Third-order nonlinear optical properties of both TiO2 thin films have been investigated by the third-harmonic generation (THG) method and the effect of the polymorph of TiO2 on the third-order nonlinear optical susceptibility, χ(3), has been examined. The measured χ(3) values of rutile and anatase thin films were 1.4 × 10−12 and 9.7 × 10−13 esu, respectively. The χ(3) values corrected for the porosity of the film were 4.0 × 10−12 (rutile) and 2.4 × 10−12 esu (anatase), which are about 100 times as high as that of SiO2 glass used as standard sample (2.8 × 10−14 esu). The measured and corrected χ(3) values were discussed in comparision with those calculated on the basis of several models.