We report the experimental observation of giant dispersive and absorptive optical nonlinearities in direct current magnetron sputtered as-grown and annealed $ {{\rm TiO}_2} $ thin films. The $ {{\rm TiO}_2} $ film was deposited in a mixture of argon and oxygen. The as-grown film and the film annealed below 250°C demonstrated amorphous behavior having particle size variation in the range of 15–20 nm, while the films annealed above temperature $ \ge 300^\circ{\rm C} $ exhibited crystalline structure with larger particle size (50–80 nm). The enhancement in optical nonlinearity in amorphous films can be attributed to small particle sizes, while in crystalline thin films, the enhancement in optical nonlinearity is attributed to phonon-assisted resonant transitions. The films are characterized by the x-ray diffraction technique, atomic force microscopy, UV–visible spectroscopy, and Raman spectroscopy for their structural properties, morphology, bandgap, and presence of phonon modes, respectively. The intensity-dependent nonlinear optical properties of the films are analyzed by using the Z-scan technique.

中文翻译：

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TiO ₂薄膜中的巨大色散和吸收光学非线性

我们报告了直流磁控溅射成膜并退火的{{{rm TiO} _2} $薄膜中的巨大色散和吸收光学非线性的实验观察。将$ {{\ rm TiO} _2} $薄膜沉积在氩气和氧气的混合物中。刚生长的薄膜和在250°C以下退火的薄膜表现出无定形行为，其粒径在15–20 nm范围内变化，而在温度以上退火的薄膜$ \ ge 300 ^ \ circ {\ rm C} $表现出较大粒径（50-80 nm）的晶体结构。非晶膜中光学非线性的增强可归因于小粒径，而在结晶薄膜中光学非线性的增强归因于声子辅助的共振跃迁。薄膜的结构特性，形态，带隙和声子模态分别通过X射线衍射技术，原子力显微镜，紫外可见光谱和拉曼光谱进行表征。通过使用Z扫描技术分析薄膜的强度相关的非线性光学性质。