The propagation of light in the epsilon-near-zero (ENZ) region of materials exhibits intriguing linear and nonlinear optical phenomenon that have been extensively exploited for a plethora of applications. Here, we show that the optical properties as well as the ENZ wavelength of magnetron-sputtered indium tin oxide (ITO) thin films could be judiciously engineered. The measurement of nonlinear optical properties reveals that the control of deposition conditions allows for the tuning of absorptive optical nonlinearity between saturable absorption and reverse saturable absorption. The ENZ wavelength for the ITO film is deduced as around 1553 nm. We obtain the highest third-order nonlinear absorption coefficient and imaginary part of third-order nonlinear susceptibility for the ITO thin film through Z-scan method as −50.56 cm/GW and ∼38 × 10−14 e.s.u. at 1050 nm, and −64.50 cm/GW and ∼45 × 10−14 e.s.u. at 1550 nm, respectively. We demonstrate further that the strong saturable absorption of the ITO thin film enables Q-switched pulse laser generation in ∼1050 and ∼1550 nm regions with tunable repetition rates and pulse energies. The present results suggest the great application potential of the ITO thin film in the field of nonlinear optical devices.

中文翻译：

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用于ε-近零区域光开关的铟锡氧化物的可调谐光学非线性

光在材料的近零 (ENZ) 区域中的传播表现出有趣的线性和非线性光学现象，这些现象已被广泛用于大量应用。在这里，我们表明可以明智地设计磁控溅射氧化铟锡 (ITO) 薄膜的光学特性和 ENZ 波长。非线性光学特性的测量表明，沉积条件的控制允许调节可饱和吸收和反向可饱和吸收之间的吸收光学非线性。ITO 薄膜的 ENZ 波长推断为 1553 nm 左右。我们通过Z扫描方法获得了ITO薄膜的最高三阶非线性吸收系数和三阶非线性磁化率的虚部为-50.56 cm / GW和~38×10-14esu 在 1050 nm，-64.50 cm/GW 和 ∼45 × 10-14esu 在 1550 nm，分别。我们进一步证明，ITO 薄膜的强可饱和吸收能够在~1050 和~1550 nm 区域内产生具有可调重复率和脉冲能量的 Q 开关脉冲激光。目前的结果表明ITO薄膜在非线性光学器件领域的巨大应用潜力。