Lau Kuen Yao, Yang Yuting, Zhao Di, Liu Xiaofeng, Qiu Jianrong
College of Optical Science and Engineering and State Key Lab of Modern Optical Instrumentation, Zhejiang University, 310027, Hangzhou, China.
School of Materials Science and Engineering, Zhejiang University, 310027, Hangzhou, China.
Nanophotonics. 2022 Aug 9;11(18):4209-4219. doi: 10.1515/nanoph-2022-0306. eCollection 2022 Sep.
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 e.s.u. at 1050 nm, and -64.50 cm/GW and ∼45 × 10 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.
光在材料的近零介电常数（ENZ）区域中的传播呈现出有趣的线性和非线性光学现象，这些现象已被广泛应用于众多领域。在此，我们表明磁控溅射氧化铟锡（ITO）薄膜的光学性质以及ENZ波长可以经过审慎设计。非线性光学性质的测量结果表明，通过控制沉积条件，可以在可饱和吸收和反饱和吸收之间调节吸收性光学非线性。推导得出ITO薄膜的ENZ波长约为1553纳米。通过Z扫描方法，我们在1050纳米处获得ITO薄膜的最高三阶非线性吸收系数和三阶非线性极化率的虚部，分别为-50.56厘米/吉瓦和约38×10静电单位，在1550纳米处分别为-64.50厘米/吉瓦和约45×10静电单位。我们进一步证明，ITO薄膜的强可饱和吸收能够在约1050和约1550纳米区域产生调Q脉冲激光，且重复频率和脉冲能量可调。目前的结果表明ITO薄膜在非线性光学器件领域具有巨大的应用潜力。
