The prominent third-order nonlinear optical properties of WTe2 films are studied through the Z-scan technique using a femtosecond pulsed laser at 1030 nm. Open-aperture (OA) and closed-aperture (CA) Z-scan measurements are performed at different intensities to investigate the nonlinear absorption and refraction properties of WTe2 films. OA Z-scan results show that WTe2 films always hold a saturable absorption characteristic without transition to reverse saturable absorption. Further, a large nonlinear absorption coefficient β is determined to be −3.37×103 cm/GW by fitting the OA Z-scan curve at the peak intensity of 15.603 GW/cm2. In addition, through the slow saturation absorption model, the ground state absorption cross section, excited state absorption cross section, and absorber’s density were found to be 1.4938×10−16 cm2, 1.2536×10−16 cm2, and 6.2396×1020 cm−3, respectively. CA Z-scan results exhibit a classic peak–valley shape of the CA Z-scan signal, which reveals a self-defocusing optical effect of WTe2 films under the measured environment. Furthermore, a considerable nonlinear refractive index value n2 can be obtained at −1.629×10−2 cm2/GW. Ultimately, the values of the real and imaginary parts of the third-order nonlinear susceptibility of WTe2 are roughly estimated to be −5.93×10−9 and −1.01×10−8 esu with the help of first-principles calculations. WTe2 possesses sizeable third-order nonlinear coefficients compared with other materials, which suggests that it has great potential to improve performance in nonlinear optical devices.

中文翻译：

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脉冲激光沉积合成的WTe2薄膜的三阶非线性光学特性

使用 1030 nm 的飞秒脉冲激光，通过 Z 扫描技术研究了 WTe2 薄膜突出的三阶非线性光学特性。在不同强度下进行开放孔径 (OA) 和封闭孔径 (CA) Z 扫描测量，以研究 WTe2 薄膜的非线性吸收和折射特性。OA Z 扫描结果表明，WTe2 薄膜始终保持饱和吸收特性，而不会转变为反向饱和吸收。此外，通过在峰值强度 15.603 GW/cm2 处拟合 OA Z 扫描曲线，确定大的非线性吸收系数 β 为 -3.37×103 cm/GW。此外，通过慢饱和吸收模型，发现基态吸收截面、激发态吸收截面和吸收体密度分别为1.4938×10−16 cm2、1.2536×10−16 cm2、和 6.2396×1020 cm−3，分别。CA Z 扫描结果显示了 CA Z 扫描信号的经典峰谷形状，这揭示了 WTe2 薄膜在测量环境下的自散焦光学效应。此外，可以在-1.629×10-2 cm2/GW 处获得相当大的非线性折射率值n2。最终，在第一性原理计算的帮助下，WTe2的三阶非线性磁化率的实部和虚部的值粗略估计为-5.93×10-9和-1.01×10-8 esu。与其他材料相比，WTe2 具有相当大的三阶非线性系数，这表明它具有提高非线性光学器件性能的巨大潜力。这揭示了 WTe2 薄膜在测量环境下的自散焦光学效应。此外，可以在-1.629×10-2 cm2/GW 处获得相当大的非线性折射率值n2。最终，在第一性原理计算的帮助下，WTe2的三阶非线性磁化率的实部和虚部的值粗略估计为-5.93×10-9和-1.01×10-8 esu。与其他材料相比，WTe2 具有相当大的三阶非线性系数，这表明它具有提高非线性光学器件性能的巨大潜力。这揭示了 WTe2 薄膜在测量环境下的自散焦光学效应。此外，可以在-1.629×10-2 cm2/GW 处获得相当大的非线性折射率值n2。最终，在第一性原理计算的帮助下，WTe2的三阶非线性磁化率的实部和虚部的值粗略估计为-5.93×10-9和-1.01×10-8 esu。与其他材料相比，WTe2 具有相当大的三阶非线性系数，这表明它具有提高非线性光学器件性能的巨大潜力。WTe2的三阶非线性磁化率的实部和虚部的值在第一性原理计算的帮助下粗略估计为-5.93×10-9和-1.01×10-8 esu。与其他材料相比，WTe2 具有相当大的三阶非线性系数，这表明它具有提高非线性光学器件性能的巨大潜力。WTe2的三阶非线性磁化率的实部和虚部的值在第一性原理计算的帮助下粗略估计为-5.93×10-9和-1.01×10-8 esu。与其他材料相比，WTe2 具有相当大的三阶非线性系数，这表明它具有提高非线性光学器件性能的巨大潜力。