Two-dimensional transition metal carbides/nitrides (MXenes) have attracted a lot of attention as optical materials owing to their unique electronic and optical features. In this paper, we demonstrated the nonlinear optical response of Ti₃C₂ MXene in the near infrared (NIR) regime at 1 and 1.3 µm. The nonlinear optical absorption behavior was systematically studied by the open/closed aperture (OA/CA) Z-scan techniques. Under a low excitation intensity, the saturable absorption dominated the optical nonlinear process, and the maximum effective nonlinear absorption coefficients β_eff were −0.59 cm/MW and −0.68 cm/MW at 1 and 1.3 µm, respectively. The nonlinear refractive index n₂ and the third-order susceptibility of Ti₃C₂ Mxene at 1 µm were −2.18 ×10⁻² cm²/GW and 3.65×10⁻³ esu, respectively. While with the excitation laser at 1.3 µm, the nonlinear refractive index n₂ was −1.64×10⁻² cm²/GW and the third-order susceptibility was 2.75×10⁻³ esu. With the increase of incident optical intensity, the two-photon absorption (TPA) process was observed, leading to the reverse absorption phenomenon. Our results confirmed that Ti₃C₂ MXene possessed intensity-depended nonlinear optical properties, which could be applied in various nonlinear optical devices.

中文翻译：

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层状 Ti3C2 MXene 在近红外区域的三阶非线性特性和反向吸收行为

由于其独特的电子和光学特性，二维过渡金属碳化物/氮化物（MXenes）作为光学材料引起了很多关注。在本文中，我们展示了 Ti ₃ C ₂ MXene 在近红外 (NIR) 范围内 1 和 1.3 µm的非线性光学响应。通过开/闭孔径 (OA/CA) Z 扫描技术系统地研究了非线性光吸收行为。在低激发强度下，可饱和吸收主导了光学非线性过程，最大有效非线性吸收系数β _eff在1和1.3 µm处分别为-0.59 cm/MW和-0.68 cm/MW。非线性折射率 n ₂和 Ti 的三阶磁化率₃ C ₂ Mxene在1μm处分别为-2.18×10 ^-2 cm ² /GW和3.65×10 ^-3 esu。而在1.3μm的激发激光下，非线性折射率n ₂为-1.64×10 ^-2 cm ² /GW，三阶磁化率为2.75×10 ^-3 esu。随着入射光强度的增加，观察到双光子吸收（TPA）过程，导致反向吸收现象。我们的结果证实，Ti ₃ C ₂ MXene 具有强度相关的非线性光学特性，可应用于各种非线性光学器件。