Neupane Tikaram, Poudyal Uma, Tabibi Bagher, Kim Wan-Joong, Seo Felix Jaetae
Department of Chemistry and Physics, The University of North Carolina at Pembroke, Pembroke, NC 28372, USA.
Advanced Center for Laser Science and Spectroscopy, Department of Physics, Hampton University, Hampton, VA 23668, USA.
Materials (Basel). 2023 Oct 12;16(20):6664. doi: 10.3390/ma16206664.
The cubic nonlinearity of a graphene-oxide monolayer was characterized through open and closed z-scan experiments, using a nano-second laser operating at a 10 Hz repetition rate and featuring a Gaussian spatial beam profile. The open z-scan revealed a reverse saturable absorption, indicating a positive nonlinear absorption coefficient, while the closed z-scan displayed valley-peak traces, indicative of positive nonlinear refraction. This observation suggests that, under the given excitation wavelength, a two-photon or two-step excitation process occurs due to the increased absorption in both the lower visible and upper UV wavelength regions. This finding implies that graphene oxide exhibits a higher excited-state absorption cross-section compared to its ground state. The resulting nonlinear absorption and nonlinear refraction coefficients were estimated to be approximately ~2.62 × 10 m/W and 3.9 × 10 m/W, respectively. Additionally, this study sheds light on the interplay between nonlinear absorption and nonlinear refraction traces, providing valuable insights into the material's optical properties.
通过开放式和封闭式z扫描实验对氧化石墨烯单层的立方非线性进行了表征，实验使用的是一台重复频率为10 Hz、具有高斯空间光束轮廓的纳秒激光器。开放式z扫描显示出反饱和吸收，表明非线性吸收系数为正，而封闭式z扫描呈现出谷峰轨迹，表明非线性折射为正。这一观察结果表明，在给定的激发波长下，由于在较低可见光和较高紫外波长区域吸收增加，会发生双光子或两步激发过程。这一发现意味着氧化石墨烯与其基态相比表现出更高的激发态吸收截面。由此产生的非线性吸收系数和非线性折射系数估计分别约为~2.62×10 m/W和3.9×10 m/W。此外，这项研究揭示了非线性吸收和非线性折射轨迹之间的相互作用，为该材料的光学特性提供了有价值的见解。
