The effective fifth-order susceptibility, ${\chi}_{\rm eff}^{(5)}$, of two-dimensional (2D) semiconducting layered transition metal dichalcogenide (LTMD) molybdenum disulfide (${\rm MoS}_2$) is reported here for the first time, to the best of our knowledge. Using the $ Z $-scan technique with a laser operating at 800 nm, 1 kHz, 100 fs, we investigated the nonlinear behavior of ${\rm MoS}_2$ suspended in acetonitrile (concentration, 70 µg/ml). The effective nonlinear refractive index ${{n}_{4,{eff}}} = - ({7.6 \pm 0.5}) \times {10^{- 26}}\; {{\rm cm}^4}/{{\rm W}^2}$, proportional to ${\rm Re}{\chi}_{\rm eff}^{(5)}$, was measured for monolayer ${\rm MoS}_2$ nanoflakes, prepared by a modified redox exfoliation method. We also determined the value of the nonlinear refractive index ${{n}_2} = + ({4.8 \pm 0.5}) \times {10^{- 16}}\;{{\rm cm}^2}/{\rm W}$, which is related to the material’s effective third-order optical susceptibility real part, ${Re\chi}_{\rm eff}^{(3)}$. For comparison, we also investigated the nonlinear response of tungsten disulfide (${\rm WS}_2$) monolayers, prepared by the same method and suspended in acetonitrile (concentration, 40 µg/ml), which only exhibited the third-order nonlinear effect in the same intensity range, up to ${120}\;{{{\rm GW}/{\rm cm}}^2}$. Nonlinear absorption was not observed in either ${\rm MoS}_2$ or ${\rm WS}_2$.

中文翻译：

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半导体二维LTMD MoS _2的五阶光学非线性响应

二维（2D）半导体层状过渡金属二硫化二硫（LTMD）二硫化钼（$ {\ rm MoS}的有效五阶磁化率$ {\ chi} _ {\ rm eff} ^ {（5）} $据我们所知，此处首次报告_2 $）。使用$ Z $ -scan技术和在800 nm，1 kHz，100 fs下工作的激光，我们研究了悬浮在乙腈（浓度为70 µg / ml）中的$ {\ rm MoS} _2 $的非线性行为。有效非线性折射率$ {{n} _ {4，{eff}}} =-（{7.6 \ pm 0.5}）\乘以{10 ^ {-26}} \ 测量{{\ rm cm} ^ 4} / {{\ rm W} ^ 2} $与$ {\ rm Re} {\ chi} _ {\ rm eff} ^ {（5）} $成比例单层$ {\ rm MoS} _2 $纳米薄片，通过改良的氧化还原剥落方法制备。我们还确定了非线性折射率的值$ {{n} _2} = +（{4.8 \ pm 0.5}）\ times {10 ^ {-16}} \; {{\ rm cm} ^ 2} / { \ rm W} $，与材料的有效三阶光学磁化率实部$ {Re \ chi} _ {\ rm eff} ^ {（3）} $有关。为了进行比较，我们还研究了用相同方法制备并悬浮在乙腈（浓度为40 µg / ml）中的二硫化钨（$ {\ rm WS} _2 $）单层的非线性响应，该非线性仅表现出三阶非线性在相同的强度范围内达到最高$ {120} \; {{{\ rm GW} / {\ rm cm}} ^ 2} $。在$ {\ rm MoS} _2 $或$ {\ rm MoS} _2 $中均未观察到非线性吸收$ {\ rm WS} _2 $。