Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS ₂ using multiphoton microscopy

We report second- and third-harmonic generation in monolayer MoS2 as a tool for imaging and accurately characterizing the material's nonlinear optical properties under 1560 nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second- and third-order nonlinear sheet susceptibility magnitudes, obtaining values of | \χ _⁽²⁾| \\ =2.0\× 10⁻²⁰ m2 V−1 and, for the first time for monolayer MoS2, | \χ _⁽³⁾| =1.7\× 10⁻²⁸ m3 V−2. These sheet susceptibilities correspond to effective bulk nonlinear susceptibility values of | \χ _⁽²⁾| =2.9\\ \× 10⁻¹¹ m V−1 and | \χ _⁽³⁾| =2.4\× 10⁻¹⁹ m2 V−2, accounting for the sheet thickness. Experimental comparisons between MoS2 and graphene are also performed, demonstrating ~3.4 times stronger third-order sheet nonlinearity in monolayer MoS2, highlighting the material's potential for nonlinear photonics in the telecommunications C band.