Characterization of the second- and third-harmonic optical susceptibilities of atomically thin tungsten diselenide

We report the first detailed characterization of the sheet third-harmonic optical susceptibility,chi((3))(s), of tungsten diselenide (WSe2). With a home-built multiphoton microscope setup developed to study harmonics generation, we map the second and third-harmonic intensities as a function of position in the sample, pump power and polarization angle, for single-and few-layers flakes of WSe2. We register a value of vertical bar chi((3))(s)vertical bar approximate to 0.9 x 10(-28) m(3) V-2 at a fundamental excitation frequency of h omega = 0.8 eV, which is comparable in magnitude to the third-harmonic susceptibility of other group-VI transition metal dichalcogenides. The simultaneously recorded sheet second-harmonic susceptibility is found to be vertical bar chi((2))(s)vertical bar approximate to 0.7 x 10(-19) m(2) V-1 in very good agreement on the order of magnitude with recent reports for WSe2, which asserts the robustness of our values for vertical bar chi((3))(s)vertical bar .