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

Abstract

We report the first detailed characterization of the sheet third-harmonic optical susceptibility, $\ddot{I}{‡}_s^{(3)}$, of tungsten diselenide (WSe${}_2$). With a home-built confocal 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 WSe${}_2$. We register a value of $|\ddot{I}{‡}_s^{(3)}|\approx$ 0.91 $\times$ 10${}^{-28}$ m${}^3$ V${}^{-2}$ at a fundamental excitation frequency of $\hslash \ddot{I}‰$ = 0.8 eV, which is comparable in magnitude to the third-harmonic susceptibility of other group-VI transition metal dichalcogenides. The simultaneously recorded second-harmonic susceptibility is found to be $|\ddot{I}{‡}_s^{(2)}|\approx$ 0.70 $\times$ 10${}^{-19}$ m${}^2$ V${}^{-1}$ in very good agreement on the order of magnitude with recent reports for WSe${}_2$, which asserts the robustness of our values for $|\ddot{I}{‡}_s^{(3)}|$.

20 pages, 8 figures, 1 table