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, χ, of tungsten diselenide (WSe). 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 WSe. We register a value of |χ| ≈ 0.