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, χ(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 |χ(3)s| ≈ 0.9 × 10−28 m3 V−2 at a fundamental excitation frequency of ℏω = 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 |χ(2)s| ≈ 0.7 × 10−19 m2 V−1 in very good agreement on the order of magnitude with recent reports for WSe2, which asserts the robustness of our values for |χ(3)s|.

Nonlinear optics of two‐dimensional transition metal dichalcogenides

“…Copyright 2017, Nature Publishing Group. E and F, Polarization‐dependent SHG and THG of monolayer WSe 2 , respectively . Copyright 2018, Nature Publishing Group.…”

“…When the excitation polarization is parallel to the analyzer, I 2 ω = I 0 cos 2 (3 θ + φ 0 ), while I 2 ω = I 0 sin 2 (3 θ + φ 0 ) when the excitation polarization is crossed with the analyzer, where θ is the angle between the laser polarization and the x direction (armchair direction) in TMDs plane and φ 0 is the initial angle between laser polarization and armchair direction. A 6‐fold pattern of SHG intensity can be resolved by rotating the monolayer sample, with fixed analyzer and excitation polarization (Figure D) . By fitting the 6‐fold pattern with the cos 2 (3 θ + φ 0 ) or sin 2 (3 θ + φ 0 ) function, φ 0 can be resolved and the initial orientation of the crystal can be determined.…”

“… χ (3) of all MoS 2 , WS 2 , WSe 2 , and MoSe 2 were estimated to around 1 × 10 −19 m 2 /V 2 . There are two methods to estimate χ (3) .…”

“…A 6-fold pattern of SHG intensity can be resolved by rotating the monolayer sample, with fixed analyzer and excitation polarization ( Figure 1D). 53 By fitting the 6-fold pattern with the cos 2 (3θ + φ 0 ) or sin 2 (3θ + φ 0 ) function, φ 0 can be resolved and the initial orientation of the crystal can be determined. This polarization dependence was widely utilized to probe the crystal orientation of h-BN and monolayer TMDs.…”

“…χ (3) of all MoS 2 , WS 2 , WSe 2 , and MoSe 2 were estimated to around 1 × 10 −19 m 2 /V 2 . 52,53,62,82 There are two methods to estimate χ (3) . Wang et al treat a seven layers of MoS 2 flake as an bulk material, solve the coupled-wave equation, and deduce the effective χ (3) around 10 −19 m 2 /V 2 , which is three-order of magnitude smaller than that of the single layer graphene.…”