Abstract

Second-harmonic generation (SHG) is a powerful measurement technique to analyse the symmetry properties of crystals. Mechanical strain can reduce the symmetry of a crystal and even weak strain can have an immense impact on the SHG intensity along different polarization directions [1]. The impact of strain on the SHG can be modelled with a second-order nonlinear photoelastic tensor [2,3]. We find that the photoelastic tensors depends highly on the excitation wavelength. We investigated the influence of strain on SHG for MoS₂, MoSe₂, WS₂, and WSe2 monolayers. In order to quantify the strain induced anisotropy in the polarization resolved SHG we define two parameters. The Distortion $D={\left(\frac{A-B}{A+B}\right)}^2$, which is the ratio of the minima to the maxima of the envelope function of the polarization resolved SHG and the Intensity I = π (A² + B²), which is the integral of the SHG intensity over all polarization directions.

© 2019 IEEE