Fig. 4: Confirmation of optical anisotropy of van der Waals GeS2 by near-field measurements.
a Schematics of the s-SNOM experimental configuration for GeS2 sample on top of Schott glass substrate. b AFM image of the studied GeS2 flake’s corner. The inset shows the cross-section height plot. c, d Near-field images: amplitude Amp(E) and phase Arg(E) of the electric field at the incident wavelength of λ = 1000 nm (the other wavelength images are displayed in Supplementary Note 6). e The line profiles are taken from (c) and (d). f Fourier transform amplitude of the complex near-field signal presented in (e). Transfer-matrix calculations for propagating modes GeS2 flake along the a (g) and b (h) crystallographic directions. Dashed blue lines denote TM and TE fundamental modes. The green dots indicate experimental data points obtained from s-SNOM imaging. In calculations, we used the permittivity extracted from the ellipsometric measurements as an input
