Polarized optical contrast spectroscopy of in plane anisotropic van der Waals materials

Polarized optical contrast spectroscopy is a simple and non-destructive approach to characterize the crystalline anisotropy and orientation of two-dimensional materials. Here, we develop a 3D-printed motorized polarization module, which is compatible with typical microscope platforms and enables to perform broadband polarization-resolved reflectance spectroscopy. As proof of principle, we investigate the in-plane birefringence of exfoliated thin films and few-layer crystals. We compare the measured spectra to a model based on a transfer matrix formalism. Compared to other polarization sensitive approaches, such as Raman or second harmonic generation spectroscopy, optical contrast measurements require orders of magnitude less excitation power densities, which is particularly advantageous to avoid degradation of delicate van der Waals layers.