Polarization-Resolved Interferometric Second-Harmonic Generation: Crystallographic Imaging of 2D Heterocrystals

Second-harmonic generation (SHG) is used as a powerful optical polarimetric technique that enables orientational analysis and imaging of various materials. However, two-dimensional (2D) heterostructures, a new class of van der Waals-bound composite crystals, present a challenge in that the superposition of constituent SH fields with material-dependent phase delay needs to be decomposed for the characterization of experimental SHG signals and orientational polarimetry. In this work [1], we devise polarization-resolved spectral phase interferometry and establish a polarimetric analysis for 2D heterobilayers of transition metal dichalcogenides (TMDs) by demonstrating that the orientational information of constituent monolayers can be obtained by a single measurement on heterobilayer areas. Polarized dual-interferograms containing the SHG amplitude, phase, and crystallographic orientation of each monolayer can be Fourier-transformed and matrix-inverted to obtain each of the three quantities. The current method providing a comprehensive SHG description can be applied to heterostructures consisting of more than two monolayers, not limited to TMDs nor 2D materials.