Second-Harmonic Young's Interference in Atom-Thin Heterocrystals.

Second-harmonic generation (SHG) is a nonlinear optical process that converts two identical photons into a new one with doubled frequency. Two-dimensional semiconductors represented by transition-metal dichalcogenides are highly efficient SHG media because of their excitonic resonances. Using spectral phase interferometry, here we directly show that SHG in heterobilayers of MoS and WS is governed by optical interference between two coherent SH fields that are phase-delayed differently in each material.