Contrast-enhanced phase-resolved second harmonic generation microscopy

The characterization of inverted structures (crystallographic, ferroelectric, or magnetic domains) is crucial in the development and application of novel multi-state devices. However, determining these inverted structures needs a sensitive probe capable of revealing their phase correlation. Here a contrast-enhanced phase-resolved second harmonic generation (SHG) microscopy is presented, which utilizes a phase-tunable Soleil-Babinet compensator and the interference between the SHG fields from the inverted structures and a homogeneous reference. By this means, such inverted structures are correlated through the π-phase difference of SHG, and the phase difference is ultimately converted into the intensity contrast. As a demonstration, we have applied this microscopy in two scenarios to determine the inverted crystallographic domains in two-dimensional van der Waals material MoS