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 MoS₂. Our method is particularly suitable for applying in vacuum and cryogenic environments while providing optical diffraction-limited resolution and arbitrarily adjustable contrast. Without loss of generality, this contrast-enhanced phase-resolved SHG microscopy can also be used to resolve other non-centrosymmetric inverted structures, e.g. ferroelectric, magnetic, or multiferroic phases.

中文翻译：

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对比增强相位分辨二次谐波发生显微镜

倒置结构（晶体、铁电或磁域）的表征对于新型多态器件的开发和应用至关重要。然而，确定这些倒置结构需要能够揭示其相位相关性的灵敏探头。这里提出了一种对比度增强的相位分辨二次谐波发生（SHG）显微镜，它利用相位可调的 Soleil-Babinet 补偿器以及来自倒置结构和均匀参考的 SHG 场之间的干扰。通过这种方式，这种倒置结构通过SHG的π相位差相关联，并且相位差最终转换为强度对比度。作为演示，我们在两种情况下应用了这种显微镜来确定二维范德华材料 MoS ₂中的倒置晶域。我们的方法特别适合在真空和低温环境中应用，同时提供光学衍射极限分辨率和任意可调对比度。不失一般性，这种对比度增强的相位分辨SHG显微镜还可用于分辨其他非中心对称的倒置结构，例如铁电相、磁性相或多铁性相。