Mueller Matrix Ptychography for Optical Anisotropy of Triclinic Systems

Characterizing in‐plane optical anisotropy in low‐symmetry 2D materials, especially for triclinic systems where birefringence and dichroism are non‑coaxial, remains challenging. Here, we report a Mueller matrix ptychography (MMP) for characterizing in‐plane optical anisotropy of complex triclinic systems comprehensively and quantitatively. Through the ptychographic amplitude reconstructions combined with Mueller matrix analysis, the diattenuation and retardance of triclinic systems are retrieved as macroscopic manifestations of optical anisotropy. More importantly, leveraging their phase reconstructions with Fresnel equations, we further decouple the refractive index ( n ) and extinction coefficient ( k ) for triclinic systems, revealing the intrinsic property of optical anisotropy. This amplitude‐phase joint characterization framework enables the quantitative imaging of triclinic ReS 2 ’s diattenuation, retardance, as well as in‐plane refractive index and extinction coefficient ellipses, with a spatial resolution of almost one micrometer. This remarkable advancement will provide a new insight into the characterization of in‐plane optical anisotropy in complex triclinic systems, thereby paving the way for their application in novel micro polarization optical elements.