Simultaneous Determination of Transition Dipole Moment Orientation and Refractive Index in Morphologically Non‐Uniform Nanoscale Films

Abstract A high‐precision, single‐shot technique simultaneously quantifies the refractive index and transition dipole moment orientation in nanoscale emissive films using Fourier imaging microscopy. Direct capture of momentum‐space ( k ‐space) emission patterns in a polarization‐resolved setup enables characterization of anisotropic optical properties. This approach overcomes limitations of conventional ellipsometry and angle‐dependent photoluminescence measurements, which typically require predefined refractive index models and atomically smooth interfaces. The method determines anisotropic refractive indices and in‐plane transition dipole moment orientations across various emissive systems, including organic films, quasi‐2D perovskite layers, and quantum dot layers, even in the presence of nanoscale morphological disorder. The experimental result yields parameters with a precision of within 1% and 0.01 for transition dipole moment orientation and refractive index, respectively. The measured refractive index shows good agreement with conventional ellipsometry measurements. The extracted parameters strongly correlate with enhancements in optical outcoupling efficiency. These findings highlight the utility of Fourier imaging microscopy as a diagnostic tool for designing and optimizing next‐generation optoelectronic devices.