Measurement of Refractive Index and Thickness of Thin Films Via Polarization‐Projection Interferometry

Abstract Accurate characterization of the complex refractive index () and thickness () of thin films is essential for advancing optical and photonic technologies. In this work, a polarization‐projection interferometric method (PPIM) is presented that enables the simultaneous extraction of () with high precision using transmission measurements. By measuring and analyzing both the amplitude and phase of the transmitted light, PPIM achieves superior accuracy and robustness compared to conventional ellipsometry, especially for ultrathin and birefringent films. Moreover, the extracted thicknesses show excellent agreement with scanning electron microscopy (SEM) measurements, confirming the reliability of PPIM. With its precision and versatility, PPIM offers a powerful and flexible tool for thin‐film metrology in optics, materials science, and integrated photonics.