Nondestructive measurement of the thickness and refractive index of polymer thin films using a single-frequency terahertz Mueller matrix ellipsometry

Terahertz Mueller matrix ellipsometry is a nondestructive technique based on terahertz waves that can measure film thickness and optical constants with high accuracy. We propose a single-frequency terahertz Mueller matrix ellipsometry based on a dual rotating compensator configuration, which utilizes terahertz waves to achieve high-precision nondestructive measurements of the thickness and refractive index of polymer films. The system realizes the fully polarized incidence of the terahertz beam by rotating the compensator, and establishes a complete polarization measurement scheme by measuring the outgoing light intensity of the two compensators at different angles. Based on the coherent light scattering model, we developed a corresponding data processing algorithm and realized the simultaneous and accurate determination of the film thickness and refractive index through the extraction and inverse calculation of the full Mueller matrix elements. The experimental results show that the system has excellent measurement accuracy and reliability. This research opens up what we believe to be a new research pathway for the characterization and detection of thin film materials, which has an important application value in the field of material science and industrial testing.