Complex Refractive Indices Measurements of Polymers in Visible and Near-infrared Bands

The complex refractive indices of polymers have important applications in the analysis of their components and the study of radiation endothermic mechanism. Since these materials have high transmittance in visible to near-infrared ranges, it is difficult to accurately measure their complex refractive indices. At present, the data of complex refractive indices about polymers are seriously lacking, which greatly limits applications of these materials in the field of thermal radiation. In this work, the spectroscopic ellipsometry (SE) combined with the ray tracing method (RTM) is used to measure the complex refractive indices of five polymers, i.e., polydimethylsiloxane (PDMS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), polystyrene (PS) and polyethylene terephthalate (PET), in the spectral range of 0.4-2 μm. The double optical pathlength transmission method (DOPTM) is used to measure the complex refractive indices of three polymers PMMA, polyvinyl chloride (PVC), and polyetherimide (PEI) in 0.4-2 μm. The complex refractive index of PMMA measured by the DOPTM almost coincides with the data measured by SE combined with the RTM. The results show that the trends of complex refractive indices spectra about seven polymers in 0.4-2 μm are similar. This work makes up for the lack of complex refractive indices in 0.4-2 μm for these seven materials, and points out the direction for accurate measurements of the complex refractive indices of polymers with weak absorption.