Complex refractive indices measurements of polymers in infrared bands

Polymers are widely used in many fields such as radiative cooling, infrared stealth, optical fibers and solar cells. In this work, the complex refractive indices of seven polymers such as polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polyetherimide (PEI) are measured by spectroscopic ellipsometry (SE) combined with the ray tracing method (RTM) from near-infrared to mid-infrared bands (2–20 µm). The measured results of PDMS have been proved to be accurate by comparing them with previous data in the literature. The obtained refractive indices of polymers in this paper have been compared with the results calculated by the Kramers-Kronig relations. Finally, we analyze the reasons of absorption peaks of these materials in infrared bands by the vibration of chemical bonds in molecules.