Investigation of the Light Reflection from Dielectric Thin Films Coated on Substrates

Abstract

We investigated the light reflection from thin films coated on substrates. Using a prism with a high refractive index as the incident medium, the phenomena of the total internal reflection (TIR) of the prism/film/substrate system and the light coupling into the optical waveguide formed by the air/film/substrate system were comprehensively studied and compared. If the refractive index of the thin film is greater than that of the substrate, within the TIR region of the substrate, sharp reflection minima occur at specific angles where the waveguide modes are excited, that can be used to accurately measure the refractive index and thickness of a thin film. On the other hand, if the refractive index of the thin film is smaller than that of the substrate, such waveguide modes do not exist. In this case, although not so distinct as a bulk medium, the TIR effect of the thin film is still observable, accompanied by an interference pattern. In this study we analyzed the overall reflection phenomena occurring from prism/film/substrate structures, to investigate the possibility of measuring the refractive index of a thin film in both cases.