Extraction of refractive index data from optical measurements of flat, rough and inhomogeneous thin films

Unlike other physical parameters the refractive index of a material is not directly accessible to experiments. Yet, we can use optical measurements of transmission T and reflection R of a thin layer to extract its dielectric function. Often times this extraction is performed based on physical models that need to be chosen carefully according to the specific material type. Here we present a procedure based on the transfer-matrix method (TMM) that allows the exclusive mathematical recalculation of the complex refractive index (n,k) from measured (T,R). This means no particular material model for the film investigated is required. Moreover, we will address common imperfections of thin layers like surface roughness or internal roughnesses (voids), which usually destroy the applicability of the TMM, by adapting the model to consider these properties. By comparing (T,R) calculated as a function of the desired optical constants (n,k) with the measured data in an iterative minimization process of the deviation the desired dielectric function becomes accessible. This procedure under consideration of surface and internal roughnesses for a multilayer stack of thin films and thick substrates as well as with the option of an effective medium is possible via our simulation tool RefDex.

After the physical background presentation of prof. Martina Schmid, dr. Phillip manley presents simulations hands-on sample characterization by using proposed tools.