Exact expressions for calculating thin-film absorption coefficients from laser calorimetric data

Analytic expressions for the optical absorptance of a single-layer thin film of arbitrary thickness on a substrate are derived. Multireflections are considered to be coherent within the thin film and incoherent within the substrate; absorptance is assumed to be small. Substrate and thin-film absorptance can be separated by means of two measurements: in one case light enters the coating–substrate system from the coated side, in the other case from the uncoated side. With this technique, optical absorption coefficients of ZnS and hard carbon coatings have been determined using a CO2 laser calorimeter.