Low-absorption measurement of optical thin films using the photothermal surface-deformation technique

The purpose of this paper is to show both theoretically and experimentally the feasibility of the photothermal surface-deformation (PTD) technique for a highly sensitive, completely contactless detection, as well as a lateral and depth-resolved localization, of absorption in optical thin films. Peculiarities in the interpretation of the measuring signal, such as the influence of the thermal-expansion coefficient of the substrate and the focal diameter of the heating beam, have been pointed out.As a relevant example, the absorption of evaporated ZrO2, single layers on BK 7 substrates has been measured at λ = 515 nm. Their bulk absorption is shown to be strongly influenced by both deposition parameters and the baking procedure.