Abstract

Reduction of losses in thin films is particularly important because losses limit multilayer performances. In theory, losses can be divided into scattering and absorption. In absorption, the energy lost from the primary beam is dissipated and appears as heat. Absorption is a material property, which can be intrinsic or due to impurities. Scattering is usually caused by volume and surface due to defects in the film. Roughnesses of the substrate and interfaces are the sources of surface scattering losses, and volume defects appear as local variations of optical constants and are usually caused by dust particles or pinholes in the film. In order to separate the different classes of losses, we use thermal deflection measurements to track the losses in a thin film used as a waveguide. If the guide supports more than one mode, the losses in each mode can be tracked. The theoretical study shows that the modes respond differently according to the loss mechanism, and this can be used to separate scattering and absorption losses. As an example, the technique is applied to two Ta₂O₅ films whose extinction coefficient is about 10⁻⁵; we study the consequences of layer annealing by measurements performed before and after the thermal process.

© 1990 Optical Society of America