Determining the absorption coefficient of absorbing thin films with optical waveguides

A new simple method of determining the absorption coefficient of absorbing thin films is proposed as an application of the complex propagation constant of a guided wave in a thin film optical waveguide. This method was applied to both cases as examples: low index (polyurethane film top layer containing rhodamine 6G dye) and high index (evaporated ZnSe film top layer) absorbing top layers on the main glass guide. The absorption coefficients so determined were compared with the values given by Lambert's method.