Measuring the refractive index and thickness of thin transparent films: method

A new method is described for the determination of refractive index of transparent films on transparent substrates based on the observation of an interference pattern in the light scattered by the film. The pattern consists of a series of bright rings caused by multiple reflections inside the film; when the film index is lower than the substrate index, a measurement of the diameters of two rings uniquely determines both film index and thickness. Accuracies of 1 part in 10(3) for the refractive index and 1 part in 10(2) for the thickness are obtained. Examples of application to films of several thermally evaporated materials are given.