Abstract

Four effects which depend on the columnar structure of thin films are discussed. The porous nature of many coatings permits atmospheric water to penetrate into the layers causing the refractive index to increase and the spectral profile to shift towards the red. In some cases the process is slowed or stops when a cover is cemented over the air-film surface. A narrow band interference filter with 'locked' patches (Fig.1) forms a suitable subject for the observation of scatter from absorbed water. To a first approximation the patches can be treated as a random array of identical sets of annular apertures, and the distribution of scattered light as the diffraction pattern of a single set of apertures.

© 1984 Optical Society of America