Thin-film optics is the branch of
optics that deals with very thin structured layers of different materials. In order to exhibit thin-film optics, the thickness of the layers of material must be on the order of the wavelengths of visible light (about 500
nm). Layers at this scale can have remarkable reflective properties due to light wave
interference and the difference in
refractive index between the layers, the air, and the substrate. These effects alter the way the optic
reflects and
transmits light. This effect, known as
thin-film interference, is observable in
soap bubbles and oil slicks.