Thin-film interference

Summary

Thin-film interference is the interference of light reflected from the top and from the bottom surface of a thin layer. The two reflected waves differ by twice the optical thickness of the layer and by possible phase jumps at the surfaces. So some wavelengths are reflected strongly and others weakly, depending on the thickness. It explains the colours of soap bubbles and oil films, and it is the principle of antireflection coatings and dielectric mirrors.