Optical coatings are used to enhance the properties of an optical component. An anti-reflection coating can reduce the reflection at each surface and a highly reflective dielectric coating can also be applied to increase reflectivity.
An optical coating is composed of a combination of thin layers of materials such a oxides, metals, or rare earth materials. The performance of an optical coating is dependent on the number of layers, their thickness, and the refractive index difference between them.
Thin film optical coatings are typically created by depositing dielectric and metallic materials, such as tantalum pentoxide, aluminum oxide, alternating thin layers. That thin film layers alternate between high index of refraction and low index of refraction, thereby inducing the interference effects needed.