Optical coating

An optical coating is a thin layer or stack of layers applied to an optical surface to control reflection, transmission, absorption, or durability.

Thin-film interference: Interference between light waves reflected or transmitted at boundaries within a thin film. Reflections from coating interfaces reinforce or cancel at selected wavelengths.
Antireflection coating: An optical coating designed to reduce reflection from a surface over a chosen wavelength range. It improves transmission and reduces glare by canceling reflected waves.
Dielectric material: An electrical insulator that can be polarized by an applied electric field. Transparent dielectrics form most low-loss multilayer coatings.
Metallic mirror: A mirror that reflects light using a thin metal film. It offers broad spectral reflection but generally absorbs more light than a dielectric mirror.
Laser-induced damage threshold: The highest laser exposure a material or optical surface withstands before damage occurs under specified conditions. It limits the power a laser coating can safely handle.
Quarter-wave stack: A multilayer optical structure with alternating layers designed around quarter-wavelength optical thickness. Alternating quarter-wave layers form a common design for high-reflectivity mirrors.
Dielectric mirror: A mirror made from alternating dielectric layers that reflect selected wavelengths with low absorption. Its multilayer stack provides high reflectance without a metallic reflecting film.
Metallic coating: A thin metal film applied to a surface to provide reflectance, conductivity, or protection. Metal films reflect broadly, unlike dielectric stacks designed for narrower spectral behavior.
Reflective coating: A surface coating designed primarily to increase the fraction of incident light reflected. It contrasts with coatings optimized to suppress reflection or maximize transmission.
Surface roughness: Small-scale deviations of a surface from its ideal shape, measured across specified spatial scales. Roughness can scatter light and undermine the performance of precision coatings.

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