Optical coating consists of a combination of thin layers. These produce interfering effects that are used to improve the transmission or reflection characteristics of a system. The behavior of an optical coating depends on the number of lambda/4 layers, the thickness of the individual layers, and the differences between the refractive indexes of the individual layers. The most common coatings for precision optics are antireflection coatings (AR), highly reflective coatings (HR), beam splitter coatings, and filter coatings.
Laser line plate mirrors are plate beamsplitters optically coated on the front side of optical parallels or wedge-shaped substrates with a dielectric multilayer coating.