Application Galerie

Anti-reflective coatings are frequently used in optical systems to reduce the amount of stray light produced when a beam of light crosses from one medium into another medium with a different refractive index. The simplest example of an anti-reflective coating is a quarter-wavelength layer, in which the thickness of a monolayer dielectric film is adjusted to be one fourth of the optical wavelength. Although a single-layer coating can reduce the reflectance to zero for light at a specific wavelength and angle of incidence, the reflectance can be substantially larger for other wavelengths. One possible solution is to use a multilayer coating that gives consistently low reflectance over a wider spectral band.

In this tutorial, light crosses a boundary between two media with different refractive indices at normal incidence. The reflectance of two different multilayer coatings is compared over a wide spectral range: a quarter-quarter coating (two layers), and a quarter-half-quarter coating (three layers). The quarter-half-quarter coating is shown to have more consistently low reflectance across most of the visible spectrum.