INTERFERENCE FILTER

An optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. Note 1: An interference filter may be high-pass, low-pass, bandpass, or band -rejection. Note 2: An interference filter consists of multiple thin layers of dielectric material having different refractive indices. There also may be metallic layers. Interference filters are wavelength -selective by virtue of the interference effects that take place between the incident and reflected waves at the thin-film boundaries.