An interference filter uses wave interference in a layered optical structure to transmit or reject selected wavelengths. The accumulated optical path length makes reflected contributions reinforce or cancel differently across the optical spectrum.
A narrow-band example can isolate emission before a photodetector or reject an excitation beam in fluorescence microscopy. Tilting the filter changes the propagation angles and optical paths inside its layers, shifting the transmitted band. A filter characterized in a collimated beam may therefore behave differently in a strongly converging beam; temperature and polarization can also affect transmission.
An interference filter, also known as an optical interference filter or thin-film filter, is a type of optical filter that selectively transmits light of certain wavelengths while reflecting others, based on the principle of interference. These filters are often made up of multiple layers of thin films, typically of different refractive indices, deposited on a glass or plastic substrate.
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