What is an interference filter?


Interference filters consist of several thin layers (typically between 10nm and 1µm) of dielectric transparent materials with different refractive indices applied to a substrate. These layer systems are constructed in such a way that they transmit light of a certain wavelength and reflect other wavelengths. This is achieved by the interference of light waves that are transmitted and reflected at the interfaces between the layers. The thickness and refractive index of the layers are chosen so that the transmitted and reflected waves interfere constructively or destructively, depending on the wavelength of the light. In this way, interference filters can be designed so that they are transparent for a desired wavelength range if they were to reflect light with other wavelengths. Long-pass, short-pass and band-pass filters can be produced in this way. If steep edges are required, interference filters are the best option. For applications where reflection is undesirable, for example, absorbing colored glass filters are more suitable.

How does an interference filter work?
A system of thin dielectric layers with different refractive indices acts as a filter due to interference effects at the interfaces between the layers and allows certain wavelengths to pass through while other wavelengths are reflected.
What are interference filters used for?
Interference filters can be designed as long-pass, short-pass and band-pass filters and are widely used in optical measurement technology devices.