Spectral Filters Spectral Filters Optical filters are often used to attenuate certain wavelengths of light and produce an overall desired detector response.
Interference filters rely on harmonic interference between waves to provide very narrow passbands.
Thin metal films are spaced half the desired wavelength apart by a dielectric spacer. Interference filters are capable of bandwidths less than 10 nm. Absorptive filters typically consist of glass that has been doped with a concentration of dye that absorbs particular colors. Since spectral transmission varies logarithmically with thickness, the band pass can be reduced by thickening the filter. Internal transmittance is greater than external transmittance due to reflection losses.