ABSTRACT
An optical filter attenuates particular wavelengths of radiation while passing others with relatively little change. The attenuation can be effected by absorption in the body of the filter or interference effects in a single or multilayer coating. Neutral density filters attenuate light without changing the spectral quality of the light. A spectral filter is a device which selects specific wavelengths for absorption with high precision. A major application of absorption filters is the selective absorption of certain band passes in the visible spectrum, or a color filter. Selective reflection filters depend on the reststrahlen reflection of certain crystals. Absorption filters are produced in a variety of host materials such as gelatin, glass, liquid, or plastic where the absorbing component actually absorbs the radiation. The interference filter depends on multilayer dielectric-metal stacks to control the transmission or reflection of particular bandpasses by means of constructive and destructive interference.
