anti-reflection coating

Definition: Transparent material applied in a thin coat of one or more layers to a lens surface to reduce the amount of light reflected from the surface. * The conditions are: (a) ideal thickness for a single-layer coating is one-quarter of the wavelength at which reflectance is to be minimized and (b) the refractive index of the material should equal the square root of the product of the indices of the materials on either side of the coating (therefore it nearly equals the square root of the refractive index of the glass as the other material is usually air).
Multi-elements, mighty reflection
If it were not for anti-reflection coatings of incredibly high effectiveness, it would be impossible to have today's lenses using multiple elements - more than 12 is not unusual these days - for the numerous interfaces would reflect so much light, images would be very dim and very flat.

Related Terms: vacuum deposition

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