![]() More of the reflected light is in the red and blue extremes of the visible spectrum. This is a result of optimizing the antireflection coating for the midrange wavelengths, the greens. You may have noticed that the lenses of your camera or binoculars have a purplish tint to them when viewed at a glancing angle like the illustrations below. The reflected intensities at the extreme wavelengths of the visible spectrum are: Reflected intensity at 400 nm: % ![]() Without the coating, the reflected intensity would be %. Since these reflections are 180° out of phase, the resulting reflected intensity (square of amplitude) is The amplitude of reflection off the back surface (coating-to-glass) is The amplitude of reflection from the first surface (air-to-coating) is With the assumption of a coating thickness of a quarter wavelength in the medium, the reflection can be calculated by using the normal incidence reflection coefficients. Single layer antireflection coatings are generally calculated for a midrange wavelength like 550 nm (green). The colors used are to distinguish the layers, but not otherwise significant. Multiple layers are more effective over the entire visible spectrum. Thin filmsĪ single layer anti-reflection coating can be made non-reflective only at one wavelength, usually at the middle of the visible. If the coating is a quarter wavelength thickness and the coating has an index of refraction less that the glass it is coating then the two reflections are 180 degrees out of phase. If these waves are out of phase, they partially or totally cancel. The idea behind anti-reflection coatings is that the creation of a double interface by means of a thin film gives you two reflected waves. Multi-layer coatings can reduce the loss over the visible spectrum. A single quarter-wavelength coating of optimum index can eliminate reflection at one wavelength. Thin film anti-reflection coatings greatly reduce the light loss in multi-element lenses by making use of phase changes and the dependence of the reflectivity on index of refraction. ![]() Anti-Reflection Coatings Anti-Reflection Coatings ![]()
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