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Is there a type of glass, mirror or lens that allows only lights of amplitude equal to or greater than a fixed value to pass/reflect through them?

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up vote 15 down vote accepted

Yes, there are. Such materials are called "saturable absorbers," and are (or at least, have been) used as switches in some laser designs. The one I recall is a nickel acetate dye, although there are others. Basically, the molecules absorb single photons at the laser wavelength, but when the intensity is great enough that two photons are absorbed simultaneously (or precisely, within the decay time of the single-photon excited state), the excited molecule no longer absorbs at that wavelength and the high-power beam is transmitted. This was done in, e.g., early hand-held laser rangefinders to produce a higher-power, shorter length output pulse.

Interestingly enough, there are also saturable transmitters. Essentially this is what's layered onto eyeglasses to produce those lenses which are sunglasses in bright light but clear in dim light.

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