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When we derive refraction and reflection laws for a generical plane wave on a surface, we say that reflected and refracted must be in phase with the incident wave. Why a medium cannot do a sphased reaction beside incident wave? Sorry for my trivial question.

Qmechanic
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Boy S
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It is possible. Take a look at phase conjugated mirror on Wikipedia.

Also, phase shifts do happen on reflection from flat surfaces -- all the time. It's called the Goos-Hänchen effect. It's just very very small, so that's probably why you ignore it in your derivation.

ptomato
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  • Thank for the answer! Phase conjugated mirror is optically non linear: do you mean that this effect is a non linear effect? If yes, why in linear conditions you haven't phase shifts in reflection? – Boy S Dec 16 '10 at 19:04
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    A phase conjugated mirror's effect is non-linear, but the Goos-Hänchen effect takes place in linear media. It has to do with the penetration depth of the wave into the medium, if I remember correctly. – ptomato Dec 16 '10 at 21:58