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When a photon passes from the vacuum to a medium such as water, a polariton forms in the water which carries the energy from the photon at a slower speed through the medium. The polariton being essentially a dipole moment propagating through the medium.

So what happened to the photon? Has it been absorbed? Where has it been absorbed into? Has it been absorbed into an elastic potential between charged particles in the medium? In that case, is it the potential between a nucleus and a bound electron, or is the potential between charges in separate atoms? Or am I totally off base?

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2 Answers 2

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If you talk about visible light passing though water then it is the valence electrons that cause the dielectric response. The photon is, as it were, dressed with a synchronous wave of induce polarisation. When it leaves the water it is a regular vacuum photon again.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – David Z
    Commented May 15, 2018 at 3:10
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Your problem is that you are trying to think solely in corpuscular picture. First, think of EM-field as a wave for a moment. You have a perturbation that causes collective excitation on the boundary surface. Photon energy is converted from the energy of the incoming wave into the energy of the collective modes, kind of like energy of the wind on the lake gets transferred into the energy of the waves. In quantum statistics you will see that the photon gets "annihilated" with the energy being used towards formation of polariton. Very similar to electron-positron annihilation with the emission of gamma-rays.

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  • $\begingroup$ What is the field made of? For that matter what is the wave made of if not photons? Saying wave and field without a medium is just kicking the can down the road. $\endgroup$
    – Bill Alsept
    Commented May 4, 2018 at 21:22
  • $\begingroup$ Please, go read en.wikipedia.org/wiki/Photon making emphasis on particle-wave duality. Also this looks good: phys.ksu.edu/personal/wysin/notes/quantumEM.pdf $\endgroup$
    – MsTais
    Commented May 5, 2018 at 1:11
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    $\begingroup$ Neither particle nor wave describe EM-field correctly. If you will try to stick to solely one or another, you will be in trouble. You question is related to interface between quantum and quasi-classical regimes, that is why thinking of photons as particles only drives you into the corner, in my opinion. $\endgroup$
    – MsTais
    Commented May 5, 2018 at 1:14
  • $\begingroup$ A particle model can derive any light phenomena but a wave model will only derive some. Even then no one can describe lightwaves unless you incorporate photons. $\endgroup$
    – Bill Alsept
    Commented May 5, 2018 at 2:46
  • $\begingroup$ Can you elaborate a bit on “collective modes” and photon “annihilation”? Modes are harmonics that exist between charges in the medium? Does every possible pair of charges have modes? Is there something which annihilates with the photon in the same way that the positron annihilates with the electron? $\endgroup$
    – Arthur Fabian
    Commented May 5, 2018 at 15:34

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