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Photons in amorphous glass slow because?

  1. Jan 8, 2012 #1
    In solids it is the interaciton b/w the phonons and photons that give a lower effective speed. not absorption & re-emmision. (see ZapperZ's post: https://www.physicsforums.com/showthread.php?t=511177 [Broken])

    but in amorphous glass there are no phonons. So why does light 'slow down'?

    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jan 8, 2012 #2
    The phonons are there.
  4. Jan 8, 2012 #3
    what do you mean? they are localized dispersion relations for different zones, corresponding to some small order?
  5. Jan 8, 2012 #4
    I mean you stated that amourphous glass has no phonons. This is incorrect.

    In classical terms you have dielectric polarization. In quantum terms you have phonons. Either way you slice it, you have slower light propagation.
  6. Jan 9, 2012 #5
    well there is some interaction b/w the photon and the phonons, like in ion trapping, where you get dressed states of the phonon ladder and the qubit (some transition in say Yb+ (Monroe research)) which atomic transition (qubit) the light field can interact with.
    on the other hand this is some microscopic mechanism and i relaize now not the one we see in bulk, since we can almost treat that classically as the e&m field driving atoms physically rather than by some inner atomic transition.

    anyway, i remain confused

    does Kittel or Ashcroft & Mermin talk about this somewhere?
  7. Jan 9, 2012 #6
    Kittel has a paper where he discuss thermal conduction in glasses in terms of phonons.
    It is quite old: Interpretation of the Thermal Conductivity of Glasses, Physical Review, vol 75 no 6 page 972 (1949).
    He mentions phonons in liquids as well.
    There are more recent papers treating amorphous materials (especially amorphous metals) and using the concept of phonon.
    Vibrations of the lattice exist no matter if the lattice is periodic or not.
  8. Jan 11, 2012 #7
    thank you
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