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Photon absorption via changing EM field

  1. Feb 25, 2010 #1


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    Does it work like that.. that a changing EM field in-phase (actually, like.. 180 degre (spell?) out-of phase) with the incoming photon would absorb it?

    .. when sound waves of 180 degre.. (spell) out of phase with each other would cancel each other out.
    The same thing would happen with EM radiation - photons, right? Yes, think i know that.. :)

    And if the EM field changing in (out of) phase would absorb it - it wouldn't do it instantly. It would decrease in energy and while it decreases in energy, it would decrease in frequency, right? ..

    (edited: and I just thought - if it changes frequency, it is not in-phase anymore...)

    Another question while we are at this - where does the energy go in two wave cancellation?
    Last edited: Feb 25, 2010
  2. jcsd
  3. Feb 26, 2010 #2
    In terms of, say, atomic absorption, there is indeed a gradual process, but the intermediate states are not reduced frequency, but rather an increase in the probability to find the atom in an excited state.

    An atom that is in the process of getting excited (is in a superposition of ground and excited state) can be seen as radiating a field with the opposite phase as the photon that gets absorbed. During the process, the probability of the atom being in the excited state increases and the probability of having the photon decreases. This conserves the total energy while still allowing te photon to have the same frequency during the process.

    If you're interested in a more visual picture of this process I can recommend reading about the Bloch sphere.
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