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Photon's energy

  1. Feb 4, 2013 #1
    If you have one high energy photon and you collect it together with another, does there energy combined into one high energy or do they stay as seperate energies
  2. jcsd
  3. Feb 4, 2013 #2
    What do you mean by 'collect it together' ?

    If everyday situations, the color [frequency, energy] of individual photons are based on their emission conditions, and those remain individual, like their energy [color]. So we see different colors coming to earth, for example, from nearby stars.
    Last edited: Feb 4, 2013
  4. Feb 4, 2013 #3


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    Two photons remain as two photons. If both of them happen to interact with the same system (say an atom, for instance) then their effects can add. One could raise an atom to a high energy state then the next could completely ionise that atom. But the photons remain totally 'unaware' of each other whilst in space.
    Until a photon is 'observed' in some way, one can't tell anything about where it is or when it's where it is, even. It really only exists as an entity whilst it is doing its interacting with something. It's really only a matter of belief whether they actually exist on the way from source to receptor.
  5. Feb 4, 2013 #4
    There's a phenomenon known as two photon absorption, where a molecule absorbs two photons at the same time to jump to a higher energy level, where the energy of the transition equals the sum of the two photon energies. This is a nonlinear optical effect which occurs relatively rarely.
  6. Feb 4, 2013 #5
    so if photons with a high enegry (lets say its wave length is the plank length) where shot through a medium, would there be the energy of two plank length atoms or is that the limit to how much energy can be
  7. Feb 4, 2013 #6


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    The inverse can happen. Emission of two photons from an excited atom, on the way to a ground state, is not uncommon - but then the atom 'can make the choice' about the energies of the photons involved and the timing of the events.
  8. Feb 4, 2013 #7
    As already said, it is possible. It is a non-linear process of third order called two-photon absorption and it is not so unusual. It is used for energy(frequency) doubling e.g. in green laser pointers. Most non-centrosymmetric crystals present this effect, but only in a few crystals it is sufficiently efficient for practical purposes.
  9. Feb 4, 2013 #8
    We don't know what happens at the Planck length. Maybe nothing special at all. Our current theory has no limit on energy. If you add two photons' energies, the wavelength would be divided by two.

    But if you fire such a photon into a medium, you'll probably get an explosion of particles created when the photon hits the medium.
  10. Feb 4, 2013 #9
    Is that possible a molecule absorbs two photons at the same time to jump to a higher energy level and then emission one higher energy photon and back to before place ?

    example : electron absorbs 2 photon by energy 10 and 20 eV and jump up from 2 to 3 energy level and emission a 30 eV photon and back to 2 energy level ?
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