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Can you combine wavelengths to ionize atoms

  1. Apr 2, 2014 #1
    If I have an atom with energy levels of -4 ev, -2 ev -1 ev and 0 ev and I radiate it with photons which cover a continuous range from 0 to 2 ev is it not possible for a 2 ev photon to move the electron from -4 to -2 and then a 1 ev photon to move it from -2 to -1 and then a 2 ev photon to free the electron with a kinetic energy of 1 ev? Most material talks about a minimum frequency to eject an electron but I think that only applies it the source is a single frequency. Am I correct? Thanks!
  2. jcsd
  3. Apr 2, 2014 #2


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    It is possible, but the absorption cross-section for the entire process is low, i.e. it has a very low probability of happening.

    This is similar to a multi-electron photoemission where photons with energy LESS than the work function of the material can still cause the emission of photoelectrons. The caveat here is that it must be a very intense light source, often a high-powered laser. This is because after the first excitation, the electrons are in the excited state only for a very, VERY, short amount of time. If it does not encounter another photon within that time that will cause another excitation, it will decay back to the ground state and you will have to start all over again.

    So the mechanism here requires the second excitation to occur while the system is still under the first excitation state. The probability here is considerably lower (often 2 to 3 orders of magnitude, or more) lower than a single-photon excitation.

  4. Apr 2, 2014 #3
    Thanks! I am teaching the second semester of Physics for the first time and I thought that was how it worked but I needed confirmation.
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