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How to understand the negative two-photon transition strength

  1. May 18, 2014 #1
    Dear all,
    I have calculated the rotationally averaged two-photon transition
    strength (DeltaTPA) using the CCSD response approach. Degenerate TPAs of ten excited states have been calculated. For most of the excited states considered, I got the positive DeltaTPAs, while for some excited states, I got the negative DeltaTPAs. The negative DeltaTPA will lead to the negative TPA cross section, then to the negative TPA absorption coefficience (beta). My question is:
    whether the negative beta can be related to the saturable absorption process.
    Any references and comments are appreciated.
    Best regards.
  2. jcsd
  3. Jun 11, 2014 #2
    I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
  4. Jun 11, 2014 #3
    Dear Bernhardt,
    Thanks for your attention. I also ask for help on the forum of DALTON program
    which implements the CCSD response calculation for TPA. Unfortunately, I haven't gotten the response.

  5. Jun 12, 2014 #4
    I'm not familiar with with the specific technique you have used but I can give a more general comment.

    Generally, when one is talking about negative absorption coefficients, what is meant is that you have a gain situation, i.e. stimulated emission, most often coming from some form of inverted population.
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