How to understand the negative two-photon transition strength

  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. Greg Bernhardt

    Staff: Admin

    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. 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. 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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