How to understand the negative two-photon transition strength

[sandf]

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.
Lan

 

[Greg Bernhardt]

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?

 

[sandf]

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?

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.

Bests
Lan

 

[Zarqon]

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.