Dear all,(adsbygoogle = window.adsbygoogle || []).push({});

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

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# How to understand the negative two-photon transition strength

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