### How to understand the negative two-photon transition strengt

Posted:

**19 May 2014, 03:23**Dear all,

How to understand the negative rotationally averaged two-photon transition strength (DeltaTPA)

I have calculated the two-photon absorption (TPA) of a system using the CCSD response approach. My system has a C2v symmetry. TPAs of three excited states for each irreducible representation 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 coefficient (Beta). My question is:

whether the negative Beta can be related to the nonlinear saturable absorption process.

Any references and comments are appreciated.

Best regards.

Lan

How to understand the negative rotationally averaged two-photon transition strength (DeltaTPA)

I have calculated the two-photon absorption (TPA) of a system using the CCSD response approach. My system has a C2v symmetry. TPAs of three excited states for each irreducible representation 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 coefficient (Beta). My question is:

whether the negative Beta can be related to the nonlinear saturable absorption process.

Any references and comments are appreciated.

Best regards.

Lan