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Dear CCLers
I came accross some papers which calculate the two
photon absorption cross
section of some organic molecules. Since I have not
been involved in such kind
of calculations, I have some quastions about the
subject.
a) are there any semiempirical or ab initio
prograps which can carry out this task?
b) I saw that instead of calculating the TPA cross
section through the
second order hyperpolarizability, there is a
simplified _expression_ which gives an
estimate of the position and relative strength of
TPA cross section.
2 2
M0k Mkn
__________________
2
(Eok -Eon/2) Γ
In the above _expression_ M is transition
dipole moment. The subscripts 0 and n refer to the initial and final states,
while the subscript k refers to the intemediate virtual state. I understand how
M0n can be calculated, but I do not see
how Mok or Mkn can be
calculated
since the state k is not a real state.
It is obvious that I am missing something....
Thank in advance for your time
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