How to understand the negative two-photon transition strength

In summary, Lan has used the CCSD response approach to calculate the rotationally averaged two-photon transition strength (DeltaTPA) for ten excited states. Most of the excited states have resulted in positive DeltaTPAs, but some have resulted in negative DeltaTPAs. This negative value can lead to a negative TPA cross section and TPA absorption coefficient (beta). Lan's question is if this negative beta can be linked to the saturable absorption process. He has asked for references and comments, but has not received any responses yet.
  • #1
sandf
21
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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
 
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  • #2
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?
 
  • #3
Greg Bernhardt said:
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
 
  • #4
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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1. What is the negative two-photon transition strength?

The negative two-photon transition strength is a measure of the probability of a two-photon transition between two energy states in a system. It is typically represented by the symbol W and is used to describe the rate at which this transition occurs.

2. How is the negative two-photon transition strength calculated?

The negative two-photon transition strength is calculated by taking into account the energy levels of the system, the transition dipole moment, and the density of states at the initial and final energy levels. It is typically calculated using quantum mechanical calculations or experimental techniques.

3. What factors affect the negative two-photon transition strength?

The negative two-photon transition strength can be affected by various factors such as the energy difference between the two states, the transition dipole moment, and the density of states. Additionally, the presence of external fields and the symmetry of the system can also influence the strength of the transition.

4. How does the negative two-photon transition strength relate to other transition strengths?

The negative two-photon transition strength is related to other transition strengths, such as the one-photon transition strength, but it involves a simultaneous absorption of two photons. This means that the negative two-photon transition strength is usually much weaker than the one-photon transition strength.

5. What are the applications of understanding the negative two-photon transition strength?

Understanding the negative two-photon transition strength is important in various fields, including quantum optics, nonlinear optics, and spectroscopy. It can be used to explain certain physical phenomena and to design and optimize devices such as lasers, sensors, and optical switches.

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