Two-level TPA model

Two-Level Model A two-level model can appropriately describe TPA under resonant conditions if the molecule bears a dipolar substitution pattern. A repre-... 

Fig. 2 Schematic representation of the TPA process, (a) In the case of the three-level model for symmetric systems (b) in the case of the two-level model for noncentrosym-metric systems...

If no transition is allowed between the high-lying electronic states A3 and A5, the limiting action although slightly better than a pure two-photon transition model, does not compare with the complete model which clamps the output at a very low level (see Fig. 12.32). Accordingly, materials possessing both TPA and ESA properties... 

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