Nonlinear optical response of charge-transfer excitons at donor-acceptor interface

5 Nonlinear optical response of charge-transfer excitons at donor—acceptor interface 

1 Resonant optical nonlinearity of CTEs the role of the exciton-exciton 

We have already discussed some peculiarities of the exciton-exciton interaction at a D-A interface above. Nevertheless, for the convenience of the readers we repeat here some results of this discussion to also make this section self-contained. 

Assuming that the mean distance between CTEs p 10 a, e.g. that the concentration of CTEs is of the order of 10 2 we obtain that Ae 150 cm-1, which is significant on the scale of the homogeneous width of a CTE transition. 

As discussed above, the scaling dependence Ae n3/2 follows also from the results of numerical simulations and, thus, the estimate made is expected to be valid even for a disordered homogeneous distribution of CTEs of comparable 2D density n. We wish to stress here the nonanalytic dependence of Ae on n a perturbation theory expansion in terms of n, n2, n3, etc. would be inadequate as the leading correction scales like n3/2. 

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