Second harmonic generation by charge-transfer excitons interacting with phonons

Effects of exciton-phonon interaction on the nonlinear optical response of charge-transfer excitons (CTE) are studied in the framework of an exactly solvable model. It is found that the second order excitonic optical polarizability beta is modified due to the CTE-phonon interaction. For a nonresonant frequency range, where beta is relatively small, the change is not significant. On the contrary, in the vicinity of resonances (when the Light frequency omega approximate to omega (0) or omega approximate to omega (0)/2, omega (0) is the CTE transition frequency), the CTE-phonon interaction may remark ably diminish the value of beta. This should be taken into account when considering CTE systems in nonlinear optics.