Damping corrections and the calculation of optical nonlinearities in organic molecules

Damping, the effects of uncertainty, Doppler, collisional, and other mechanisms that lead to the broadening of electronic transitions are rarely accounted for in the calculation of optical nonlinearities. Using the two-level model as an illustration, this work points out that damping corrections can be substantial for organic compounds, even for two- or three-photon resonances, and that these corrections are dependent on molecular symmetry. Comparisons of calculated and measured susceptibilities need to take this into account. Results are presented for the quadratic electro-optic, third-harmonic, and electric-field-induced second-harmonic-generation processes.