MICROSCOPIC CALCULATION OF THE 3RD-ORDER NONLINEAR-OPTICAL SUSCEPTIBILITY OF DEANST CRYSTAL

The linear and nonlinear optical response properties of crystalline DE ANST, N,N-diethyl-4-(2-nitroethenyl) phenylamine, have been computed r igorously, using a large set of input data including modified neglect of differential overlap (MNDO) and nb initio theoretical estimates of molecular polarizability alpha and hyperpolarizabilities beta and gamm a, and experimentally measured refractive indices. The currently avail able microscopic expression for the third-order susceptibility tensor chi((3)) of a molecular crystal has been corrected to include all poss ible frequency combinations in the cascading term. Calculations of lin ear response based on theoretical polarizabilities alpha fail to repro duce the experimental refractive indices of the crystal, and hence an effective polarizability tensor has been derived from the measured ref ractive indices and used in the computation of the local electric fiel d. The calculation of chi((3)) based on the MNDO hyperpolarizabilities is in tolerable agreement with the experimental measurements of third -harmonic generation. Environmental effects on the molecular response play a key role in the accuracy of the calculation. (C) 1997 American Institute of Physics.