Nonlinear polarizabilities, molecular photonics

Optical second harmonic generation (SHG), which stems from the conversion of two photons of frequency to to a single photon of frequency 2(o, is an inherently surface-sensitive technique. Whereas no optical second harmonic wave is generated in the centrosymmetric bulk of a liquid, molecules participating in the asymmetry of the interface between two liquids (noncentrosymmetric environ-ment) contribute to SHG. Since the square root of SHG signal intensity, is proportional to the number N (per unit area), the molecular orientation (I) and the second order nonlinear polarizability of the SHG active species at the interface... 

The recent femtosecond experimental data on electron solvation in water (Gaudel et al., 1984, 1987) and observations in a mass spectroscopy on the formation of electrons stabilized in molecular beam clusters (Arbruster et al., 1984) has rekindled extensive interest on the microscopic details of the dynamics and structure of e in particular. Since the appearance of the visible spectrum of e has now been observed from the two photon photoionization of pure water (e.g., no dopant molecules or ions were present) we must focus on what responses can be Induced from the medium on this timescale. From our present databank, it is evident that following the instantaneous electronic polarizability (linear and nonlinear) response to the moving charge and/or field, it is the librational responses that must be the key motion. We assume, for the moment, that the lifetime of the autoionizing level in H2O is not a significant factor. As we have discussed elsewhere (Kenney-Wallace,... 

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