DISPERSION FORMULAS FOR THE 2ND HYPERPOLARIZABILITY COMPONENTS GAMMA(PARALLEL-TO), GAMMA(PERPENDICULAR-TO) AND GAMMA(K)

The frequency-dependence of the isotropic parallel average gamma(paral lel to) of the second hyperpolarizability can be expanded in a compact way using dispersion coefficients, which are independent of the optic al process, if three effective frequencies are introduced. We propose similar expansions for the second hyperpolarizability components gamma (perpendicular to) and gamma(K) and give explicit expressions for the hyperpolarizability dispersion coefficients in terms of the derivative s of the hyperpolarizabilities with respect to their frequency argumen ts. The relation of the hyperpolarizability dispersion coefficients to the Cauchy moments of linear response theory is discussed and compari son is made with previously proposed dispersion formulas. (C) 1998 Els evier Science B.V. All rights reserved.