Microscopic theory of molecular crystal surface second-harmonic generation

R. W. Munn

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Second-harmonic generation (SHG) is induced in molecular crystals by the variation through the surface region of the electric fields associated with the optical wave and with the permanent electric multipole moments of the molecules. It arises from the molecular first hyperpolarizability, whether permanent or induced by electric fields at noncentrosymmetric sites in the bulk crystal or at sites in the surface region where centrosymmetry is lost. Algebraic expressions suitable for iterative numerical evaluation are derived for the molecular response coefficients as affected by the multipole fields in the surface region. Detailed expressions are then derived for the surface second-harmonic generation in terms of the spatially varying molecular response and a microscopic expression that is derived for the variation of optical electric field through the surface region. The treatment does not require the introduction of a surface dielectric constant but incidentally yields a microscopic expression for it. The quadratic susceptibilities for surface SHG in anthracene and pyrene are roughly estimated as respectively 1/80 and 1/20 that in p-nitroaniline, reported to be 4 fm V-1; the coefficients could vary by one or two orders of magnitude among different surfaces.

    Original languageEnglish
    Pages (from-to)850-859
    Number of pages10
    JournalThe Journal of chemical physics
    Volume103
    Issue number2
    Publication statusPublished - 1995

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