David J. Williams

Abstract: A powerful approach to the study of interfaces has been developing rapidly in the past decade. It is based on the spectroscopic methods of second-harmonic (SHG) and sum-frequency generation (SFG). These nonlinear optical techniques, being spectroscopic, provide information at the most fundamental level. A microscopic description of equilibrium and dynamic interface processes requires knowledge of the molecules at the interface, their orientational structure, the energetics that drive chemical and physical processes, and the time scale of molecular motions and relaxation processes. The techniques of second-harmonic and sum-frequency generation have made it possible to selectively probe the chemistry, physics, and biology of gas/liquid, liquid/liquid, liquid/solid, gas/solid, and solid/solid interfaces at the molecular level. In this abbreviated article only liquid interfaces will be considered; gas/solid and solid/solid interfaces are not included. This restriction is necessary because of the enormous increase in SH and SF studies in recent years, which makes it extremely difficult to properly discuss the range of work being carried out around the world. Unfortunately not all of the fine work even in the area of liquid interfaces has been included because of both space and time limitations. A number of review articles are referred to which cover some ofmore » the research material not covered in this article. 99 refs.« less

Abstract: The current state of materials development in nonlinear optics is summarized, and the promise of these materials is critically evaluated. Properties and important materials constants of current commercial materials and of new, promising, inorganic and organic molecular and polymeric materials with potential in second- and third-order nonlinear optical applications are presented.

Abstract: A two-state, four-orbital, independent electron analysis of the first optical molecular hyperpolarizability, β, leads to the prediction that |β| maximizes at a combination of donor and acceptor strengths for a given conjugated bridge. Molecular design strategies that focus on the energetic manipulations of the bridge states are proposed for the optimization of β. The limitations of molecular classes based on common bridge structures are highlighted and more promising candidates are described. Experimental results supporting the validity of this approach are presented.

Abstract: : A finite field method for the calculation of polarizabilities and hyperpolarizabilities is developed based on both an energy expansion and a dipole moment expansion. This procedure is implemented in the MOPAC semiempirical program. Values and components of the dipole moment (mu), polarizability (alpha), first hyperpolarizability (beta), and second hyperpolarizability (gamma) are calculated as an extension of the usual MOPAC run. Applications to benzene and substituted benzenes are shown as test cases utilizing both MNDO and AM1 Hamiltonians.

Abstract: We report the observation of second harmonic generation in a new class of organic polymeric materials, namely, electric field poled polymer glasses. Both the observed second harmonic coefficient (d33=6.0±1.3×10−9 esu, at 1.58 μm wavelength) and the poling process are described by a thermodynamic model that we have developed. The ability to form thin films from these materials may qualify them for integrated optics applications.