Molecular Materials for Nonlinear Optics
RICHARD S. POTEMBER, ROBERT C. HOFFMAN, KAREN A. STETYICK, ROBERT A. MURPHY, and KENNETH R. SPECK MOLECULAR MATERIALS FOR NONLINEAR OPTICS An overview of our recent advances in the investigation of molecular materials for nonlinear optical applications is presented. Applications of these materials include optically bistable devices, optical limiters, and harmonic generators. INTRODUCTION of potentially important optical qualities and capabilities Organic molecular materials are a class of materials such as optical bistability, optical threshold switching, in which the organic molecules retain their geometry and photoconductivity, harmonic generation, optical para physical properties when crystallization takes place. metric oscillation, and electro-optic modulation. A sam Changes occur in the physical properties of individual ple of various applications for several optical materials molecules during crystallization, but they are small com is shown in Table 1. pared with those that occur in ionic or metallic solids. The optical effects so far observed in many organic The energies binding the individual molecules together materials result from the interaction of light with bulk in organic solids are also relatively small, making organic materials such as solutions, single crystals, polycrystal molecular solids mere aggregations of molecules held to line fIlms, and amorphous compositions. In these materi gether by weak intermolecular (van der Waals) forces . als, each molecule in the solid responds identically, so The crystalline structure of most organic molecular solids that the response of the bulk material is the sum of the is more complex than that of most metals or inorganic responses of the individual molecules. That effect sug solids; 1 the asymmetry of most organic molecules makes gests that it may be possible to store and process optical the intermolecular forces highly anisotropic.
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