Research Initiation Award: Nonlinear Optical Materials Via Sol-Gel Processing

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The discovery of optical second harmonic generation in crystals in 1961 spurred rapid progress in the field of nonlinear optics. Nonlinear optical materials are materials whose optical properties depend upon the intensity of light incident upon them. The nonlinearity could be in the form of an intensity dependent refractive index or a saturable absorption. These materials have practical applications in telecommunications, digital computers, and laser fusion. They have the potential to become future optical semiconductors which can operate at frequencies two to three orders of magnitude higher than current semiconductor technology. The PI plans to explore formation of commercially viable nonlinear optical materials using the sol-gel technique. The sol-gel process is a means for producing inorganic films and monolithic structures from organo-metallic monomeric compounds. The process is analogous to step reaction polymerizations in organic systems where the monomer is usually a metal alkoxide such as tetramethoxysilane. These reactions are run at room temperature, in a common solvent for alkoxide and water, and using either an acid or base catalyst. The sol-gel process will be used to produce new nonlinear optical materials by polymerizing modified alkoxide monomers of the form RSi(OR')3 where R represents an organic functionality demonstrated to have a high nonlinear susceptibility. Work will focus on R-groups which are primarily substituted benzenes, pyridines and azo dyes. Commercially available alkoxides and custom alkoxides synthesized as part of this research will be investigated. Thin film and monolithic materials will be made. To facilitate the observation of second-order nonlinear effects, the dipoles of the organic functionality will be aligned using corona poling. The second-order and third-order susceptibilities of the starting materials as well as the polymerized materials will be assessed using second harmonic generation and four-wave mixing respectively. The strength, chemical and environmental resistances, and thermal stability of the film and bulk materials will also be determined.