Abstracts

There has been much recent interest in thedevelopment of nonlinear optical composite materials as they canposses large values of the nonlinear susceptibility. A nonlinearoptical composite material is capable of enhancing the nonlinearresponse of its component materials due to the nonuniform electricfield distribution between the constituents. For this reason theeffective bulk nonlinear optical susceptibility is not typicallygiven by the volume weighted average of the individualsusceptibilities. It is the goal of the present work to investigatethe enhancement effect of second-order and third-order nonlinearoptical composite materials as well as third-order photonic bandgap materials and also to consider the accuracy of nonlineareffective medium theory.
Layered opticalcomposite materials can enhance the nonlinear susceptibility forelectric fields polarized normal to the plane of the layers. Forenhancement to occur, the dominant nonlinear constituent mustposses an optical dielectric constant lower than that of the otherconstituent. This is the usual condition for enhancement for allcomposite geometries. As a test of consistency of the nonlineareffective medium theory, predictions were compared against theresults of the well accepted formalism for calculatingsecond-harmonic generation in multilayer materials. In thecalculations performed, the effective medium predictions were inconsistent agreement with the more exact formalism. Also athird-order electrooptic layered composite material was constructedand the third-order susceptibility was measured for both thecomposite material and a homogeneous film of the nonlinear dominantmaterial. The composite susceptibility was measured to be 3.2 timesthe susceptibility of the homogeneous material, in reasonableagreement with the predictions of effective medium theory.
In a digression from the optical compositematerials mentioned above, another type of two-component materialwas studied for its ability to enhance the nonlinear opticalresponse of a given homogeneous material. One-dimensional photonicband gap structures were analyzed for their ability to enhance thethird-order response of their constituents. It was found that thethird-order response of either a high refractive index or a lowrefractive index constituent could be enhanced near the photonicband edge of the band gap material. Typical enhancement factorswere in the range of 4-6. Introduction of a central "defect"nonlinear region into the middle of the photonic band gap materialresulted in an enhancement factor of approximately 30 over anequivalent length of homogeneous nonlinear material.
Finally the effective third-order nonlinearsusceptibility of a Maxwell Garnett optical composite wascalculated for a composite material with a nonlinear host mediumand the spherical inclusions arranged on a simple cubic lattice.This allowed for a calculation that was accurate for all fillfractions up the close pack limit unlike previous treatments ofsuch composites