Solid matrix Christiansen filters.

Abstract

Christiansen filters are scattering filters composed of two materials with dispersion curves (for refractive index) that intersect at one wavelength. These filters transmit unscattered light at the intersection wavelength and incoherently scatter light of other wavelengths. Unlike filters based on optical interference, the transmitted wavelength does not depend on the angle of light incidence on the filter. These filters have been fabricated with solid host matrices by mixing finely ground optical glass powders with pellets of optical grade resins and injection molding the combination into planar filters of various sizes. This method of fabrication can produce filters of any shape or size, limited only by the skill of the mold designer and the size of the molding machine. This dissertation discusses the fabrication, characterization and modeling of solid matrix Christiansen filters. After a brief proposal of our research objectives to motivate this study, the concepts behind and history of these filters are reviewed. A multiple scattering theory of Christiansen filters is discussed and a computer-based search for compatible materials is summarized. After verifying the refractive index dispersions of the selected polymer matrices, a detailed description of the technology and fabrication of these filters follows. Spectral transmission and other measurements are employed to characterize the optical performance of the filters and to compare the filters to theoretical models. We have produced blue, bandpass filters with transmittances ranging from 0.25 to 0.40 at 392 nm; green, bandpass filters with transmittances of 0.20 centered at 510 nm; and near-infrared, edge filters which begin at 700 nm and reach maximum transmittances ranging from 0.30 to 0.50 at 800 nm. The dissertation concludes with recommendations for future improvements and suggestions for possible applications. The results from the computer-based material search and tables of fabrication parameters are included in two appendices.