Navegando por Autor "Hench, L. L."
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Item Gel-silica optics : theory and application.(1994) Hench, L. L.; Araújo, Fernando Gabriel da Silva; West, J. K.; La Torre, J. P.A new generation of silica optics has resulted from alkoxide-based sol-gel processing of silica including: net shape transmissive optical elements, surface diffractive optics, inorganic doped GRIN optics, organic impregnated optical composites such as dye lasers and scintillators, optics with internal diffraction gratings, laser densified microoptical lenses and arrays, and laser densified waveguides. Processing control of the ultrastructure of the monolith at the time of gelation and during aging is essential to producing the optical devices together with chemical and thermal stabilization of the surface of the pore network prior to densification or impregnation. The process control variables for gel-silica optics are summarized together with spectroscopic analysis and molecular orbital calculations that explain how and why the thermal-chemical processing controls work at a molecular level.Item Laser densification of channel waveguides in gel-silica substrates.(1994) Araujo, Fernando Gabriel da Silva; Chia, T.; Hench, L. L.Channel waveguides are important components in optical signal processing. A new method is described for producing such waveguides with high design flexibility. The channel waveguides are produced using CO2 laser densification of partially densified gel-silica matrices (Type VI optical silica). Critical processing conditions include pore size and initial density of the matrix, laser power, translational speed of the sample, distance between sample and focusing lens, and ambient humidity. Channel waveguides less than 500 #m wide were produced in gel-silica substrates of different pore sizes and bulk densities through laser densification. Optically transparent waveguides were obtained for speeds of the sample over 1.4 cm/s and laser power settings ranging between 12 and 16 mA. Substrates with three different pore sizes were analyzed, i.e, 12, 30 and 45/~, with densities varying from 1.1 g/cc to 2.1 g/cc. Fourier transform infrared microspectrometry of the densified regions showed that IR shifts ranging from 1 to 38 cm- 1 in the peak position of the Si-O-Si stretching vibrational mode were achieved. This corresponds to changes of index of refraction ranging from 0.01 to 0.20. The experiments show also that the larger the pore size the wider is the range of parameters for producing effective waveguides.Item Structural evolution of a porous type-VI sol-gel silica glass(1995) Araújo, Fernando Gabriel da Silva; LaTorre, G. P.; Hench, L. L.The structural evolution of type-VI porous sol-gel-derived optical glasses is described. The average pore radius of the glasses studied is 30 ,A, with an exceptionally narrow pore size distribution. These glasses are particularly suited to laser surface densification. Their properties make them also attractive as matrices for impregnation of second phases and as a substrate material for the production of fully dense optical lens elements and micro-optical devices. The properties of the matrices are reported for the as-dried state to densities approaching 2.2 g/cm 3, with thermal treatments from room temperature to 1060°C. The parameters of sintering for the gel-glass transformation are measured, and the phenomena occurring for three temperature ranges are evaluated. An activation energy of 65 + 9 kcal/mol for sintering with a structure factor n = 1.0 + 0.3 was found for the initial stage sintering of the material.