Knoop and Vickers hardness, Young's Modulus, and fracture toughness measurements were performed on Corning's Code 9575 calcium fluoride in various orientations. Other commercially available sources of calcium fluoride were also measured for comparison of properties. Knoop hardness and elastic properties exhibited a dependence on orientation while no such dependence was observed for Vickers hardness and fracture toughness. The results also indicated that these physical properties were not dependent on the source of the material
In large fused silica blanks, typically greater than 225mm in diameter and 40mm thick, recent glass forming improvements have improved the homogeneity in Corning HPFS fused silica by 51%. Overall homogeneity peak to valley values improved from an average 1.4ppm to 0.69ppm. This paper describes the experimental results on homogeneity and birefringence resulting from these Forming improvements.
As optical lithographers push to extend optical lithography technologies to create smaller features with higher NA, lower k1 values and shorter wavelengths, transmitted wavefront specifications for HPFSR fused silica blanks continue to tighten. HPFSR fused silica blanks are typically certified for acceptance using an interferometer operating at a wavelength of 632.8 nm. As the market demands increasingly tighter homogeneity specifications, it has become critical to understand the sources of variation in wavefront measurements. Corning has recently initiated a study to identify those sources of variation. One glass attribute being studied is the impact of residual stress on the wavefront. It is known that residual stresses can alter the refractive index of fused silica. To obtain the residual stress measurements, birefringence measurements were obtained at 632.8 nm for comparison to wavefront measurements at 632.8 nm. The relationship between residual birefringence and transmitted wavefront measurements, at 632.8 nm on Corning HPFSR fused silica blanks, is explored in this paper.
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