Refractive index and dispersion variation in precision optical glass molding by computed tomography

Glass compression molding is an alternative manufacturing method for efficient, high-quality, low-cost optical component manufacturing. However, in compression molding, refractive index variation is inadvertently introduced to glass, which can influence optical performance of molded glass lenses, especially for lenses used in high precision applications. In order to study refractive index variation and dispersion in molded glass lenses after cooling, a group of BK7 cylindrical glass lenses were thermally treated with various heating and cooling conditions. The molded glass lenses were measured by use of an optical setup based on a Mach-Zehnder interferometer with red, green, and blue lasers separately. Using the wavefront information extracted from fringe patterns, refractive index and dispersion variation in molded glass lenses were reconstructed using a filtered backprojection algorithm. Furthermore, refractive index and dispersion variation at different cooling rates and different soaking temperatures were investigated.