Radial gradient index (GRIN) lenses have a refractive index profile which varies radially outward from the optical axis. High numerical aperture GRIN lenses use glasses containing thallium oxide. The refractive index gradient is produced by ion exchange of potassium, K + , from a molten salt bath, for thallium, TI + , in the glass. Thallium is highly toxic, making its use prohibitive in a manufacturing environment in the United States. Of the single valent ions, only silver and thal;Iium provide a large enough index change to produce high numerical aperture GRIN lenses when exchanged with alkali ions. Gradient Lens Corp. is using a silver containing glass and exchange of sodium for silver to produce the gradient. This work addresses the problem of optimizing the composition of a silver containing glass for ion exchange. The glass must have relatively high ionic mobility, be chemically resistant to the salt bath, and produce a good refractive index profile to provide high quality imaging. A series of silver containing glasses is being melted and their conductivity and c@mical resistance measured. Ion exchange experiments will be performed in the successful candidate glasses and the refractive index profile will be measured and analyzed.The potential commercial application as described by the awardee: Higher numerical aperture GRIN rod lenses made by silver ion exchange processes will be directly competitive with thallium-based GRIN rods produced in Japan. Applications include copier arrays, endoscopes, borescopes, optical fiber couplers, collimators, and focusing optics.
