Gradient-index rod lens made by a double ion-exchange process.

Gradient-index rod lenses with a parabolic-index profile have been fabricated by a double Na-Ag ion-exchange process, and their optical characteristics have been evaluated. The numerical aperture and minimum focused spot diameter of the 2-mm diam rod lens were 0.58 and 2.5 microm for lambda = 0.63 microm, respectively. Because of the high diffusing rate for Ag ions, this technique offers the possibility of making large-sized (larger than 10 mm-diam) rod lenses for photographic uses.