A gradient-index element is one in which the refractive index varies appreciably in a layer just below the surface of the glass. The present paper deals with practical methods of tracing rays through such a medium. One method, due to L. Montagnino, lends itself to rapid computer ray tracing. A second method, through restricted to the case of spherical symmetry in the index function, lends itself both to computer tracing and to analytical investigations.
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