Gradient-index lenses for near-ideal imaging and concentration with realistic materials

Gradient-index lenses for near-ideal imaging and concentration with realistic materials: "Panagiotis Kotsidas, Vijay Modi, Jeffrey M. Gordon
Fundamentally new classes of spherical gradient-index lenses with imaging and concentration properties that approach the fundamental limits are derived. These analytic solutions admit severely constrained maximum and minimum refractive indices commensurate with existing manufacturable materials, ... [Opt. Express 19, 15584-15595 (2011)]"