The concept of isoindicial surfaces and position variables is used to develop analytical expressions for the effective focal length and back focal length of a single gradient lens with a spherical distribution of refractive index, where the square of the refractive index is a quadratic function of the distance from the center of symmetry.
© 1992 Optical Society of America
Sead Dorić and Nathalie Renaud, "Analytical expressions for the paraxial parameters of a single lens with a spherical distribution of refractive index," Appl. Opt. 31, 5197-5200 (1992)