An axial gradient-index (GRIN) lens, where the refractive index varies along the optical axis of a convex lens, can reduce the spherical aberration compared with the conventional homogeneous lens. The transparent plastic axial GRIN material was successfully fabricated by chemical copolymerization and diffusion techniques. The depth of the gradient index was ~20 mm with the refractive-index change Δn = 0.07. By carrying out the ray tracing of the axial gradient index, the optimum refractive-index distribution reducing the spherical aberration was determined. If we assume that the axial GRIN lens was constructed from the sample experimentally obtained, it was theoretically confirmed that the spherical aberration of this lens would be remarkably improved.
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