Editing Gradient-index optics (section)

== Manufacture ==
GRIN lenses are made by several techniques:
* [[Neutron]] irradiation – [[Boron]]-rich glass is bombarded with neutrons to cause a change in the boron concentration, and thus the refractive index of the lens.<ref name=moore /><ref>Sinai P, (1970). ''Applied Optics''. 10, 99-104</ref>
* [[Chemical vapour deposition]] – Involving the deposition of different glass with varying refractive indexes, onto a surface to produce a cumulative refractive change.<ref name=moore /><ref>Keck D B and Olshansky R, "Optical Waveguide Having Optimal Index Gradient," U.S. Patent 3,904,268 (9 Sept. 1975).</ref>
* Partial [[polymerisation]] – An organic [[monomer]] is partially polymerized using [[ultraviolet light]] at varying intensities to give a refractive gradient.<ref name=moore /><ref>Moore R S, "Plastic Optical Element Having Refractive Index Gradient," U.S. Patent 3,718,383 (Feb. 1973).</ref>
* [[Ion exchange]] – Glass is immersed into a liquid melt with [[lithium]] ions. As a result of [[diffusion]], [[sodium]] ions in the glass are partially exchanged with lithium ones, with a larger amount of exchange occurring at the edge. Thus the sample obtains a gradient material structure and a corresponding gradient of the refractive index.<ref name=moore /><ref>Hensler J R, "Method of Producing a Refractive Index Gradient in Glass," U.S. Patent 3,873,408 (25 Mar. 1975).</ref>
* Ion stuffing – [[Phase (matter)|Phase]] separation of a specific glass causes pores to form, which can later be filled using a variety of [[Salt (chemistry)|salt]]s or concentration of salts to give a varying gradient.<ref name=moore /><ref>{{cite book |last1=Mohr |first1=R K |last2=Wilder  |first2=J A |last3=Macedo |first3=P B |last4=Gupta |first4=P K |date=1979 |chapter=Graded index lenses by the molecular stuffing process |title=A digest of technical papers presented at the Topical Meeting on Gradient Index Optical Imaging Systems, May&nbsp;15-16, 1979, Rochester, New York |others=paper WA1 |location=Washington, D&nbsp;C |publisher=Optical Society of America |pages= |oclc=489755284}}</ref>
* [[Direct laser writing]] – While point-by-point exposing the pre-designed structure an exposure dose is varied (scanning speed, laser power, etc.). This corresponds to spatially tunable monomer-to-polymer degree-of-conversion resulting to a different refractive index. The method is applicable to free-form micro-optical elements and multi-component optics.<ref>{{cite journal|last1=Zukauskas|first1=Albertas|last2=Matulaitiene|first2=Ieva|last3=Paipulas|first3=Domas|last4=Niaura|first4=Gedinimas|last5=Malinauskas|first5=Mangirdas|last6=Gadonas|first6=Roaldas|title=Tuning the refractive index in 3D direct laser writing lithography: towards GRIN microoptics|journal=Laser & Photonics Reviews|date=2015|volume=9|issue=6|pages=706–712|doi=10.1002/lpor.201500170|bibcode=2015LPRv....9..706Z}}</ref>