... Imaging GRIN Rod Lens (HAG's) | Relay Rod Lens (LAG's) | ... The Refractive Index Distributions (RID) in GRIN lens preforms are made by multi-stage optimized ion-exchange diffusion between silicate mineral glasses and salt melts. ... In the LAG lenses - L ow A perture GRIN the nature of the changing of refractive index in glass via ion-exchange lies mainly in molecular volume increase. ... LAG lenses are specially treated to create the dark anti-flick surface coating (Fig.2). ...