[ATM] Re: Fresnel lenses and correcting spherical abberation bycomputer.

[mdholm@telerama.com]

Actually, what you need to make a flat lens has already been done, and you can
buy such lenses commercially.  They have not yet been made of large enough size
and quality for most atm purposes, but there are specialized places where they
are just the ticket.  What are these little miracles?  What a lens really needs
to do is systematically change the phase delay of light over the lens aperture.
 You can do it with a material of uniform refractive index by varying the
thickness: a conventional lens.  You can also do it with a material of uniform
thickness by varying, you guessed it, the refractive index.  Enter the GRIN
(gradient index) lens.  As an example, look at Peter Ceravolo's home
interferometry setup.  He uses a GRIN lens to diverge the laser beam.  I don't
know why Peter chose a GRIN lens for that job, but he is a college trained
optical engineer, so I suspect he had a good reason.

Mark Holm
mdholm@telerama.com
_______________________________________________
ATM mailing list http://www.atmlist.net/