[ATM] grin optics for telescopes

[jess tauber <phonosemantics@earthlink.net>]

Hello again. Actually, I'm looking at optical plastics right now, not glass. As Bob May points out, there are inherent difficulties in creating large-scale glass with GRIN. Even so there are a number of methods utilized to make the glass units which can be carried over to plastics, which have some advantages in scaling up, as well as some disadvantages well known to people who deal with plastic lenses (for instance, easy to scratch, lack of resistance to UV in some cases (not great for space applications), etc.).

And I have some ideas I pulled out from biochemistry and other areas that appear never to have been tried before to add to the mix. A couple are cutting edge nanotech that probably need further development before ATM folks (or even major labs) can have at them.

A GRIN lens or corrector plate can be flat, and therefore very light in weight compared to an equivalent unit of uniform index of refraction throughout. Instead of depending on entry and exit surfaces the material within the lens/corrector varies (by density, chemical makeup, etc.)- light takes a continuous curving path inside the optical material.

So imagine if you will a catadioptric system consisting of an ultralight mirror, corrector, and tube- how big could you make this and still be able to carry it on your back? The notion of a GRIN corrector was put forward as long ago as the early 1970's by one of the pioneers in the GRIN field, Duncan T. Moore (now at U.Rochester) as part of his doctoral thesis (see D.T.Moore, "Catadioptric system with a gradient-index corrector plate," Journal of the Optical Society of America 67 (9), 1143-6 (1977)).

I spoke with Prof. Moore a couple of weeks ago- it seems I'm the first person to mention the idea to him in at least 25 years. Maybe some of my ideas will solve the problems of making large GRIN optics (which I like to refer to as either RBG (really big GRIN), or more jokingly, "SMILE". Maybe not. Only experimentation will tell- I'm hoping to get some lab time at my local college this summer, and Peter Chen has been very enthusiastic about the possibilities in correspondence.

In the meantime I'm collecting as much information as I can about the different optical plastics, their properties, and the properties of their chemical precursors, since it is the latter that will ultimately make or break this endeavor.

Giant refractors are also made feasible with big GRIN lenses- people are already planning on using Fresnel lenses (yes- actual image-producing ones!) this way in space telescopes. They've already got proof-of-concept units out several feet wide, and foldable to boot. But Fresnel lenses have all sorts of diffractive nonsense going on that need to be secondarily corrected that GRIN optics wouldn't be heir to. I don't know about chromatic aberration in GRIN- haven't got that far in my reading (I'm still playing catch-up).

It was actually this very ATM list that got me started down this road. I'd been out of astronomy as a teenage hobbyist for decades, and blundered my way into getting a junko Chinese-made reflector for my nephews for Christmas, thinking that it was equivalent to the one I had from the early 70's.  Crappy optics, easily snapped fittings and mount pieces got me reading product reviews on the WWW. Several quantum jumps later, and I'm already deep into aperture fever. Pretty rapid evolution towards do-it-yourself leads me here, and perusal of the archives, Dr. Chen's work, a visit to the Stellafane site, etc.

My own experience is in the chemical field- various areas including natural product extraction and purification, adhesives R&D, analytical work (believe it or not my primary focus these days, if you'll pardon the pun, is work on developing linguistic materials to help save an endangered South American Indian language from extinction).

So anyway, this is all pretty new to me too, and there are no guarentees- wiser heads thought about all this decades ago and walked away. But you never know, sometimes the less traveled roads turn out to be the correct ones.

Thanks for the comments so far- keep 'em coming!

Jess Tauber
phonosemantics@earthlink.net




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