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refractory
Pooh-Bah
Reged: 02/05/05
Posts: 1233
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I'm curious to know. If materials have a particular refractive index, will it also have to maintain particular thicknesses in order to properly interact with light of different wavelengths? What if the material is uniformly flat, and thinner than any wavelength of light passing through?
Jess Tauber
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John Carruthers
Skiprat
Reged: 02/02/07
Posts: 2270
Loc: Kent, UK
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think of an etalon, material of thickness 'any integer of 1/2 wavelengths' will interact with the light passing through. A solid monchromator is also designed around this principle but I don't know of any material thinner than a wavelength of visible light except AR or filter coatings for instance which have a substrate to support them.
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Jc
ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light )
6" F7 spec
127mm F9.4 Refractor
10 x 50 bin
ETX80 (finder)
Canon 20D
PST
DSI 1
and a curious mind
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4940
Loc: MA
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If you want an optical element that bends light (a prism), or with optical power (a lens), then the two surfaces can not be parallel. Simple geometry and Snell's law constrains how thin the element can be.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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refractory
Pooh-Bah
Reged: 02/05/05
Posts: 1233
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Graphene is supposed to have a refractive index, even with visible wavelengths, yet is one atom thick. How does THAT work?
Jess Tauber
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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As a wild guess, I'd say it's because light travels slower through the material than it does through a vacuum. Just a guess. 
OTOH light travels slower through everything (that it travels through) than it does through a vacuum...
Still, you want to know how a one-atom thick material, a mere hundredth of a wavelength or less, can bend light, right? It's the interaction of the EMF with the electrical field of the atoms that does it. One atom or a billion, I don't think it matters. The electrical field in or near an atom is sticky to the light wave, in a sense. The classical image is the squadron of soldiers marching in step and hitting a muddy field at an angle - gradually they all turn a bit.
It's probably the mean-free-path for the photons at work (another way to think about it), the way that you can trap light in the right material and slow it down to a fast walk - these materials look like fog, but the light goes in one side and comes out the other considerably later.
Best,
Mark
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refractory
Pooh-Bah
Reged: 02/05/05
Posts: 1233
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So let's say we coat the graphene with another single-atom-thick layer of a mixture of compounds that have, in their unmixed states, distinct refractive indexes. And that we create a component gradient radially so that the refractive index grades radially.
We then do the same thing on the other side of the graphene, but with a slightly different gradient of the same, or other materials with different RI's.
Would this then amount to a three-molecule or atom thick gradient index lens capable of focusing light?
Jess Tauber
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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What Luigi said, not a lens if it's parallel, no matter the index(es). A GRIN lens works (divergent around an axis) because it has a variation in index of refraction as you go away from the center line of the lens.
Best,
Mark
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refractory
Pooh-Bah
Reged: 02/05/05
Posts: 1233
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Yes- I understand this- that is why I specified that the two layers of coated material on each side of the graphene have DIFFERENT radial gradients of RI, so it has both radial and linear gradients. The question here is whether this can still bring light to focus due to the thinness of the material, not the RI gradients.
I would imagine that such a lens, IF it worked, would have a very long focal length.
Jess Tauber
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Sorry, I misread your post. 
How do you make the radial gradient out of material that shares the same atomic configuration, then? If you could do that, sure, it's a lens, albeit a very very long focus length one. The thickness doesn't matter, like I said.
Best,
Mark
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refractory
Pooh-Bah
Reged: 02/05/05
Posts: 1233
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Companies now offer all sorts of mineral nanoparticles, including diamond(oid). A whole range of different RI's. If they can be melted or bonded in situ after mixing one might be able to finely control the overall radial gradient. Would be thicker than one molecule, though. There are other ways- various ions with different RI's could be sprayed on with the mix varying with radius.
Jess Tauber
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Now you're introducing all kinds of stacking and layering issues, unless it's intended to be some sort of glass. The "If" in the third sentence is huge.
Best,
Mark
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