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#1 boothg599

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Posted 11 June 2021 - 02:59 AM

What do y'all think about a project using these things? https://www.nature.c...467-021-23358-8

#2 luxo II

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Posted 11 June 2021 - 03:56 AM

That is so packed with buzzwords it was probably writtten by a buzzprose generator.

Anyway that definition of “spaceplate” is satisfied by solid glass - a solid optic could be 30% shorter than one full of air. Only snag is the weight.

Think I’ll file the at one in the round file, along with cold fusion and the mysterious fictitious magical “quantum telescope”
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#3 Gleb1964

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Posted 11 June 2021 - 06:00 AM


 

Anyway that definition of “spaceplate” is satisfied by solid glass - a solid optic could be 30% shorter than one full of air.s magical “quantum telescope”

No, it is opposite to that - solid glass instead of air space would slow beam convergence and take 50% more space.
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#4 MitchAlsup

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Posted 11 June 2021 - 03:51 PM

What kind of Eyepieces will we need to use at F/0.5 primaries ?


Edited by MitchAlsup, 11 June 2021 - 03:51 PM.


#5 jimhoward999

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Posted 11 June 2021 - 09:21 PM

If you put a plate of glass in an optical train it stretches the path by t(n-1)/n where t is the thickness of the plate.  To get compression of the path with a plate you need a negative index of refraction.  

 

Negative index materials have been theorized using "meta-materials"  and demonstrated in the microwave region.  But I don't think negative index meta-materials have ever been created in the optical domain. 

 

The authors of the article present some ideas on "spaceplate" materials they think might work.  I think these are just hypothetical ways to get at an optical meta-material with a negative index....they must be because that is the only way you get compression with a zero-power plate.  I am certainly not smart enough to analyze the presented concepts, which were difficult to follow.  But they seemed pretty fishy.



#6 TOMDEY

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Posted 12 June 2021 - 09:18 AM

It's mumbo-jumbo. Would take a nondispersive index of refraction of a thousand to even begin to get something that has a prayer of slightly working. Complete baloney.    Tom



#7 Gleb1964

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Posted 12 June 2021 - 09:27 AM

If you put a plate of glass in an optical train it stretches the path by t(n-1)/n where t is the thickness of the plate.  To get compression of the path with a plate you need a negative index of refraction.

Yes, that is correct formula.
So, to shrink the space you would need refraction index between 0 and 1. Why are you talking negative index? See in article used "a negative uniaxial birefringent medium", not a negative.



#8 MKV

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Posted 12 June 2021 - 11:05 AM

It's mumbo-jumbo. Would take a nondispersive index of refraction of a thousand to even begin to get something that has a prayer of slightly working. Complete baloney.    Tom

Lol, personally, I'm waiting for deferents and epicycles to enter the stage...it worked the last time they were introduced.  :o)

 

 

So, to shrink the space you would need refraction index between 0 and 1. 

How can a refractive index of a "medium" be less then unity, Gleb? Vacuum refractive index is 1. What's "medium" would it take to have one?

 

But, today, many things are "possible" and "real" if  you can just imagine it. :o)  

 

According to researchgate,

 

https://www.research...this-phenomenon

 

refractive index can not only have a value of less than 1 but it can also be negative! It's sort of like the geometric raytrace result of a paraboloidal mirror on-axis -- the image is a dimensionless dot. Sure. It may even depend on what day of the week it is. :o)

 

popcorn.gif



#9 Gleb1964

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Posted 12 June 2021 - 12:09 PM

How can a refractive index of a "medium" be less then unity, Gleb? Vacuum refractive index is 1. What's "medium" would it take to have one?

 

Mladen

 

Refraction index is related to phase velocity which can by any. If refracting index less then 1, phase velocity is above speed of light. That what is happened within absorption bands, for example. 

 

about phase velocity.jpg



#10 jimhoward999

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Posted 12 June 2021 - 12:58 PM

Yes, that is correct formula.
So, to shrink the space you would need refraction index between 0 and 1. Why are you talking negative index? See in article used "a negative uniaxial birefringent medium", not a negative.

yes you are right....brain fart on my part.  A negative index meta-material would actually increase the space even more than a plate of regular glass. 



#11 jimhoward999

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Posted 12 June 2021 - 01:49 PM

Here is a spaceplate configuration that does work...sort of

Slide2.JPG

 

You put a beamsplitter coating on both sides of a plate parallel plate and let the light bounce back and forth.  Of course the throughput with 4 bounces is only 1.5% and the remaining 98% of the light lives in horrible ghost images, but it still probably works as well as the hypothetical electro-optical devices in the paper.

 

You could also tilt the surfaces at 45° to regain the throughput

 

Slide3.JPG

 

oh look I've invented the Porro prism.

 

The point is there are conventional ways to shorten an optical system if you are willing to add components.


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#12 MKV

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Posted 12 June 2021 - 06:37 PM

Refraction index is related to phase velocity which can by any. If refracting index less then 1, phase velocity is above speed of light. That what is happened within absorption bands, for example. 

I guess it all depends how how one defines it mathematically. When I was in school, refrective index = n/n'. All my optical programs still treat it that way.  



#13 luxo II

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Posted 13 June 2021 - 12:03 AM

And there are these funny things called mirrors. Notably concave and convex ones. I have a scope with a 3m focal length packed into an 80cm OTA. 

 

that qualifies, according to the definition. 


Edited by luxo II, 13 June 2021 - 12:05 AM.


#14 freestar8n

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Posted 13 June 2021 - 02:54 AM

For people interested in related topics, here is a nice summary of the long history of work in metamaterials:

 

https://engineering....2007/Part-3.pdf

 

And here is the upcoming program on metamaterials for the SPIE conference on optics and photonics:

 

https://spie.org/OPN...ces-metasystems

 

To learn more about the feasibility of refractive index < 1 you can read up on the Drude model of metals, well over 100 years old - keeping mind that "n" is a complex number.

 

Frank



#15 freestar8n

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Posted 13 June 2021 - 02:59 AM

The OP has made their first posting with this topic - so - welcome to CN.

 

What is your opinion of the article?

 

Frank



#16 Gleb1964

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Posted 13 June 2021 - 07:38 AM

It's mumbo-jumbo.

Tom.

I have a similar filling until I can see real working examples. But I am not an expert in the area to immediately dismiss it. I think, there are special application where physics can be formally described in a such math terms.
 

I guess it all depends how how one defines it mathematically. When I was in school, refrective index = n/n'. All my optical programs still treat it that way.

Mladen,
 
refractive index is a relation between phase speed in vacuum and in media. Phase speed above speed of light is reality. The only group speed is limited to the speed of light, that is the speed of energy (information) propagation.
Ray tracing optical software is based on phase calculation. Using of negative refraction index for mirrors in software should not be confused with media negative index, meaning phase propagation in the opposite direction to the group speed.

Here is illustration of phase speed faster than group speed: https://www.youtube....h?v=tlM9vq-bepA
 



#17 MKV

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Posted 13 June 2021 - 10:10 AM

Mladen,

refractive index is a relation between phase speed in vacuum and in media. Phase speed above speed of light is reality. The only group speed is limited to the speed of light, that is the speed of energy (information) propagation.
Ray tracing optical software is based on phase calculation. Using of negative refraction index for mirrors in software should not be confused with media negative index, meaning phase propagation in the opposite direction to the group speed.

Gleb,

 

Yes, that's correct of course. Some software (ATMOS, etc.) use the convention of negative refractive index values only to denote phase propagation in the opposite direction (reflection), not phase propagation higher than the speed of light (with no information propagation). Only refractive index values >1 carry information; the negative sign, if allowed, indicates only relative direction of wavefront propagation. 

 

Some software allow "negative" refractive index value of -1 only for reversal of phase propagation direction (reflection). Others prohibit negative refraction index values altogether, and  force you to enter or choose a verbal designation such as "reflector" so as to never even accidentally enter a negative refractive index.

 

IMO, delving into ref. index values <1 or even <0  has no practical application in amateur telescope making, not even as a mental exercise. 

 

Mladen

 

PS edit: typos


Edited by MKV, 14 June 2021 - 03:06 AM.

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#18 horizon

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Posted 14 June 2021 - 02:16 PM

There is a company wanting to commercialise meta lenses for consumer (smartphone camera) and automotive applications:

 

https://www.metalenz.com/

 

Most (all?) meta materials rely on structures that are smaller than or are on the order of the wavelength of the light passing through it. It's a matter of manufacturing these structures cheaply and consistently in order the move from the lab to consumer applications.

I your thinking about telescopes then think of a lens being manufactured like microchips on a silicon wafers.

 

Personally I'm very excited about this technology and hope to see more applications in the next decades.

 

Greetings,

 

Mike


Edited by horizon, 14 June 2021 - 02:19 PM.

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