'Focussing' scattered light

[shapiro]

Is it possible to design a lens which would 'focus' scattered light. However, rather than producing a point across which all light would pass, the light would need to exit the lens(es) on parallel paths. I don't necessarily need a design (although if it exists that would be great) but rather just an indication as to whether the project is possible or indeed a pointer on how to begin.
Thanks in advance

 

[chicopee]

Well, I can focus the rays of the sun with a magnifying glass.
Isn't the reason for MASERS and LASERS to focus light beams that would otherwise scatter?

 

[shapiro]

Sorry I didn't really articulate the problem very well:
-Light enters the lens at any, unknown angle (as it does when it has passed through the atmosphere)
-Light leaves the lens with all rays parallel.
I'm sure you can now see why a magnifying glass would hardly suffice

 

[MadMango]

Probably something similar to some sort of Fresnel lens should work.

http://en.wikipedia.org/wiki/Fresnel_lens

"Art without engineering is dreaming; Engineering without art is calculating."


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[IRstuff]

Depends on what you mean by "scattered" and what you mean by "parallel."

If you mean perfectly scattered, i.e., over 2pi steradians and perfectly parallel, i.e., divergence of zero, then the answer is no.

If you mean "close enough," then you could use a fisheye lens, which takes any light entering over something close to 2pi steradians, and produces an image of the light field onto the relative small area of a sensor, then it's not too farfetched. However, the output would not be collimated, but would be mapped onto the active area of an imaging sensor.

Some caveats:
> a fisheye tends to have a very small entrance aperture, so its collection efficiency and cross-section is poor
> mapping is purely by angle of incidence onto the front aperture, where the angle corresponds to corresponding angular position within the fisheye lens' field of view (FOV).

TTFN

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[drawoh]

shapiro,

This is a better question for the Optical Systems forum.

A theoretical thin lens focuses collimated light all through one point. Any light present that is not collimated, will not go through the focus point.

Try to imagine a set of light rays converging on one point on the front surface of your lens. In your desired system, all of these beams pass through the surface all pointing in the same direction. You need a new law of physics to replace Snell's Law.

JHG

 

[1gibson]

Bundle of fiber optic cables that is spread into a "bouqet" at one end with individual collection lenses on each strand?

Seems pretty impractical but it popped into my head and seems to meet the basic requirements.

 

[drawoh]

1gibson,

My understanding is that light exits fibre optic at the same field of view it went in at. What is needed here is an intelligent lens. You will make millions if you can invent one.

JHG

 

[GregLocock]

I think 2LOT has a great deal to say about this.

Entropy of a collimated stream of photons~0

entropy of random light rays >= heaps.

Having said that the sun's rays are not quite as random as you might think.

One way to do it with less than 20% efficiency would be to use a solar cell to power a little laser.

Cheers

Greg Locock


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[Walterke]

If I remember my lessons in light/optics correctly, light from the sun is to be considered parallel, and not scattered. Thats why a magnifying glass does work.

If you mean actual scattered light, going in all directions, that would be more difficult, and maybe even impossible. GregLocock's light-powered-laser is probably your only shot then, but I don't think that's what you're looking for.

What exactly are you needing this for?

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Teamcenter 8

 

[jimkinney]

What about a Panoramic Annular Lens? Not quite scattered to prismatic, but closer.

Jim

Jim Kinney
Kennedy Space Center, FL

 

[IRstuff]

Here's something you can buy off the shelf:

http://www.superfisheye.com/SuperFisheye-Lens-Canon

WITH 185° field of view, resulting in images like:

http://www.superfisheye.com/Gallery/Dewarper-Demo#360pano

Note, however, distortion in this type of optic is extreme, and dewarping is usually nontrivial

TTFN

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[ornerynorsk]

I am curious as to the light source. Is it truly a scattered source, or originating from a single source? This may change the equation a bit.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[IRstuff]

No matter what optic you're using, you've alluded to single photon-type events, which means you need to have either:
> intensified camera
> electron-multiplication camera
> avalanche photodiode array camera

Whatever sensor it is, it'll need to be single-photon counting capable.

TTFN

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[lumenharold]

Without knowing what the OP wanted to do and the actual source it is kind of hard to solve his problem.

Just a thought though, I've have messed around with DLP systems and in the LED based products there is a pair of aspheric lenses immediate to the LED. They are there to collimate the Lambertian source. Adding a third element in front off a pair of aspheric lenses to capture and then focus light to a bundle approximating the emitter surface on an LED wouldn't be the single element solution the OP was looking for but should work. Might be a little lossy depending on coatings, etc. Might be able to use a parabolic reflector for the first element to capture as much light as possible.

Harold
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