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In the last year there has been fuzz regarding metamaterials studied for the purpose of cloaking, and it seem to me they are somewhat glorified 2D waveguides, but in any case it seems a reasonable application of this to funnel radiation captured over a wide area of incidence into smaller area, and i thought that this could be a cheap way to produce ignition radiation for a fusion reactor.

Reasons why this wouldn't work, or not produce enough energy density? All stuff i've read about fusion ignition with lasers doesn't seem to depend too heavily on the coherence of the radiation

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Assuming that you have a source whose temperature is T, the best any optics system can do (in applying the energy from the source to a target) is in such a way that the target may be heated up to the temperature T. This is because of a basic law of thermodynamics: heat flows from hot things to cold things and never vice versa.

There's another way of saying this that applies to imaging optics; that is, to optical systems that produce images. I'll edit it in if I find it. But the mechanism you're describing is more general than an optics system.

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Hmmmm. Can't seem to find it. It relates the product of the numerical aperture and the pupil size through a imaging system. Where you increase the pupil size you decrease the numerical aperture. Or at least that's what I recall. –  Carl Brannen Mar 20 '11 at 4:53
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If you read the laser fusion article in wikipedia you will see that white light is used in some designs to feed the lasers, not very efficiently. Better wave guides might improve efficiency but certainly cannot substitute for the energy concentration of lasers on the fuel pellets.

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