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Old Jan 28th 2014, 05:34 PM   #1
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Smile Coherent solar concentrator

Attached is a diagram for an idea to produce a coherent beam (somewhat similar to a laser) from sunlight. A paraboloid takes parallel rays and reflects them so that they concentrate and pass though a single point. It can also do the opposite, taking a set of rays from a single point and reflecting them so they are parallel. This would suggest that two parabolas with a common foci could serve to concentrate a parallel beam. A large parabola could gather a relatively large amount of rays and deliver them to a smaller parabola to be straightened. The attached picture is a visual representation of such a scheme. Sunlight is relatively parallel, so in theory such an apparatus could be used to produce a very strong coherent beam of reflected sunlight. So the question is: Is sunlight parallel enough? Would small deviations from perfect parabolas destroy the effect? What would be the effective range? Chromic aberration shouldn't happen because mirrors are used instead of lenses, but is there any other issues to watch out for? Thanks
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Coherent solar concentrator-diagram.png  
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Old Jan 29th 2014, 04:43 AM   #2
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This will not produce coherent light (i.e. light of a single wave length where the waves are in sync), as it doesn't filter out unwanted wavelengths nor does it have a mechanism to make the waves coherent. What you've have actually drawn is a design of a reflecting telescope known as a Gregorian, invented back in 1663. See: http://en.wikipedia.org/wiki/Reflecting_telescope
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Old Jan 29th 2014, 10:10 AM   #3
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Alright, thank you for that insight. It doesn't seem that it is exactly the same, however. A Gregorian telescope uses a parabola to collect the light and a ellipsoid to focus it to a point (http://en.wikipedia.org/wiki/Gregorian_telescope). That does seem to indicate that the basic principle could work though. I apologize for misusing the term of coherence. I meant that the rays would be parallel creating a beam, not that they would be in sync. My primary purpose for this proposal is to determine whether it could be useful for industrial processes in space. If something could be constructed from mirrors that would act similar to a high power cutting laser, that would have uses for vapor casting, cutting and industrial heating. However, it might be more practical to use solar cells and a electric laser (or direct electric heating) if it requires the collecting parabola to be nearly perfect or the range is incredibly short. Thanks
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Old Feb 1st 2014, 04:35 AM   #4
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Concentrating the beams could give great intensity, but it wouldn't be similar to a laser in which coherence is a necessary condition. In a laser, all the emissions are in phase, there is no phase difference. Coherence can be present even if there is a phase difference. However, this phase difference should not vary with time. The original emitters on the sun won't be coherent sources.
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