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.
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