You've all seen an ordinary magnifying glass--it looks like a section of a glass sphere, maybe flat on one side, or maybe with both sides curved. Since all the bending of light happens at the surface, what happens if you cut out the excess and just use hundreds or thousands of little (disjoint) sections? Augustin-Jean Fresnel thought of it, and
developed the lenses that bear his name. His thought was for lighthouses to be more powerful by capturing and focussing more of the light, and it worked very well. There's graininess in the image you get when using these things, but that's the price you pay for compactness.
How do you focus X-rays? They can be scattered in coherent ways by crystals--suppose you used little slices of crystals tilted at increasing angles and stacked in rings?
Turns out somebody else thought of the idea first. The Laue lens uses crystals in concentric rings. You can get pretty decent focus, too: 8.4nm × 6.8nm .
2 comments:
Fresnels are very big in theater, or at least they were 40 years ago.
Undoubtedly they still are. You might be able to get similar effects with banks of LEDs, but even so I'd bet you could still harvest a little more useful light with the lenses.
Post a Comment