Lensless focusing with subwavelength resolution
Wed Aug 16 09:26:26 BST 2006
[Applied Physics 88 261107] discusses production of a focused spot below the Rayleigh limit by coherently combining several beams together to match the field emitted by a point source.
I remember seeing a seminar about this technique a couple of years ago, I think the lecturer was from a group in the Netherlands though (this group is from MIT). The seminar I remember used a quadrant waveplate to produce the desired optical field, this group uses 15 mirrors to produce the field. In principle this could be used with diffractive optics to allow focusing of X-rays etc, where the refractive index of traditional optical materials is not sufficiently different from vacuum to allow tradiotional optical elements.
Moral of the story: phase coherence lets you do fun things! It is worth the extra experimental design complexity to at least consider making things phase coherent on some timescale.
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