A monochromatic beam of light may be resolved as the sum of two linearly polarised beams in perpendicular planes, their phases displaced by some constant angle p . The device must reverse this displacement, delaying (say) one linear component by angle 2 p . Now consider an individual photon in such an input beam. The corresponding output phase must somehow be smeared between values at separation 2 p , in general impossibly. So sticking my neck out, I conclude that *** Salamin's demon (or genie?) is nonexistent. *** Caveat: my regrettable ignorance concerning elementary physics in general and optics in particular has been only barely perceptibly ameliorated by wrestling with this engaging problem. But even if I have (once again) blown it above, at least I now understand circular polarisation: an ultimately simple business which previously appeared ineffably mysterious. Fred Lunnon On 6/1/15, Eugene Salamin via math-fun <math-fun@mailman.xmission.com> wrote:
Here is a puzzle concerning the optics of polarized light. Every state of polarization has its opposite. For linear polarization, it's linear but rotated 90 degrees. For circular polarization, it's circular with opposite helicity. For general elliptic polarization, it's elliptic with the ellipse rotated 90 degrees, and the helicity reversed. On the Poincaré sphere, opposite states of polarization are represented by diametrically opposite points. The puzzle is to construct an optical device that reverses the polarization state. For any input, the output is the opposite polarization. Or, prove that it can't be done. -- Gene
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