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Linked and knotted beams of light

An Erratum to this article was published on 01 October 2008

Abstract

Maxwell’s equations allow for curious solutions characterized by the property that all electric and magnetic field lines are closed loops with any two electric (or magnetic) field lines linked. These little-known solutions, constructed by Rañada1, are based on the Hopf fibration. Here we analyse their physical properties to investigate how they can be experimentally realized. We study their time evolution and uncover, through a decomposition into a spectrum of spherical harmonics, a remarkably simple representation. Using this representation, first, a connection is established to the Chandrasekhar–Kendall curl eigenstates2, which are of broad importance in plasma physics and fluid dynamics. Second, we show how a new class of knotted beams of light can be derived, and third, we show that approximate knots of light may be generated using tightly focused circularly polarized laser beams. We predict theoretical extensions and potential applications, in fields ranging from fluid dynamics, topological optical solitons and particle trapping to cold atomic gases and plasma confinement.

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Figure 1: Construction of the Hopf fibration.
Figure 2: Time evolution of the field lines and energy density of the Hopf knot.
Figure 3: Field-line structure of single-frequency CK curl eigenstates.
Figure 4: A generalization of the Hopf fields on the basis of the VSPHs, obtained using l=2,m=2 multipole fields and the spectrum of equation (5).

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Acknowledgements

We gratefully acknowledge discussions with M. Srednicki, J. Hartle and K. Millett. We thank V. Vitelli, C. Simon and F. Azhar for comments on the manuscript. W.T.M.I. gratefully acknowledges support from the English Speaking Union through a Lindemann Fellowship. D.B. acknowledges support from Marie Curie EXT-CT-2006-042580.

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Correspondence to William T. M. Irvine.

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Irvine, W., Bouwmeester, D. Linked and knotted beams of light. Nature Phys 4, 716–720 (2008). https://doi.org/10.1038/nphys1056

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