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Observation of toroidal pulses of light

Abstract

Transverse electromagnetic waves are important carriers of information and energy. In 1996, Hellwarth and Nouchi theoretically identified a radically different, non-transverse type of electromagnetic pulse with a toroidal topology. These pulses, which are propagating counterparts of localized toroidal dipole excitations in matter, exhibit unique electromagnetic wave properties and, so far, have never been experimentally realized and observed. Here we report the generation of such toroidal light pulses in the optical and terahertz regions by the use of tailored nanostructured meta-surfaces. This achievement paves the way for experimental studies of energy and information transfer with toroidal light pulses, their space–time coupling and their light–matter interactions involving anapoles, localized space–time coupled excitations, skyrmions and toroidal qubits, which are of growing interest for the fundamental science of light and applications.

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Fig. 1: Characteristics of TLPs and blueprint for their generation.
Fig. 2: The spatio-spectral and spatiotemporal structure of generated optical TLPs.
Fig. 3: The spatiotemporal and spatio-spectral structure of generated terahertz TLPs.

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Data availability

The data from this paper can be obtained from the University of Southampton ePrints research repository at https://doi.org/10.5258/SOTON/D2261.

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Acknowledgements

We are grateful to S. Pidishety for experimental assistance. This work was supported by the UK Engineering and Physical Sciences Research Council (grant no. EP/ M009122/1), MOE Singapore (grant no. MOE2016-T3- 1-006), the European Research Council (Advanced grant FLEET-786851, funder ID https://doi.org/10.13039/501100000781) and the Defense Advanced Research Projects Agency (DARPA) under the Nascent Light Matter Interactions programme. T.E. acknowledges funding for this research from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 715362). G.L. and T.E. acknowledge support from an NSFC-ISF joint grant (grant no. 12161141010; 3450/21). G.L. is financially supported by the National Natural Science Foundation of China (91950114 and 11774145), Guangdong Provincial Innovation and Entrepreneurship Project (2017ZT07C071) and the Natural Science Foundation of Shenzhen Innovation Commission (grant no. JCYJ20200109140808088).

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Authors

Contributions

A.Z. performed the optical experiments with support from N.P. and N.I.Z. Y.S. performed experiments to verify the absence of OAM in TLPs. C.M. performed the terahertz experiments with support from T.E. J.D. fabricated the terahertz meta-surface. T.E. and G.L. supervised the terahertz part. All authors contributed to the analysis and interpretation of the results. N.P. and N.I.Z. wrote the manuscript with input from all authors. N.I.Z. supervised the work.

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Correspondence to Nikitas Papasimakis.

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Nature Photonics thanks Shuang Zhang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–16 and Sections 1–12.

Supplementary Video 1

3D view of transverse electric field of the generated TLPs as retrieved by interferometric experiments. Red and blue colours represent regions of electric field with opposite phases.

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Zdagkas, A., McDonnell, C., Deng, J. et al. Observation of toroidal pulses of light. Nat. Photon. 16, 523–528 (2022). https://doi.org/10.1038/s41566-022-01028-5

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