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Transient optical symmetry breaking for ultrafast broadband dichroism in plasmonic metasurfaces


Ultrafast nanophotonics is an emerging research field aimed at the development of nanodevices capable of light modulation with unprecedented speed1,2,3,4. A promising approach exploits the optical nonlinearity of nanostructured materials (either metallic or dielectric) to modulate their effective permittivity via interaction with intense ultrashort laser pulses. Although the ultrafast temporal dynamics of such nanostructures following photoexcitation has been studied in depth5, sub-picosecond transient spatial inhomogeneities taking place at the nanoscale have been overlooked so far. Here, we demonstrate that the inhomogeneous spacetime distribution of photogenerated hot carriers induces a transient symmetry breaking in a highly symmetric plasmonic metasurface. The process is fully reversible and results in a broadband transient dichroism with a recovery of the initial isotropic state in less than 1 ps, overcoming the speed bottleneck caused by slower (electron–phonon and phonon–phonon) relaxation processes. Our results pave the way to ultrafast dichroic devices for high-speed modulation of light polarization.

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Fig. 1: Ultrafast optical dichroism in a Au metasurface.
Fig. 2: Theoretical modelling.
Fig. 3: Broadband ultrafast dichroic transmittance.
Fig. 4: Symmetry-breaking window.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request. Source data are provided with this paper.


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We acknowledge financial support from Graphene FET Flagship Core Project 3 (grant no. 881603). G.D.V. and G.C. acknowledge support from the project METAFAST-899673-FETOPEN-H2020. G.D.V. and A.S. acknowledge support from the Italian MIUR under PRIN grant no. 2015WTW7J3. P.N. acknowledges support from the Robert A. Welch Foundation (grant no. C-1222).

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Authors and Affiliations



G.D.V. and G.C. conceived and designed the experiment. A.T., S.F. and R.P.Z. manufactured the samples and performed the static measurements. A.S., A.A., P.N. and G.D.V. developed the theory and designed the structures. A.S. performed the numerical simulations. M.M. performed the pump–probe experiment. G.C., R.P.Z. and P.L. supervised the experimental work. G.D.V., A.A. and A.S. wrote the first draft of the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Alessandro Alabastri or Giuseppe Della Valle.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–7, Discussion (eight sections I–VIII), Table 1 and refs. 1–41.

Source data

Source Data Fig. 1

Source data for Fig. 1b.

Source Data Fig. 2

Source data for Fig. 2e–h.

Source Data Fig. 4

Source data for all six panels of Fig. 4.

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Schirato, A., Maiuri, M., Toma, A. et al. Transient optical symmetry breaking for ultrafast broadband dichroism in plasmonic metasurfaces. Nat. Photonics 14, 723–727 (2020).

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