Research Themes

Time-interfaces

Time-interfaces are abrupt variations in electromagnetic properties of a material or metamaterial. Dual to the abrupt interface between e.g. the surface of water and air, these events can produce exotic effects such as time-reflection and broadband frequency conversion. Our group investigates fundamental electromagnetic properties for time-interfaces, as well as their applications for advanced wave control, such as frequency conversion, amplification and waveguiding effects.

Galiffi, E., Solís, D. M., Yin, S., Engheta, N., & Alù, A. (2025). Electrodynamics of photonic temporal interfaces. Light: Science & Applications, 14(1), 338.

Stefanini, L., Galiffi, E., Yin, S., Singh, S., Solís, D. M., Engheta, N., ... & Alù, A. (2025). Theory and Experimental Observation of Scattering by a Space-Time Corner. Physical Review Letters, 135(11), 113802.

Galiffi, E., Xu, G., Yin, S., Moussa, H., Ra’di, Y., & Alù, A. (2023). Broadband coherent wave control through photonic collisions at time interfaces. Nature Physics, 19(11), 1703-1708.

Moussa, H., Xu, G., Yin, S., Galiffi, E., Ra’di, Y., & Alù, A. (2023). Observation of temporal reflection and broadband frequency translation at photonic time interfaces. Nature Physics, 19(6), 863-868.

Yin, S., Galiffi, E., Xu, G., & Alù, A. (2023). Scattering at temporal interfaces: An overview from an antennas and propagation engineering perspective. IEEE Antennas and Propagation Magazine, 65(4), 21-28.

Galiffi, E., Yin, S., & Alú, A. (2022). Tapered photonic switching. Nanophotonics, 11(16), 3575-3581.

Floquet metamaterials

Time-interfaces are abrupt variations in electromagnetic properties of a material or metamaterial. Dual to the abrupt interface between e.g. the surface of water and air, these events can produce exotic effects such as time-reflection and broadband frequency conversion. Our group investigates fundamental electromagnetic properties for time-interfaces, as well as their applications for advanced wave control, such as frequency conversion, amplification and waveguiding effects.

Galiffi, E., Harwood, A. C., Vezzoli, S., Tirole, R., Alù, A., & Sapienza, R. (2025). Optical coherent perfect absorption and amplification in a time-varying medium. Nature Photonics (accepted). preprint: arXiv:2410.16426

Yin, S., Galiffi, E., & Alù, A. (2022). Floquet metamaterials. ELight, 2(1), 8.

Galiffi, E., Wang, Y. T., Lim, Z., Pendry, J. B., Alù, A., & Huidobro, P. A. (2020). Wood anomalies and surface-wave excitation with a time grating. Physical Review Letters, 125(12), 127403.

Tsai, Y. W., Wang, Y. T., Galiffi, E., Alù, A., & Yen, T. J. (2022). Surface-wave coupling in double Floquet sheets supporting phased temporal Wood anomalies. Nanophotonics, 11(15), 3509-3517.

Polaritons in low-symmetry materials

Polaritons are hybrid quasiparticled formed by the coherent exchange of energy between light and matter. In low-symmetry materials, these excitations can acquire exotic properties such as hyperbolic propagation, asymmetric loss profiles and axial dispersion. Some of our recent work on this topic involves the discovery and theory of shear polaritons in natural materials and in monoclinic metasurfaces, both electromagnetic and elastodynamic.

Galiffi, E., Carini, G., Ni, X., Álvarez-Pérez, G., Yves, S., Renzi, E. M., ... & Alù, A. (2024). Extreme light confinement and control in low-symmetry phonon-polaritonic crystals. Nature Reviews Materials, 9(1), 9-28.

Renzi, E. M., Galiffi, E., Ni, X., & Alù, A. (2024). Hyperbolic shear metasurfaces. Physical Review Letters, 132(26), 263803.

Yves*, S., Galiffi*, E., Ni, X., Renzi, E. M., & Alù, A. (2024). Twist-induced hyperbolic shear metasurfaces. Physical Review X, 14(2), 021031.

Matson, J., Wasserroth, S., Ni, X., Obst, M., Diaz-Granados, K., Carini, G., ... & Caldwell, J. D. (2023). Controlling the propagation asymmetry of hyperbolic shear polaritons in beta-gallium oxide. Nature communications, 14(1), 5240.

Time-diffraction and optical implementations of time-varying media

Polaritons are hybrid quasiparticled formed by the coherent exchange of energy between light and matter. In low-symmetry materials, these excitations can acquire exotic properties such as hyperbolic propagation, asymmetric loss profiles and axial dispersion. Some of our recent work on this topic involves the discovery and theory of shear polaritons in natural materials and in monoclinic metasurfaces, both electromagnetic and elastodynamic.

Tirole, R., Vezzoli, S., Galiffi, E., Robertson, I., Maurice, D., Tilmann, B., ... & Sapienza, R. (2023). Double-slit time diffraction at optical frequencies. Nature Physics, 19(7), 999-1002.

Tirole, R., Galiffi, E., Dranczewski, J., Attavar, T., Tilmann, B., Wang, Y. T., ... & Sapienza, R. (2022). Saturable time-varying mirror based on an epsilon-near-zero material. Physical Review Applied, 18(5), 054067.

Tirole, R., Vezzoli, S., Saxena, D., Yang, S., Raziman, T. V., Galiffi, E., ... & Sapienza, R. (2024). Second harmonic generation at a time-varying interface. Nature Communications, 15(1), 7752.