ИСТИНА

The study of optical effects in hybrid nanoscale metasurfaces represents a significant field of nanophotonics. Hybrid metal-dielectric metasurfaces combine the unique properties of metals and dielectrics, and various resonances can be exited at a metal-dielectric interface. For example, periodic array of nanoparticles can support surface lattice resonances (SLR). Another rapidly developing field is ultrafast all-optical control. “Pump-probe” femtosecond spectroscopy technique can achieve sufficient temporal resolution to detect nonequilibrium electron gas heating [1]. Moreover, there are number of studies that describes electron gas relaxation processes. The intersection of these two scientific areas is ultrafast plasmonics [2], which unites nanoscale structures with subpicosecond processes. In this work the gold dielectric permittivity time dependencies based on evolution of the electron energy distribution following a femtosecond laser pulse were calculated on the basis of the two-temperature model [3] the Boltzmann kinetic equation and interband theory. The maximum change in the electron gas temperature is 1500 K and the final change in the lattice temperature is 60 K, which is in agreement with theoretical estimates. The calculations were used to describe anomalous temporal behavior of the 2D periodic array of gold nanospheres coated with a layer of bismuth-substituted iron-yttrium garnet, which was experimentally studied earlier [4]. [1] F. Caruso and D. Novko Adv. Phys. X, vol 7, 2095925, (2022) [2] Stoll T. et al., Eur. Phys. J. B, vol. 87, 1-19, (2014). [3] Anisimov S. I. et al., Sov. Phys. JETP, vol. 66, 375-377, (1974). [4] Kiryanov M. A. et als., JETP Lett., vol. 117, 196-201, (2023).