ИСТИНА

The concept of active plasmonics is tailoring the surface plasmon (SP) resonances using an external stimulus like magnetic field application, mechanical stress, laser irradiation, etc. The latter is attractive because the pulse duration of conventional ultrashort lasers is comparable with the plasmonic lifetime. Pumping the plasmonic crystal by an ultrafast laser pulse looks prospective for some practical applications like all-optical switching and heat-assisted magnetic recording. The approach of tuning the SP resonance by the laser radiation induces another fundamental issue of the SP influence on the laser-induced carriers dynamics. This question was thoroughly studied for the plasmonic structures based on the materials with low absorption. The materials support the laser-induced carriers density change as the primary mechanism of dynamics. However, the problem of the ultrafast laser-induced carrier dynamics in the ferromagnetic-based magnetoplasmonic structures remains up to date. In this work, we experimentally demonstrate the ultrafast laser-induced carriers dynamics in 1D nickel-based magnetoplasmonic crystals with different corrugation depth. The durations of laser-induced charge carriers' thermalization and relaxation processes are shown to be profile-dependent. To explain the difference, we introduce the mechanism of surface shape limitations of electron heat transfer. The values and times of the ultrafast magneto-optical modulation are derived. The question of the laser-induced modification of SP enhanced magneto-optical response is discussed. The samples are 1D profile-tailored nickel-based magnetoplasmonic crystals. The variation of corrugation depth changes conditions for the SP excitation as well as optical and magneto-optical spectra in a steady state. This fact allows us to expect different laser-induced charge carriers dynamics and, consequently, different ultrafast SP resonance control capabilities. It is shown that moderate fluence of 6 mJ/cm2 can induce ultrafast charge carriers' dynamics in all considered nanostructures resulting in their optical and magneto-optical response modulation. The latter is visualized using the pump-probe technique in the transverse magneto-optical Kerr effect (TMOKE) configuration. A 1-KHz Ti:Sapp regenerative amplifier is a pump source, and a super-continuum pulse is a probe. The differential reflectance and magneto-optical contrast are used for the quantitative characterization of the laser-induced modulation. Both optical and magneto-optical modulation are mostly observed in the spectral vicinity of the SP resonance on the timescale of 100 fs pump pulses. The modification of the SP wave vector, as well as the ultrafast demagnetization process under the pump pulse irraditation, may be considered as the physical reason of modulation in both non-magnetic and magnetic cases. The peak reflectance and TMOKE spectra modulation values in the spectral area of SP resonance are affected by the surface corrugation depth of the plasmonic crystal. Their highest achieved values for the set of studied magneto-plasmonic crystals are of 10% and 40%, respectively. The durations of laser-induced charge carriers' thermalization and relaxation processes are also profile-dependent. This research was supported by the Russian Foundation for Basic Research (Grants No. 20-02-00758, 17-52-560011) and MSU Quantum Technologies Center.