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Surface plasmon-polaritons (SPP) excited in periodic metallic gratings provide strong electromagnetic field localization at the interface. The applications of plasmonic structures are mainly sensors for magnetic and biochemical measurements. Besides such nanostructures are widely used in the laser technique applications, e.g. for lowering the threshold of the laser fluences sufficient for all-optical switching and optical demagnetization processes. The possibility to tune an SPP resonance (SPR) in real time is very attractive for fundamental and practical needs. It may be provided by active plasmonics studying the opportunities of SPR control using external stimulus.
Here we experimentally study the influence of nanostructure profile depth on the ultrafast SPR 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 magnetooptical response modulation. The latter is visualized using the pump-probe technique in the transverse magnetooptical Kerr effect (TMOKE) configuration. A 1-KHz Ti:Sapp regenerative amplifier is a pump source, and a super-continuum pulse is a probe. The modification of the SPP wave vector 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 SPR are affected by the surface corrugation depth of the plasmonic crystal. Their highest achieved values for the set of studied MPCs are of 10% and 0.7% respectively. The durations of laser-induced charge carriers thermalization and relaxation processes are also profile-dependent. Their typical values are of 400 fs for electron thermalization, of 1 ps for electron-phonon relaxation, and of several tens of ps for phonon-phonon relaxation process.
This research was supported by the Russian Foundation for Basic Research (Grants No. 17-52-560011, No. 18-52-45023) and MSU Quantum Technologies Center.
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