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.
KEYWORDS: Near field optics, Near field scanning optical microscopy, Nanostructures, Visual optics, Visualization, Dielectrics, Light, Optical resonators, Photonics, Control systems
Subwavelength optical resonators and scatterers are dramatically expanding the toolset of the optical sciences and photonics engineering. By offering the opportunity to control and shape light waves in nanoscale volumes, recent developments using high-refractive-index dielectric scatterers gave rise to efficient flat-optical components such as lenses, polarizers, phase plates, color routers, and nonlinear elements with a subwavelength thickness. Here, we take a deeper look into the unique interaction of light with amorphous silicon scatterers by tapping into their resonant modes with a localized subwavelength light source—an aperture scanning near-field probe [1,2]. Scanning near-field optical microscopy (SNOM) is a powerful tool to image the near-field distribution of resonant optical modes supported by nanophotonic structures with sub-diffraction resolution. Our experimental configuration essentially constitutes a dielectric antenna that is locally driven by the aperture probe [3].
In stark contrast to the mostly uneventful far-field extinction response, a rich variety of distinct patterns of bright spots—corresponding to enhanced transmittance of the probe excitation—is observed in the near-field scans. Various transverse magnetic (TM) and transverse electric (TE) Fabry-Perot-like modes of different mode parities in a variety of nanostructure geometries can be revealed using full field 3D finite difference time domain simulations and group theory.
[1] A. Frolov et al. Nano Letters 2017, 17 (12), 7629–7637
[2] A. Frolov et al. in preparation 2018
[3] D. Denkova et al., ACS Nano 2013, 7, 3168–3176
We have demonstrated remarkable enhancement of longitudinal and transverse magneto-optical Kerr effects in magnetoplasmonic crystals based on thin nanostructured films of nickel and iron due to resonant excitation of magnetoplasmonic waves in Faraday and Voight configurations . Manifestations of ultrafast time-dependent transverse magneto-optical Kerr effect are experimentally demonstrated in femtosecond laser pulses reflected from a one-dimensional magnetoplasmonic crystal. We show that exciting surface plasmon-polaritons with magnetization-dependent dispersion law allows one to control the shape of the refected pulse.
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