Lukáš Halagačka

Coupled mode enhanced giant magnetoplasmonics transverse Kerr effect

We show that the enhancement of the transverse magneto-optical Kerr effect of a smooth magnetic dielectric film covered by a noble metal grating, is strongly dependent on the precise geometry of this grating. Up till now this magnetoplasmonic enhancement was solely attributed to a nonreciprocal shift of the dispersion of the surface plasmon polariton resonances at the interface with the magnetized substrate. It is demonstrated that by hybridization of surface and cavity resonances in this 1D plasmonic grating, the transverse Kerr effect can be further enhanced, extinguished or even switched in sign and that without inverting or modifying the films magnetization. This strong geometrical dispersion and the accompanying anomalous sign change of the magneto-plasmonic effects in such systems has never been considered before, and might find interesting applications in sensing and nanophotonics.

Mueller matrix optical and magneto-optical characterization of Bi-substituted gadolinium iron garnet for application in magnetoplasmonic structures

A ferromagnetic garnet, used as a magneto-optical (MO) material in magneto-photonic and magneto-plasmonic structures, is characterized. We present a general procedure to determine optical and magneto-optical functions of the magneto-optic garnet by using Mueller matrix ellipsometry. In the first step, the optical functions (the refractive index spectra) of the (CaMgZr)-doped gallium-gadolinium garnet (sGGG) substrate and the Bi-substituted gadolinium iron garnet Gd1.24Pr0.48Bi1.01Lu0.27Fe4.38Al0.6O12 (Bi:GIG) are obtained in the spectral range from 0.73 eV to 6.42 eV (wavelength range 193 nm – 1.7 μm). Subsequently, the spectra of the magneto-optical tensor components are obtained by applying an external in-plane magnetic field in longitudinal and transverse geometry. The obtained functions are then used to fit the Mueller matrix spectra of a magneto-plasmonic structure with a gold grating on the magneto-optic garnet layer. This structure has recently been demonstrated to have strongly enhanced transverse magneto-optic Kerr response at visible and near-infrared frequencies. By taking possible fabrication imperfections (surface roughness, residual photo-resist layer, thickness deviation) into account, the measured strongly enhanced MO response fits very well to the numerical model predicting these exaltations.

Magneto-optical properties of InSb for terahertz applications

Magneto-optical permittivity tensor spectra of undoped InSb, n-doped and p-doped InSb crystals were determined using the terahertz time-domain spectroscopy (THz-TDS) and the Fourier transform far-infrared spectroscopy (far-FTIR). A Huge polar magneto-optical (MO) Kerr-effect (up to 20 degrees in rotation) and a simultaneous plasmonic behavior observed at low magnetic field (0.4 T) and room temperature are promising for terahertz nonreciprocal applications. We demonstrate the possibility of adjusting the the spectral rage with huge MO by increase in n-doping of InSb. Spectral response is modeled using generalized magneto-optical Drude-Lorentz theory, giving us precise values of free carrier mobility, density and effective mass consistent with electric Hall effect measurement.

Experimental demonstration of anomalous nonreciprocal optical response of 1D periodic magnetoplasmonic nanostructures.

In this paper we analyze the optical and transversal magnetooptical (MO) response of magnetoplasmonic (MP) nanostructures. The MP structure is a 1D periodic gold grating fabricated by lift-off technique on the MO dielectric substrate (Bi-substituted yttrium iron garnet BixY3−xFe5O12). Following our recent theoretical work (Opt. Express 21, pp. 2174121755, Sep 2013.), we confirm here experimentally the predicted dependence of the MO response on the geometry of the grating, that is directly attributed to the anticrossing behavior of the Fabry-Perot (FP) resonance in the grating’s slits and the surface plasmon resonances (SPPs) at its interfaces. The experimental results were achieved by Mueller matrix spectroscopic ellipsometry. Observed fine tuning of the transverse magneto-optic Kerr opens up new possibilities for the design of compact nonreciprocal devices.

Optical spectroscopy of terbium-scandium-aluminium garnet and terbium-scandium perovskite

Tb3Sc2Al3O12-TbScO3 eutectic crystallizes in a rodlike microstructure, and its potential to exhibit photonic bandgap has been presented tentatively. In order to model its optical properties there is a need for precise determination of the optical properties of its component materials in a wide spectral range. Spectroscopic data in the range from 0.6 to 6.5 eV (190-2100 nm) were obtained using spectroscopic ellipsometer UVISEL, Horiba Jobin-Yvon. The measurement was completed with mid infrared reflection data using Bruker FTIR spectrometer in the spectral range from 7500 to 550 cm-1. Optical functions were obtained using fitting of the data with model dielectric function fulfilling the Kramers-Kronig dispersion relations. Obtained optical functions enable to model the optical properties of self-organized eutectic micro- and nanostructures.

Surface plasmon resonance system with magneto-optic garnet

We demonstrate the model specification of the MO-SPR coupling-prism system consisting of the Ag film deposited between two garnet layers; the water is supposed as an analyte. The bismuth-doped gallium-gadolinium iron garnet offers low optical losses as well as strong MO response from visible to near infrared optical region. We apply two different response functions that detect a change of analyte refractive index that operate either directly with reflectance change at appropriate incidence angle or with the magneto-optically highlighted SP resonance dip shift. Suggested sensitivity criteria lead to the sensitivity about 120 1/RIU or 75 deg/RIU with the resolution of the order 10-5 RIU by experimentally acceptable variation of response factors.

Spectroscopy of materials for terahertz photonics

In this paper we apply the terahertz time-domain spectroscopy (THz-TDS) to obtain optical function spectra in the range from 0.06 to 3 THz. Polarization sensitivity is obtained using azimuth-controlled wire-grid polarizers. We demonstrate general methods on characterization of plasmonic semiconductors. Detail characterization of optical and magneto-optical material properties is also motivated by a need of optical isolator in THz spectral range. The technique is applied to III-V semiconductors. The typical material is a single crystal undoped InSb having the plasma frequency in the range of interest. With appropriate magnetic field (in our case 0.4 T) we observed coupling of plasma and cyclotron behavior of free electrons with gigantic magneto-optic effect in the THz spectral range.

Magnetoplasmonic waveguiding structure with nonreciprocal dispersion of guided TM modes

In this paper we present our study of waveguiding structure with nonreciprocal dispersion of guided modes. The considered structure is based on the Silicon waveguide core and the plasmonic (gold) 1D periodic grating. The waveguide and the grating are separated by low refractive index layer (SiO2). The structure operates as follows. The evanescent field of the guided mode is used for the excitation of the surface plasmon polaritons (SPPs) at the top side of the grating. To achieve non-reciprocity the magneto-optical dielectric garnet is assumed to be on the top of the grating. The presence of the transversal magnetization in the garnet leads to the nonreciprocal shift of the SPP. Together with the evanescent coupling of guided modes this leads to the nonreciprocal dispersion of guided mode. The grating period is varied to achieve coupling of grating’s resonances with the waveguide evanescent field and therefore possible enhancement of the nonreciprocal response.

Modeling of anisotropic grating structures with active dipole layers

In our previous paper [T. Fördös, et al., J. Opt. 16 (2014) 065008] we have proposed a new approach for modeling of polarized light emission from anisotropic multilayers with active dipole layers. The method is suitable to model spin-polarized light emitting diodes (spin-LED) and spin-lasers. This paper deals with generalization of the approach to scattering matrix (S-matrix) formalism and to laterally periodic structures in the frame of rigorous coupled wave algorithm (RCWA). We use expansion of the permittivity tensor in a grating layer into Fourier series and the periodic electromagnetic field in the structure is expressed using a matrix method including appropriate boundary conditions. The new approach based on S-matrix formalism is also suitable for modeling of monomode emission from MQW laser structures with multiple source layers.

Magneto-optics: from bulk materials to nanostructures

In this paper, we review two main recently dominating applications of magneto-optics (MO). The first one is related to a unique MO non-reciprocity. For example, the MO non-reciprocity in the isolators enables complete transmission in the forward propagation direction, while it prevents spurious back-reflection, which is needed to preserve proper operation of active optical elements like lasers or amplifiers in optical systems. Local enhancement of MO activity by optical field concentration in nanostructured magneto-plasmonic and magneto-photonic systems opens new horizons in optical isolators, circulators, and switches. We will discuss enhancement of MO effects using surface magneto-plasmons in periodic grating and apply it to nonreciprocal isolating systems. The second main application of the magneto-optics is the characterization of magnetic multilayers, periodic systems, and nanostructures. MO techniques profit from high near-surface sensitivity to local magnetization, nondestructive character, ultrafast response, and possibility to measure all components of the magnetization vector by means of MO vector magnetometry. Furthermore, the MO Kerr effect allows the separation of magnetic contributions originating in different depths, different materials in multilayer systems as well as laterally modulated and self-organized nanostructures fabricated via modern nanotechnologies.