Jaroslav Vlček

Numerical study on the spectroscopic ellipsometry of lamellar gratings made of lossless dielectric materials

The spectroscopic ellipsometry of lamellar gratings made of lossless dielectric materials is studied numerically by using the rigorous coupled-wave method with the use of Lis Fourier factorization rules [J. Opt. Soc. Am. A 13, 1870 (1996)], which are known to improve the convergence on the analyses of metallic gratings. Numerical results show that the calculation method also provides fast convergence on lossless gratings, and accurate values of the ellipsometric angles are obtained in very short computation times. Moreover, estimation of grating parameters is investigated by using a cost function defined by the average distance on the Poincaré sphere, and it is shown that the computation required for accurate estimation is possible in reasonable computation time.

Total internal reflection ellipsometry of periodic structures

The theoretical model of the evanescent waves coupling with dielectric and metallic strip gratings is described. The interaction of electromagnetic field with lamellar periodic structures and their diffraction properties are determined by coupled wave method implemented as the Fourier modal method. The simulations of the ellipsometric response under internal reflection for different geometrical and material configurations are presented. The attention is concentrated on the study of coupling strength influence, effects connected with stripes geometry, and, with absorption in metallic elements of grating.

Spectral ellipsometry of binary optic gratings

The coupled wave method (CWM) has been applied to the description of electromagnetic wave propagation in binary optic gratings. The electromagnetic field and the permittivity profile are expanded into two-fold Fourier series. The reflection coefficients of 2D periodical structures have been specified and the ellipsometric angles of discussed shapes have been computed. The theoretical results computed for SiO2 and Si3N4 dots are compared with experimental data obtained for the square silicon nitride dots on the Si substrate. The measurements were performed using computer controlled four zone null ellipsometer in spectral range from 240 nm to 700 nm. The influences of Si02 ultrathin oxidation layer and dot thickness on spectral ellipsometric angles are also discussed.

Magnetic defectoscope with permanent magnets

The paper is intended for the theory of magnetic defectoscope of steel ropes, construction of this equipment and evaluation of measured data. The detector module consists of magnetization head, sensing system and holder with optoelectronic rotary increment encoder. The wavelet transform — a new and promising method for defectoscope signal processing — is presented. It enables to specify the changes of the rope cross-section with an accuracy level better than 0.5%.

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.

Designing of MO-SPR bio-chip with photonic crystal

The magneto-plasmonic response in planar multilayer with prism coupling composed from Fe and Au bilayer supplied by photonic crystal (Ta2O5 / SiO2) is studied. Modeled structure is intended as a sensor unit combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The sensitivity of MO-SPR system by small variations of analyte refractive index is tested to obtain optimal resolution ability.

Magneto-plasmonic response as a perspective tool to magnetic field sensing

The non-reciprocity of magneto-optical reflection response by surface plasmon excitation in the planar Au/Fe/Au/glass nano-systems with prism coupling is studied. These structures are intended as magnetic field sensor units combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The ability of MO-SPR systems to magnetic field sensing is analysed using incidence-angle-depending response function (Rpp (+) – Rpp (-))/(Rpp (+) + Rpp (-)), where Rpp denotes the reflectance of p-polarized beam; and, the sign in upper index relates to the orientation of external magnetic field. The proposed sensitivity criteria F and K (the magnitude and inflexed tangent of the response function oscillation) are applied in transverse MO configuration. Mathematical model based on the own matrix algorithm is applied to simulate the diffraction response to varying external magnetic field at the wavelength 632.8 nm. Obtained theoretical results are compared with experiments realized using the measuring device Multiskop (Optrel GbR, Germany).

Effective medium approximation of anisotropic materials with radiative correction

A measurable magneto-optical activity of nanoparticles made out of noble metals is observed when the localized plasmon waves are excited in the presence of external magnetic field. We confirmed these observations for quite general Au nanostructure on SiO2/Si substrate theoretically and by experimental way. The heterogeneous layer is formed as a field of cylindrical or spheroidal nanodots of various size having the same height and parallel symmetry axis. These properties enable to apply the Bruggeman’s model of effective medium approximation, for which the size of dots (height, diameter) and fill-factor of nanodots were specified using the transmission electron microscopy image processing. Actually, this model is extended about the interaction of magnetic dipole moments simulated using discrete dipole approximation via geometrical averaging. Derived computational algorithm leads to better agreement with experimental data in the form of Kerr angles in polar configuration at visible spectral region. Obtained out-puts also illustrate the fact that extinction peak of plasmon excitation is located at the resonance wavelength of permittivity.

Surface plasmon structures with ferromagnetic thin films

The paper is devoted to Au/Fe/Au/glass and Au/Fe/glass structures intended as MO SPR sensor units. The model approach based on matrix algebra is used to describe the response of discussed structures to external magnetic field. The theoretical results are confirmed by experiments realized by Multiscope device. The attention has been focused on a sensitivity of proposed response factors ρ±(Φ) and F to magneto-optical effects. The application of ρ±(Φ) response factor for our structures description is limited. The F factor has practically linear character such as change of external magnetic field and ferromagnetic thin film thickness.

Magneto-optical phenomena in systems with prism coupling

The prism coupler allows the resonant excitation of leaky modes whose transverse field distribution in the guiding structure is close to that of guided waves. The paper is concentrated on the study of the influence of the associated electromagnetic resonances on the linear response of this distributed coupler while taking into account the width of coupling gap and the induced anisotropy of waveguiding media. The characteristics of prism coupling into anisotropic thin films are calculated by 4×4 matrix algebra.