National Repository of Grey Literature 25 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Rigorous electromagnetic theory of the optical response of periodic nanostructures
Navrátil, Josef ; Antoš, Roman (advisor) ; Richter, Ivan (referee)
The diffraction of light is an important phenomenon with wide physical and engineering appli- cations and diffraction gratings are optical components with a periodic structure which are used to diffract light into several beams propagating in various directions. Direct methods like AFM or SEM proved to be insufficient to study the shape of planar diffraction gratings and therefore they must be supplemented with results obtained from optical spectroscopy. Computer simulations are the integral part of this method. This Thesis is focused on two particular simulation methods - the RCWA and the C-Method. It gives a rich theoretical introduction, discusses the weaknesses of these methods and also describes improvements of the RCWA using the Airy-like series and proper Fourier factorization. Both methods are implemented, tested on simple examples and af- terwards the convergence for particular cases is investigated. The C-Method and the modified RCWA algorithm exhibit excellent convergence. At the end, the numeric results are compared with experiments, giving a very good agreement in the ellipsometric parameters. 1
Studium elektrického pole v detektorech záření pomocí Pockelsova jevu
Hakl, Michael ; Franc, Jan (advisor) ; Richter, Ivan (referee)
Study of electric field in radiation detectors by Pockels effect (Master Thesis) by Michael Hakl Abstract Cadmium Telluride (CdTe) is a convenient candidate for room tem- perature detection of X-ray and gama radiation due to 1.5 eV band- gap energy and high atomic mass. Since CdTe has the highest linear electro-optical coefficient among II-VI compounds, the detector rep- resents a Pockels cell. Transmittance of the crystal is modulated by the internal electric field. Processing of infrared camera photographs results in an electric field profile between biasing electrodes. The elec- tric field in semi-insulting CdTe is influenced with deep level traps causing charge polarization under the electrodes. Occupation of traps is dependent on metal-semiconductor interface. Relation of charge accumulation and band bending for gold and indium contacts was studied. Repolarization/depolarization induced by additional illumi- nation with sub/above bandgap excitation laser was observed and ex- ploited for determination of the deep level energy. Results obtained by the Pockels-effect method were supported with luminescence measure- ments. Correlation between the occurrence of deep levels and surface point defects was discovered. Keywords: Pockels electro-optical effect, Cadmium Telluride ra- diation detector, Electric field, Schottky...
Charge transport in semiconductor nanostructures investigated by time-resolved multi-terahertz spectroscopy
Kuchařík, Jiří ; Němec, Hynek (advisor) ; Pereira, Mauro Fernandes (referee) ; Richter, Ivan (referee)
Terahertz conductivity spectra contain information on charge transport mechanisms and charge confinement on nanometer distances. In this thesis, we make a substantial progress in understanding of terahertz conductivity in several regimes. First, we theoretically investigate linear terahertz conductivity of confined electron gas: while the spectra of degenerate electron gas exhibit geometrical resonances, the response in non-degenerate case smears into a single broad resonance due to the wide distribution of charge velocities. Then, we theoretically and experimentally analyze various TiO2 nanotube layers: their linear charge transport properties strongly depend on the fabrication process, which influences the internal structure of the nanotube walls. In the main part of the thesis, we develop a framework for evaluation of the nonlinear terahertz response of semiconductor nanostructures based on microscopic Monte-Carlo calculations. The nonlinear regime is highly non-perturbative even in moderate fields as illustrated by efficient high harmonics generation. We investigate measurable nonlinear signals for various semiconductor nanostructures; metallic nanoslits filled with nanoelements are the most promising for the experimental observation of terahertz nonlinearities. These nonlinearities per unit charge are...
Vedené vlny v periodických strukturách a jejich senzorové aplikace
Vala, Milan ; Homola, Jiří (advisor) ; Richter, Ivan (referee)
This work is introduced by the description of fundamental properties of surface plasmons, propagating along the metal-dielectric interface and along the structure with thin metal film surrounded by the dielectrics with identical refractive indices. It is shown, that the excitation of two coupled modes (long-range surface plasmon - LRSP and short-range surface plasmon - SRSP) on symmetrical structure with a thin metal film is possible. Further, a brief overview of surface plasmons applications in optical sensors is presented. The diffractive multi-layer structure supporting LRSP and SRSP modes, which consists of the thin gold film surrounded by the dielectrics with slightly different refractive indices is designed. The diffractive structure is optimized using rigorous integral method for an application in SPR sensor. Diffractive structures with optimal parameters are prepared and characterized optically and using atomic force microscopy. In the end, an application of developed diffractive structure in SPR sensor with wavelength modulation is demonstrated.
Application of the FDTD technique to modelling of imaging in biophotonics
Říha, René ; Richter, Ivan (referee) ; Petráček, Jiří (advisor)
This thesis deals with the problem of practical application of FDTD technique for simulation of image formation in coherence controlled holographic microscope. Various ways for obtaining scattering matrices are explored in detail and the optimal technique based on a rigorous calculation of the far field is proposed. The scattering matrix, containing information about the observed sample, is subsequently used in analytic calculation of holographic signal; two levels of approximation of pupil function are also evaluated. The results are compared with a traditional approach based on Rytov approximation resulting in specification of the parameter domain where the approximation is applicable. Based on the simulations of the microscope, the dependence of axial resolution on apertures of the objective and the condenser and sensitivity of the signal to changes of refractive index of the sample is also studied.
Charge transport in semiconductor nanostructures investigated by time-resolved multi-terahertz spectroscopy
Kuchařík, Jiří ; Němec, Hynek (advisor) ; Pereira, Mauro Fernandes (referee) ; Richter, Ivan (referee)
Terahertz conductivity spectra contain information on charge transport mechanisms and charge confinement on nanometer distances. In this thesis, we make a substantial progress in understanding of terahertz conductivity in several regimes. First, we theoretically investigate linear terahertz conductivity of confined electron gas: while the spectra of degenerate electron gas exhibit geometrical resonances, the response in non-degenerate case smears into a single broad resonance due to the wide distribution of charge velocities. Then, we theoretically and experimentally analyze various TiO2 nanotube layers: their linear charge transport properties strongly depend on the fabrication process, which influences the internal structure of the nanotube walls. In the main part of the thesis, we develop a framework for evaluation of the nonlinear terahertz response of semiconductor nanostructures based on microscopic Monte-Carlo calculations. The nonlinear regime is highly non-perturbative even in moderate fields as illustrated by efficient high harmonics generation. We investigate measurable nonlinear signals for various semiconductor nanostructures; metallic nanoslits filled with nanoelements are the most promising for the experimental observation of terahertz nonlinearities. These nonlinearities per unit charge are...
Simulations of light scattering from living cells
Vengh, Martin ; Richter, Ivan (referee) ; Petráček, Jiří (advisor)
Diplomová práca sa zaoberá rozptylom elektromagnetického žiarenia na biologickej bunke použitím metódy konečných diferencií v časovej oblasti (FDTD), Bornovej aproximácie a Rytovovej aproximácie. Metóda FDTD dáva presné výsledky v širokej škále problémov. Je spravené porovnanie Bornovej aproximácie a Rytovovej aproximácie prostredníctvom FDTD metódy. Ďaľšia časť práce zahrnuje krátky popis koherenciou riadeného holografického mikroskopu CCHM. Záverečná časť sa venuje zobrazeniu rozptýleného poľa získaného z jednotlivých simulácií pomocou simulácie objektového ramena mikroskopu CCHM.

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1 Richter, Igor
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