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Calculation of optical response of photonic structures by FDTD method
Vozda, Vojtěch ; Veis, Martin (advisor) ; Richter, Ivan (referee)
FDTD method is based on Maxwell's equations and this thesis describe how to make these differential equations computer readable for numerical solution known as the Yee algorithm. Time step dependence on spatial step is examined here in order to obtain stable solution. Discrete Fourier trasform is defined to obtain frequency dependent transmission and reflection coefficients. Programmed simulation is tested on analytically solvable structures even on slightly more complex systems whose optical response was computed by other type of simulation. Finally photonic crystals and their application as biosensors are discussed. Particular shape of photonic crystal is examined in details (frequency spectrum dependence upon spatial resolution, inaccuracy in geometry, different compounds in holes, geometry modification).
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Study of physical properties of nanostructures using magneto-optical techniques
Beran, Lukáš ; Veis, Martin (advisor) ; Mistrík, Jan (referee)
Magneto-optical spectroscopy methods are used to study magnetic pro- perties of materials down to nanometer dimensions due to its high sensiti- vity and non-contact nature. This requires sophisticated experimental setup, advanced technical equipment and precise optical components arrangement. This thesis describes the basic physical principles of magneto-optical Kerr spectroscopy. On the basis of these principles is designed and developed a new, much simpler experimental setup with crossed polarizers. This arran- gement has the same order of sensitivity and accuracy of measurement as commonly used modulation techniques to which it is compared in this work. Finally, this arrangement is applied to the study magneto-optical properties of selected magnetic structures and these properties are discussed. 1
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Study of physical properties of metallic nanostructures with induced magnetic anizotropy
Jesenská, Eva ; Veis, Martin (advisor) ; Kouřil, Karel (referee)
The aim of this thesis is a systematic study of physical properties of magnetic multilayered nanostructures. Namely it include multilayered spin valves NiFe/Cu/Co with magnetic anisotropy iduced by magnetic field applied during the deposition. Induced magnetic anisotropy influences exchange interactions between magnetic layers and so it gives the possibility to control magnetic properties of nanolayers. This is important for applications in MRAM, magnetoresistive read heads and spin-transfer-torque devices. Magnetooptic spectroscopy and Kerr effect hysteresis loop measurement were used as effective probe techniques. Secondly we examinated Ar3+ rf sputtering influence on multilayer interface quality level. We found out, that Ar3+ irradiation during deposition process has a possitive effect on interface quality.
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Design of Optically Detected Magnetic Resonance (ODMR) Spectrometer
Schneider, Martin ; Veis, Martin (referee) ; Neugebauer, Petr (advisor)
Diplomová práce se zabývá návrhem a sestavením nového spektrometru opticky detekované magnetické rezonance (ODMR) modifikací stávajícího spektrometru magnetického kruhového dichroismu (MCD) přivedením mikrovlnného ozařování. Je navrhnut nový držák vzorku umožnující osvětlení jak viditelným světlem, tak mikrovlnným zářením. Pro přivedení vlnění o nižších frekvencích je navržena anténa, určená k umístění pod vzorkem. Schopnosti celého systému jsou demonstrovány na sloučenínách kovových komplexů.
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Light propagation in magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor) ; Veis, Martin (referee)
Transparent magnetic materials, among the others semiconductors, have recently come to the focus of interest in both basic and applied research because they have great potential in optical applications and they can be used in optical spectroscopy to investigate fundamental physical phenomena. The theoretical calculations introduce that these materials have some extraordinary properties like asymmetric reflectance when light impact the sample from the opposite angles. In this bachelor thesis, transfer matrix formalism is derived based on Maxwell equations, taking into account special form of effective permittivity. The reflection coefficient for one layer demonstrates, that the asymmetric reflectance appears for transversal- magnetic polarization of light and transversal magnetization in the studied material. The derived formulae are used to calculate the difference in reflectivities for the waves impacting the structure from opposite angles. Ga1−xMnxAs with different concentrations of manganese is assumed to be the essential transparent magnetic layer in the sample. 1
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Magnetooptical spectroscopy of La2/3Sr1/3MnO3 ultrathin films
Zahradník, Martin ; Veis, Martin (advisor) ; Postava, Kamil (referee)
High quality La2/3Sr1/3MnO3 (LSMO) ultrathin layers are of interest for applications in magnetic sensors and spintronic devices due to colossal magnetoresistance of these materials. LSMO films studied in this thesis were grown by pulsed laser deposition on SrTiO3 substrates. The deposition at low oxygen pressures with the use of a beam homogenizer leads to the high quality LSMO films. The film thickness ranges from 5,0 to 103,9 nm. Magnetooptical (MO) spectrometer based on azimuth modulation was used and spectra of MO Kerr effect in polar and longitudinal configuration were obtained. All the spectra display features typical for LSMO films, including the thinnest 5 nm thick film. MO Kerr effect observed in this film reflects high magnetic ordering even at such low thickness. All the spectra manifest high quality of the LSMO films prepared with the use of the beam homogenizer.
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Advanced simulations of photonic structures by FDTD method
Vozda, Vojtěch ; Veis, Martin (advisor)
Finite-Difference Time-Domain method (FDTD) is based on numerical solution of Maxwell's equations, nowadays widely used for simulating optical response of photonic structures. This paper provides brief introduction to the FDTD method and several important extensions which make the basic code much more versatile. In order to broaden analysis of photonic structures, transfer matrix method (TMM) is also involved. The code is firstly tested using simple model structures which optical response might be compared with different numerical or even analytical approaches. Debugged code is used to improve photonic crystals for enhanced sensitivity of biosensing devices based on refractive index changes of sensed medium. Last but not the least, properties (sensitivity and Q-factor of resonant peak) of holey waveguide are investigated in one-, two- and three-dimensional simulation. It is shown here, that even this simple structure may compete with complex photonic crystals in the field of biosensors. Powered by TCPDF (www.tcpdf.org)
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Magneto-optical spectroscopy of perovskites thin films with colossal magnetoresistence
Veis, Martin
Najzev prace: Magneto-opticka spektroskopie tenkych vrstev perovskitu s kolosalm mag- netorezistenci Autor: Martin Veis Katedra (ustav): Fyzikalni ustav Univerzity Karlovy Vedouci diplomove prace: Prof. Ing.Stefan ViSnovsky, DrSc. e-mail vedouciho: visnov@karlov.mff.cuni.cz Abstrakt: Magnetoopticka spektra perovskitu s zelezitymi kationty v oblasti od 2 do 6 eV se vyznacuji bohatou strukturou a ostrymi liniemi. Jejich elektricky odpor je vysoky. To je zpusobeno existenci jedineho typu kationtu s peti elektrony na hladinach 3d, ktery se naleza v centru kyslikoveho oktaedru se shizenou symetrii. Nahrada zelezitych iontu ionty Mn s ruznou valenci mem radikalne elektricky odpor i krystalografickou symetrii a nutne musi nalezt odraz i v optickych vlastnostech. Ty nebyly zatim na tenkych vrstvach pfipraven}^ch pulzni laserovou depozici systematicky studovany. Diplomova prace je ve- novana magnetoopticke spektroskopii tenkych vrstev v oblasti 1 az 5 eV v zavislosti na tloust'ce v mezich od 20 do 60 nm s cilem pfispet novymi poznatky o elektronove struktufe techto vrstev. Klifiova slova: Kerruv magnetoopticky jev, Laz/sSri/sMnOs, Pulzni laserova depozice Title: Magneto - optical spectroscopy of perovskites thin films with colossal magnetore- sistence Author: Martin Veis Department: Institute of Physics, Charles...
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