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Ultrafast generation of anisotropic electron population in conduction band of semiconductors
Čmel, Martin ; Kozák, Martin (advisor) ; Dzurňák, Branislav (referee)
The thesis is devoted to a possible implementation of a new concept of electronics, the so-called valley-tronics, on an experimental optical setup. The aim is the construction of this setup that enables the study of the generation and detection of anisotropic distribu- tion of electrons in conduction band of diamond by means of interaction with ultrashort laser pulses. After understanding the topic, an optical setup based on an extended pump and probe method is assembled. The first pulse excites the electron population. A second pulse arriving with a given time delay accelerates the electrons and generates an aniso- tropic population in the conduction band. The generated anisotropy is measured by the third, probe pulse, with which the polarization anisotropy of the transient absorption is detected. As a part of the thesis, preliminary measurements are evaluated and the depen- dence of the relaxation time of valley polarization in diamond on the setup parameters is interpreted. This valley polarization could be used in the aforementioned valley-tronics, in which information would not be carried by charge, but by the electron valley number.
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Quantum statistics and coherence of photons emitted by optically modulated electron beams
Kuchař, Marek ; Kozák, Martin (advisor) ; Konečná, Andrea (referee)
The interaction of swift electrons with matter is used to study and image the struc- ture of materials in the field of electron microscopy and diffraction. One particular form of this interaction is the emission of a photon due to the coupling of the electron's elec- tromagnetic field with the polarization of the material in its vicinity, a phenomenon called cathodoluminescence. Recent theoretical works predict that it might be possible to observe the optical coherence imprinted upon the electron wavefunction by modulation through optical fields in the coherence properties of the emitted photons. In this thesis, we extend the theoretical formalism currently used to study this effect in order to gain a deeper understanding by studying different regimes of optical modulation of the electron beam. In the first chapter of this thesis, we discuss important aspects of electron-matter interaction arising from classical electrodynamics, and in the second chapter, we sys- tematically construct a quantum electrodynamic formalism for studying the statistical properties of emitted photons. By using simple numerical simulations, we then visualize the expected dependence of their degree of coherence on relevant physical parameters based on derived analytical results. 1
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Ultrafast dynamics of charge carriers in 2D materials
Koutenský, Petr ; Kozák, Martin (advisor)
Title: Ultrafast dynamics of charge carriers in 2D materials Author: Bc. Petr Koutenský Department: Department of Chemical Physics and Optics Supervisor: RNDr. Martin Kozák, Ph.D., Department of Chemical Physics and Optics Abstract: The goal of this thesis was to study ultrafast dynamics of excitons in monolayers of transient metal dichalcogenides WSe2 and MoS2 using methods of ultrafast laser spectroscopy. We focus on two types of processes in this thesis. We measured ultrafast dynamics of carrier recombination and inter-valley scattering of excitons. We also focused on ultrafast manipulation with excitonic energy levels which allows us to remove the energy degeneracy in different minima of the band structure using coherent optical effects (optical Stark effect and Bloch-Siegert shifts). In the future, the observed phenomena could contribute to developement of new utrafast optical and optoelectronical devices exploting so called valley polarization of electrons in the studied materials. Keywords: Ultrashort laser puses, time-resolved laser spectroscopy, nonlinear op- tics, 2D crystals iii
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Generation of high harmonic frequencies in crystalline materials
Gindl, Adam ; Kozák, Martin (advisor) ; Veselá, Petra (referee)
The interaction of intense ultrashort laser pulses with materials in the strong field regime of nonlinear optics enables the study of electron excitations with high temporal resolution. In this thesis, we focus on the experimental research of high harmonic ge- neration in crystalline silicon. The goal of our study is to reach the modulation of the amplitude and the phase of the generated field using coherence control by a superposition of optical fields at the fundamental and its third harmonic frequency. The modulation of the generated field occurs due to the change of the relative phase shift between the driving fields. The resulting amplitude and phase changes of the high harmonic field are investi- gated for different amplitude ratios of the driving fields using spectroscopic methods and spectral interferometry. The newly introduced spectral interferometry technique enables the measurement of the emission delay of high-energy photons on attosecond time scale. 1
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Suricata Module for IBM QRadar
Kozák, Martin ; Žádník, Martin (referee) ; Hranický, Radek (advisor)
This work integrates the Suricata program into the QRadar system. The main objective of this work is to design and implement a DSM module in QRadar system that can analyze the records from Suricata. The events can then be investigated in the QRadar system environment. Another objective is to design an application that displays the data detected by the Suricata program. The application can be installed in the QRadar environment and used with other built-in components. The application is programmed in the Flask library using Jinja2 templates. The application includes two tabs that display events in different graphs and table.
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The importance and use of wetland plants in the past and present times
KOZÁK, Martin
This paper deals with a research on the importance and use of wetland plants in history and present. The aim of the work is to collect information and critically assess the information on the importance of wetland plants to human society in the past and present including their uses. The review builds on the existing treatment of the topic in the Czech language and extends it with information published in foreign-language scientific and professional literature over the last 20 years and summarizes knowledge especially on wetlands, useful, invasive and endangered wetland plants.
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Classical and quantum model of 1D dynamics of free electron in ponderomotive potential of an optical beat wave
Kuchař, Marek ; Kozák, Martin (advisor) ; Chlouba, Tomáš (referee)
Inelastic scattering of freely propagating electrons on light waves is currently a studied topic because of potential applications in advanced electron microscopy and diffraction. The interaction is typically described using an approximation, in which we assume that the electron's velocity nearly does not change during the interaction. In this thesis we aim to describe the dynamics of electrons in an interaction potential generated by an optical wave beyond this regime. In classical description we solve the nonlinear equation of motion and while addressing the problem using quantum mechanical description we first use parabolic approximation of the interaction potential and then we also study the evolution of a free electron wavefunction in a full periodic potential. Using numerical simulations we show the expected evolution of the electron spectra during the interaction, based on analytical solutions. 1
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Generation of femtosecond supercontinuum using ultrashort laser pulses with stable carrier-envelope phase
Harabišová, Jana ; Kozák, Martin (advisor) ; Žídek, Karel (referee)
Femtosecond supercontinuum is a nearly ideal source of light for optical spectroscopy due to its extremely broad spectrum and a combination of high temporal and spatial coherence. This thesis is focused on experimental study of supercontinuum generation by ultrashort laser pulses in the mid-infrared spectral region, which belongs to the area of anomalous dispersion regime in most of optical materials. The self-compression of the pulse propagating through the material causes not only extreme spectral broadening but also generation of the so-called dispersive wave. The objective of this thesis is to observe and study the dependence of the generated spectra of the visible light on the absolute phase of the pulse, which is stabilized thanks to the technique of generation of the input pulse based on difference frequency generation. Selected measurements are compared with numerical solution of one dimensional generalized non-linear Schrödinger equation. 1
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Ultrafast dynamics of charge carriers in 2D materials
Koutenský, Petr ; Kozák, Martin (advisor) ; Galář, Pavel (referee)
Title: Ultrafast dynamics of charge carriers in 2D materials Author: Bc. Petr Koutenský Department: Department of Chemical Physics and Optics Supervisor: RNDr. Martin Kozák, Ph.D., Department of Chemical Physics and Optics Abstract: The goal of this thesis was to study ultrafast dynamics of excitons in monolayers of transient metal dichalcogenides WSe2 and MoS2 using methods of ultrafast laser spectroscopy. We focus on two types of processes in this thesis. We measured ultrafast dynamics of carrier recombination and inter-valley scattering of excitons. We also focused on ultrafast manipulation with excitonic energy levels which allows us to remove the energy degeneracy in different minima of the band structure using coherent optical effects (optical Stark effect and Bloch-Siegert shifts). In the future, the observed phenomena could contribute to developement of new utrafast optical and optoelectronical devices exploting so called valley polarization of electrons in the studied materials. Keywords: Ultrashort laser puses, time-resolved laser spectroscopy, nonlinear op- tics, 2D crystals iii
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