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Spatially- and time-resolved laser spectroscopy
Kuchařík, Jiří ; Němec, Petr (advisor) ; Preclíková, Jana (referee)
Speed is one of the most important characteristics of the majority of electro- nic and optoelectronic components. Ultrafast laser spectroscopy is therefore a very effective tool for studying the properties of materials suitable for their pro- duction. However, for more detailed information it is also necessary to achieve a high spatial resolution. In this bachelor thesis we deal with several experimental approaches which allow us to achieve a high spatial resolution in time-resolved experiments. In particular, we describe experimental setups using microscope ob- jectives and we also mention the use of transient grating technique. Furthermore, we present the results of our measurement of a time length of ultrashort laser pulses which are generated by the pulse laser Mai Tai HP and their expansion due to propagation through microscope objectives. 1
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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...
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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...
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Investigation of spin polarization by laser spectroscopy
Kuchařík, Jiří ; Němec, Petr (advisor) ; Veis, Martin (referee)
Spintronics is a new branch of electronics, which uses not only the charge of electron but also its spin for transfer and processing of information. For re- al applications it is necessary to understand, how the magnetic state of matter changes not only in time but also in space. This diploma thesis is therefore de- voted to the imaging of magnetic domains in ferromagnetic semiconductors by purely optical methods, which are based on the usage of the magneto-optical ef- fects. In first part of the thesis we concentrated on the optimalization of existing polarizing microscope, whose function is based solely on the polar Kerr effect. After the optimalization we try to use this setup to observe magnetic domains in ferromagnetic semiconductor GaMnAs by the means of the magnetic linear dichroism. 1
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Spatially- and time-resolved laser spectroscopy
Kuchařík, Jiří ; Němec, Petr (advisor) ; Preclíková, Jana (referee)
Speed is one of the most important characteristics of the majority of electro- nic and optoelectronic components. Ultrafast laser spectroscopy is therefore a very effective tool for studying the properties of materials suitable for their pro- duction. However, for more detailed information it is also necessary to achieve a high spatial resolution. In this bachelor thesis we deal with several experimental approaches which allow us to achieve a high spatial resolution in time-resolved experiments. In particular, we describe experimental setups using microscope ob- jectives and we also mention the use of transient grating technique. Furthermore, we present the results of our measurement of a time length of ultrashort laser pulses which are generated by the pulse laser Mai Tai HP and their expansion due to propagation through microscope objectives. 1
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