National Repository of Grey Literature 12 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
Terahertz radiation in nanostructures
Hendrych, Erik ; Ostatnický, Tomáš (advisor) ; Kozák, Martin (referee)
We explore conductivity of nanostructures in the terahertz range. We model the nanostructure as a square potential well with a barrier inside. We examine how the conductivity depends on temperature, material constants and dimensions of the potential well. The conductivity of the material determines the complex refractive index and thus influences its optical properties such as reflexivity, transmittance and attenuation coefficient. We construct the functional dependency of the conductivity on the electric field frequency. The maxima of this functional dependency correspond to spectral lines. We examined the dependency of the frequencies of the maxima (spectral lines) on various parameters. We got the most interesting result when we continuously changed the position of the barrier inside the potential well. For different heights of the barrier we got qualitatively different results. With high barrier the system behaves as two separate potential wells where we can see monotonous functional dependency of the spectral lines on the position of the barrier. With low potential barrier we get oscillating dependencies. For gallium arsenide and 2 nm width of the potential barrier, high barrier is higher than 1 eV, while low barrier is lower than 0, 05 eV.
Novel technique for characterization of ultrashort optical pulses
Peterka, Pavel ; Kozák, Martin (advisor) ; Ostatnický, Tomáš (referee)
Ultrashort laser pulses are nowadays widely used in both the basic and applied reseach as well as in a wide range of applications. Application of laser pulses requires their complete characterization from the point of view of temporal evolution of field amplitude and frequency on femtosecond timescales. This thesis is focused on a new method for ultrashort pulse characterization, which involves measuring spectral interference between input pulse and the pulse transmitted through a medium with cubic nonlinear susceptibility. The new method is inte- resting compared to the established techniques mainly because of its simplicity, as it requires only one medium with cubic nonlinear susceptibility and a spectro- meter. We have implemented the technique experimentally and determined pulse duration and phase for ideally compressed pulse.
Knowledge of rowing between students of Faculty of Physical Education and Sport, Charles University and Faculty of Physical Culture Palacký University Olomouc
Richterová, Nikol ; Janák, Vladimír (advisor) ; Kozák, Martin (referee)
Title: Knowledge of rowing between students of Faculty of Physical Education and Sport - Charles University and Faculty of Physical Culture - Palacký University Olomouc Objectives: The main objective of this work is research on the extent of knowledge about rowing of the students of two sports-oriented university faculties. Another aim is to compare general knowledge of students and comparison of the two selected faculties Methods: To determine the necessary information was used quantitative research, using on-line interviews. Before the interview was modified a questionnaire on the given subject, which was planned for 100 respondents. The research was conducted using an electronic questioning when the questionnaire was completed 119 respondents from Faculty of Physical Education and Sport - Charles University and The Faculty of Physical Culture - Palacký University Olomouc Results: Based on the research results, it is possible to say that knowledge and awareness about the rowing is among respondents rather average. Approximately 75 % of the respondents knew the correct answer in three questions. But to another question stated the right answer only 12 % of respondents. After mutual comparison of the two faculties, it is possible to say that knowledge of rowing are comparable. Keywords: rowing,...
Sum-frequency generation in far-UV spectral region
Martínek, Miroslav ; Kozák, Martin (advisor) ; Ondič, Lukáš (referee)
Nonlinear optics is the area of high field optics, where the dependence of polarization of matter on the electric field of optical radiation cannot be considered as linear. This has important implications for practise, since the superposition principle is no longer valid in nonlinear optics. Thus it is possible to influence light, propagating through material, by another intensive radiation. Nonlinear optical phenomena are important especially for laser technology because they allow to generate light at different wavelengths using various interactions. This thesis is focused on the study of the sum-frequency generation in the far ultraviolet (UV) region of the spectrum. As the radiation source the femtosecond laser system was used. The aim of the study was to theoretically describe generation by nonlinear wave equation and to calculate the dependence of phase-matching angle on generated wavelength. Theoretical results were then verified experimentally in the laboratory. Also the energy of generated pulses and sum-frequency generation efficiency were measured for pulses in spectral region 215-250 nm. The generated pulses will further serve to excite electron-hole pairs in the diamond.
Studium optických nelinearit v polovodičích a polovodičových nanostrukturách
Kozák, Martin ; Trojánek, František (advisor) ; Herynková, Kateřina (referee) ; Kužel, Petr (referee)
This Ph.D. thesis is focused on the study of optical nonlinearities and dynamics of excited charge carriers in monocrystalline diamond, nanocrystalline diamond and silicon. The dynamics of high density carriers in bulk diamond is investigated in detail (the transition from excitons and free carriers to electron-hole liquid or plasma). We study the picosecond dynamics of electron-hole liquid condensation using several techniques of time-resolved optical spectroscopy and demonstrate its evaporation by femtosecond laser pulses. We also propose two new optical techniques for measurement of lifetime, diffusion coefficient and surface recombination velocity of excitons in diamond. The results obtained by these techniques are described theoretically using diffusion equation and compared with the results obtained by the transient grating diffraction measurement. Further we study two- and three- photon absorption and nonlinear refractive index in diamond. In nanocrystalline diamond we study the second and third harmonic generation and its physical origin. In superlattices of silicon nanocrystals in SiO2 matrix we investigate the nonlinear transient absorption dynamics and carrier diffusion.
Time-resolved laser spectroscopy of nanomaterials
Kozák, Martin
Title: Time-resolved laser spectroscopy of nanomaterials: Study of nonlinearities using z-scan method Author: Martin Kozák Department: Department of chemical physics and optics Supervisor: Doc. RNDr. František Trojánek, Ph.D. Supervisor e-mail adress: Frantisek.Trojanek@mff.cuni.cz Abstract: This diploma thesis is oriented to study of nonlinear properties in semiconductor nanocrystals using ultrashort femtosecond pulses. There is a detailed description of theory and experimental setup of the z-scan method, which can be used to measure the nonlinear refractive index and two-photon absorption coefficient. In the theoretical part we describe the influence of measurement by quality of laser beam, quality and thickness of the sample. There are numerical simulations of measurements influenced by these parameters. This theory is used for processing of measured dates by a simple program, which is attached to this thesis on CD. In experimental part we were measured nonlinear refractive indeces of diamond nanocrystals fabricated by the PECVD method, silicon and CdS nanocrystals in glass matrices. One part of this thesis was also the preparation and optimalization of experimental setup and increasing the signal/noise ratio. Keywords: Z-scan, Kerr effect, nonlinear refractive index, two-photon absorption, nanocrystals
Time-resolved laser spectroscopy of nanomaterials
Kozák, Martin ; Šimurda, Miroslav (referee) ; Trojánek, František (advisor)
This diploma thesis is oriented to study of nonlinear properties of semiconductor nanocrystals using ultrashort femtosecond pulses. There is a detailed description of theory and experimental setup of the z-scan method, which can be used to measure the nonlinear refractive index and the two-photon absorption coefficient. In theoretical part we describe the influence the quality of laser beam, quality and thickness of the sample on measurements. There are numerical simulations of the measurements influenced by these parameters. This theory is used for processing of the measured dates by a program, which is attached to this thesis on CD. In experimental part we measured nonlinear refractive indeces of diamond nanocrystals fabricated by the PECVD method, silicon and CdS nanocrystals in glass matrices. One part of this thesis deals with the preparation and optimalization of the experimental setup and increasing the signal/noise ratio.

National Repository of Grey Literature : 12 records found   1 - 10next  jump to record:
See also: similar author names
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5 Kozák, Michal
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1 Kozák, Miroslav
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