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High-average power picosecond mid-IR source
Vyvlečka, Michal ; Novák, Ondřej (advisor) ; Trojánek, František (referee)
1 Title: High-average power picosecond mid-IR source Author: Michal Vyvlečka Department: Department of Chemical Physics and Optics Supervisor: Ing. Ondřej Novák, Ph.D., Hilase centre, Institute of Physics of CAS Abstract: High average power wavelength tunable picosecond mid-IR source based on optical parametric generation (OPG) and optical parametric amplification (OPA) is being developed. The conversion system is pumped by an Yb:YAG thin-disk laser delivering 100 W of average power at 100 kHz repetition rate, 1030 nm wavelength, and 2-3 ps pulse width. Part of this fundamental beam pumps an OPG process in a PPLN crystal. The generated wavelength is determined by PPLN's poling period and temperature. Tunability of the signal wavelength between 1.46 µm and 1.95 µm was achieved, the signal beam of 20 mW was generated at 2 W of pump power, when double pass of the beams through PPLN crystal was used. The corresponding idler wavelengths were in range 2.18-3.50 μm. The signal beam was further amplified by OPA process in two KTP crystals, which was pumped by the fundamental beam. The signal beam was amplified up to 2 W at pumping of 38 W. Tuning of the output wavelength was realized by change of the phase-matching angle in KTP crystals. Tunability between 1.70-1.95 µm for signal and 2.18-2.62 µm for idler was...
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Ultrafast laser spectroscopy of semiconductor nanostructures
Chlouba, Tomáš ; Trojánek, František (advisor)
In this work we investigate changes in dynamics of CdSe nanocrystalline films caused by different annealing temperatures and different conditions during films growth. We use methods of time-resolved laser spectroscopy like time-resolved pump and probe and streak camera to study these dynamics. We also measured linear absorption and luminiscence. Our goal is to match measured dynamics with dynamics of other samples with different annealing temperatures and discuss the microscopic origin of these dynamics. Powered by TCPDF (www.tcpdf.org)
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Laser spectroscopy of crystalline and nanocrystalline diamond
Zukerstein, Martin ; Trojánek, František (advisor) ; Preclíková, Jana (referee)
The aim of this thesis is a study of NV centres in crystalline and nanocrystalline diamond by laser spectroscopy methods. In the theoretical part we discuss the laser spectroscopy methods, the studied material - diamond and the NV colour centres. In the experimental part we discuss the influence of nanoparticle size on luminescence spectra. We measure the luminescence of samples at room and also at low temperatures depending on the intensity and wavelength of the excitation. We study the photo-conversion of negatively charged state of NV centres to the neutral in detail. We make the time resolved measurements of the luminescence on streak camera for characterization the dynamical properties of the studied samples. The result is the comparison of lifetimes of the states in NV centres in selected samples.
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Multiphoton absorption of ultrafast laser pulse
Zukerstein, Martin ; Trojánek, František (advisor) ; Schmoranzerová, Eva (referee)
Nonlinear optics is constantly developing and in terms of future applications very perspective field of physics. With high-intensity pulsed lasers we are able to study interesting phenomena in matter that we cannot observe with common sources of light. The aim of this thesis is a study of the multiphoton absorption of high-intensity pulses in diamond using z-scan technique. It theoretically describes this nonlinear phenomenon using quantum theory. The next section author took a measurement of the two-photon absorption and found the two-photon absorption coefficients in different samples. Diamond was chosen as the sample material. This material has absolutely unique properties that rank it highly in future applications for optoelectronic devices.
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Ultrafast laser spectroscopy of semiconductor nanostructures
Chlouba, Tomáš ; Trojánek, František (advisor) ; Žídek, Karel (referee)
In this work we investigate changes in dynamics of CdSe nanocrystalline films caused by different annealing temperatures and different conditions during films growth. We use methods of time-resolved laser spectroscopy like time-resolved pump and probe and streak camera to study these dynamics. We also measured linear absorption and luminiscence. Our goal is to match measured dynamics with dynamics of other samples with different annealing temperatures and discuss the microscopic origin of these dynamics. Powered by TCPDF (www.tcpdf.org)
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Time-resolved spectroscopy of semiconductor nanostructures
Kořínek, Miroslav ; Trojánek, František (advisor) ; Herynková, Kateřina (referee) ; Němec, Hynek (referee)
Title: Time-resolved spectroscopy of semiconductor nanostructures Author: RNDr. Miroslav Kořínek Department: Department of Chemical Physics and Optics Supervisor: doc. RNDr. František Trojánek, Ph.D., Department of Chemi- cal Physics and Optics, Faculty of Mathematics and Physics, Charles University in Prague Abstract: This Ph.D. thesis is focused on the study of relaxation and re- combination processes in silicon nanocrystals embedded in dielectric (SiO2, SiC and Si3N4) matrices that were fabricated within the EU 7th Framework Pro- gramme Silicon Nanodots for Solar Cell Tandem (NASCEnT). Different host ma- terials, in which silicon nanocrystals are incorporated, not only provide different transport properties, but also differently affect the nanocrystal surfaces. A large part of the thesis is devoted to research of SiO2-embedded silicon nanocrystals having various sizes (in the order of nanometers) and various inter-nanocrystal separation, that differ also in the manner of an additional annealing. Experimen- tal techniques of optical spectroscopy are used to monitor the photoexcited charge carrier dynamics on a wide time scale from picoseconds to milliseconds. The initial (picosecond) dynamics is characterized very well using a relevant rate equation. We propose a theoretical description of how the...
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Selection of femtosecond laser pulses
Bažíková, Sára ; Trojánek, František (advisor) ; Zázvorka, Jakub (referee)
Construction of the laser is one of the most important physical advances of modern times. Its use in practice is extremely common and desirable, therefore, it is necessary to push the boundaries of possibilities of this technique still further. Lasers generating ultrashort pulses are widely used in material research for the study of nonlinear effects and ultrafast processes. These lasers have a high repetition rate, which must be reduced for some applications. In this thesis we used femtosecond titanium -sapphire laser from Spectra Physics, whose repetition rate is 80 MHz. The aim of this thesis is to reduce this frequency by using a pulse selector. The key mechanism that utilizes the pulse selector is an acoustooptic modulator that is based on the principle of Bragg diffraction and it is able to select pulses with a frequency of 1 Hz-4 MHz. The end of thesis is measurement of the properties of this selector and its optimization.
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Modeling of optical bistability
Čerňanský, Robert ; Trojánek, František (advisor) ; Butkovičová, Dagmar (referee)
My work is dealing with nonlinear optical event called optical bistability or multistability which is expressed during an interaction of high-energetic laser beam with material. Optical bistability may occur in absortive coeficient or in refractive indice (or both). My work is more-less aimed as a theoretical experiment where I had predefined initial conditions and by the help of Microsoft Office Excel 2007 programm I have modeled the dispersive optical bistability for nanocrystalitc form of silicon dioxide and cadmium selenid. Powered by TCPDF (www.tcpdf.org)
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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.
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Optical properties of silicon nanostructures for photovoltaics
Salava, Jan ; Trojánek, František (advisor) ; Žídek, Karel (referee)
Název práce: Optické vlastnosti křemíkových nanostruktur pro fotovoltaiku Autor: Bc. Jan Salava Katedra: Katedra chemické fyziky a optiky Vedoucí diplomové práce: doc. RNDr. František Trojánek, Ph.D., katedra chemické fyziky a optiky Abstrakt: V předložené práci jsou studovány křemíkové nanokrystaly umístěné v SiC matrici - jednotlivé vzorky se odlišují přidáním dopantu (boru) do příslušné vrstvy struktury během depozice metodou PECVD a pasivací vodíkem. Křemíkové nanokrystaly jsou významné zejména tím, že oproti své objemové verzi vykazují účinnou fotoluminiscenci a absorpci ve viditelné oblasti spektra. Změnami parametr· při přípravě lze ladit jejich vlastnosti s ohledem na konkrétní aplikaci. Základní myšlenka integrace křemíkových nanostruktur do solárních článk· spočívá ve zvýšení účinnosti konverze slunečního spektra kombinací několika tenkých vrstev s nanokrystaly a objemového Si článku tak, aby každá vrstva sluneční cely absorbo- vala určitou část spektra. Procesy, které se v těchto strukturách dějí krátce po excitaci nosič· náboje, však stále nejsou zcela popsány. Cílem práce je charakterizace těchto jev· metodami ča- sově rozlišené spektroskopie. Dalším úkolem je popsat vliv dopování jednotlivých částí materiálu a jeho pasivace ve vodíkové atmosféře na chování fotoexcitovaných nosič· a intenzitu...
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