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Study of optical nonlinearities in semiconductors and semiconductor nanostructures
Chlouba, Tomáš ; Trojánek, František (advisor) ; Filip, Radim (referee) ; Herynková, Kateřina (referee)
In the main part of this thesis I study the relaxation mechanisms of charge carriers in silicon nanocrystals in SiO2 matrix. One of the potential applications of these structures lies in photovoltaics, specifically in construction of all-silicon tandem solar cells. I studied the dynamics of carriers in these structures by methods of ultrafast spectroscopy which helped to unravel the microscopic behaviour of carriers, their transport, localization etc. Furthermore I investigated the doping of such structures as the technology of doping is crucial for manufacture of pn- junctions which are the core component of solar cells. At the end I delve into the dissipative Jaynes-Cummings model by mathematical modeling and theoretical calculations which describes among others microlasers and as such comes under a field of cavity quantum electrodynamics.
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Study of properties of ultrashort femtosecond pulses
Hamráček, Karol ; Trojánek, František (advisor) ; Surýnek, Miloslav (referee)
Title: Study of the properties of ultra-short femtosecond pulses Author: Karol Hamráček Department: Department of chemical physics and optics Supervisor: doc. RNDr. František Trojánek, Ph.D. Abstract: Even as a bachelor thesis, the ultra-short pulses produced by the Rainbow CEP4 PRo laser system are about 7 fs long. This implies a very wide spectrum of these pulses, which can be up to 300 nm wide. This is why the ultrashort pulse will be lengthen by passing through a common dispersive medium such as the optical system of the classical optical elements, since each wavelength in the spectrum will propagate differently in the environment and will therefore overtake each other, resp. they will lag behind each other. Our aim will be to study this issue and to deal with the behavior of ultra-short pulses in different media. Keywords: ultra-short pulse, UV area, second harmonic wave
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Time-resolved spectroscopy of wide-bandgap semiconductors
Martínek, Miroslav ; Trojánek, František (advisor)
In this thesis experimental samples of multiple quantum wells in the InGaN/GaN structures will be compared using methods of laser spectroscopy. In particular, the optical properties of the samples will be investigated. The samples were prepared under different conditions; therefore one of the aims is to compare them. The knowledge of the influence of preparation enables utilization not only for fundamental research, but also for the construction of radiation sources or scintillation detectors. Measurements of absorption and photoluminescence will be carried out and their dynamic properties will be measured as well. There will be examined the effect of different excitation power and different excitation wavelength on the intensity of photoluminescence. From dynamic properties there will be examined the effect of different excitation wavelength on the lifetime of the absorption and how does temperature influence the lifetime of the photoluminescence. Individual quantities will be compared amongst samples and their suitability for further applications will be discussed.
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Laser spectroscopy of crystalline and nanocrystalline diamond
Zukerstein, Martin ; Trojánek, František (advisor)
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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Time-resolved spectroscopy of wide-bandgap semiconductors
Martínek, Miroslav ; Trojánek, František (advisor) ; Žídek, Karel (referee)
In this thesis experimental samples of multiple quantum wells in the InGaN/GaN structures will be compared using methods of laser spectroscopy. In particular, the optical properties of the samples will be investigated. The samples were prepared under different conditions; therefore one of the aims is to compare them. The knowledge of the influence of preparation enables utilization not only for fundamental research, but also for the construction of radiation sources or scintillation detectors. Measurements of absorption and photoluminescence will be carried out and their dynamic properties will be measured as well. There will be examined the effect of different excitation power and different excitation wavelength on the intensity of photoluminescence. From dynamic properties there will be examined the effect of different excitation wavelength on the lifetime of the absorption and how does temperature influence the lifetime of the photoluminescence. Individual quantities will be compared amongst samples and their suitability for further applications will be discussed.
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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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