National Repository of Grey Literature 62 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Generation of harmonic frequencies of the high-power picosecond laser beam
Šatra, Šimon ; Novák, Ondřej (advisor) ; Trojánek, František (referee)
This work is dedicated to the generation and characterization of beams of harmo- nic frequencies of the Perla C-100 laser. In the theoretical part, coupled wave equations are derived with application to the generation of second harmonic and sum frequency, and a comparison of other systems for the generation of harmonic frequencies is made. The second part is dedicated to the design of the system for the generation of harmonic frequencies, the choice of suitable nonlinear crystals, and numerical simulations are used to determine the ideal parameters of the given crystals. The experimental part describes the set-up for the generation of harmonic frequencies, characterizes the important beam parameters, namely powers, pulse lengths, pulse spectra, M2 parameters and beam pro- files, and adresses the effect of changing the repetition frequency of laser pulses on the generation of harmonic frequencies. 1
Study of electric fields in silicone carbide
Sanitrák, Jakub ; Dědič, Václav (advisor) ; Trojánek, František (referee)
Silicon carbide (SiC) is due to its unique electrical and mechanical properties very important material for photonics and electronics. Hexagonal polytypes of SiC are being used as substrates for the growth of epitaxial graphene. SiC shows Pockels linear electro- optic effect. The goal of this thesis was to use Pockels effect and evolve the method to study profiles of inner eletric fields and accumulations of electric charges inside SiC, whose variations may influence functions of optoelectronic components. Our method con- sists in complex evaluation of optical transmittances of crystals inserted between crossed polarizers. It has been shown that the excitation light with photon energy near the ban- dgap of SiC significantly influences profiles of inner electric field due to accumulation of photogenerated charge on traps. The conclusion of the thesis concentrates mainly on the discussion of causes affecting the accuracy of this new method. 1
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)
Ultrafast laser spectroscopy of semiconductor nanostructures
Neudert, Karel ; Trojánek, František (advisor) ; Nikl, Martin (referee) ; Herynková, Kateřina (referee)
This doctoral thesis deals with analysis of carrier dynamics in semiconductor nanocrystals and nanostructures by methods of ultrafast laser spectroscopy. In three chapters silicon, InAs/GaAs, InAs/AlAs and CdSSe materials are studied. Silicon nanocrystals prepared by sol-gel method were measured by time-resolved luminescence method with various time resolutions, two-photon absorption and Z-scan method. A model describing findings was suggested. InAs was well measured by upconversion method and gained knowledge appeared to be fully consistent with quantum model. CdSe material was examined in two basic forms - thin films of nanocrystals prepared by chemical deposition and nanocrystals in comercial filters. In both cases all questions regarding influencing optical properties of nanocrystals by modification of their growth were answered.
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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