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Femtosecond absorption spectroscopy for study of stimulated emission
Streshkova, Neli ; Malý, Petr (advisor) ; Zukerstein, Martin (referee)
The aim of the thesis is the building and optimization of an experimental setup for me- asuring the transient transmission and optical gain by the femtosecond pump and probe technique. The setup combines the technology of parametric generation of pump pulses with tunable wavelength and the generation of femtosecond continuum as a spectrally wide probe. In the thesis, conditions of supercontinuum generation in bulk fused silica are extensively studied from a practical viewpoint. The performance of the setup was tested on two types of samples: the solution of rhodamine 6G in methanol and the semiconduc- tor nanocrystalline sample - CdSSe-doped glass. Time resolved spectra of the transient transmission of both samples were measured and the spectral dependence of the optical gain in rhodmine 6G was obtained. 1
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Time-resolved measurement of optical gain in silicon based nanostructures
Ondič, Lukáš
2 Title: Time-resolved measurement of optical gain in silicon based nanostructures Author: Bc. Lukáš Ondič Department: Department of Chemical Physics and Optics Supervisor: Prof. RNDr. Ivan Pelant, DrSc., Institute of Physics, Academy of Sci- ences of the Czech Republic Supervisor's email address: pelant@fzu.cz Abstract: The aim of this work is to study the optical properties of the mate- rial based on oxidized silicon nanocrystals (Si-ncs) embedded at high densities in SiO2-based matrix. These materials seem to be very promising on the way towards silicon laser. Using our preparation technique - modified electrochemical etching and post-etching in H2O2 - we obtain small Si-ncs with the mean core size of 2-3 nm, in- corporated at high densities of ∼ 1019 Si-ncs/cm3 into an SiO2-based matrix. In this work, we focused on studying their photoluminiscence (PL) properties and measuring the net optical gain of these samples. Therefore, we investigated their time-resolved and steady-state PL emission spectra which revealed two emission bands - the F-band (∼ 435 nm) with ns decay-time and the S-band (∼ 600 − 620 nm) with µs decay- time. Moreover, we observed a "green" emission band (∼ 500 nm) present only during the pulsed excitation and immediately after. We performed time-resolved gain spec- troscopy using...
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Femtosecond absorption spectroscopy for study of stimulated emission
Streshkova, Neli ; Malý, Petr (advisor) ; Zukerstein, Martin (referee)
The aim of the thesis is the building and optimization of an experimental setup for me- asuring the transient transmission and optical gain by the femtosecond pump and probe technique. The setup combines the technology of parametric generation of pump pulses with tunable wavelength and the generation of femtosecond continuum as a spectrally wide probe. In the thesis, conditions of supercontinuum generation in bulk fused silica are extensively studied from a practical viewpoint. The performance of the setup was tested on two types of samples: the solution of rhodamine 6G in methanol and the semiconduc- tor nanocrystalline sample - CdSSe-doped glass. Time resolved spectra of the transient transmission of both samples were measured and the spectral dependence of the optical gain in rhodmine 6G was obtained. 1
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Silicon nanocrystals, photonic structures and optical gain
Ondič, Lukáš ; Herynková, Kateřina (advisor) ; Oswald, Jiří (referee) ; Lauret, Jean-Sebastien (referee)
Silicon nanocrystals (SiNCs) of sizes below approximately 5 nm are a material with an efficient room-temperature photoluminescence (PL) and optical gain. Optical gain is a pre- requisite for obtaining stimulated emission from a pumped material, and the achievement of stimulated emission (and lasing) from Si-based nanostructures is of particular interest of the field of silicon photonics. The aim of this work was (i) to investigate fundamental optical properties of SiNCs, (ii) to design and prepare a photonic crystal with enhanced light ex- traction efficiency and (iii) to explore a possibility of enhancing optical gain of light-emitting SiNCs by combining them with a two-dimensional photonic crystal. First, free-standing oxide (SiOx/SiO2)-passivated SiNCs were prepared by electrochemical etching of a Si wafer. Their optical properties were studied by employing time-resolved spectroscopy, also at cryogenic temperatures. The fast blue-green emission band of these SiNCs was linked with the quasi- direct recombination of hot electrons and holes in the vicinity of the Γ-point. Furthermore, the spectral shift of the slow orange-red band (of these SiNCs) as a function of temperature was explained on the basis of an interplay between tensile strain and bulk Si temperature-induced indirect bandgap shift. The...
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Time-resolved measurement of optical gain in silicon based nanostructures
Ondič, Lukáš
2 Title: Time-resolved measurement of optical gain in silicon based nanostructures Author: Bc. Lukáš Ondič Department: Department of Chemical Physics and Optics Supervisor: Prof. RNDr. Ivan Pelant, DrSc., Institute of Physics, Academy of Sci- ences of the Czech Republic Supervisor's email address: pelant@fzu.cz Abstract: The aim of this work is to study the optical properties of the mate- rial based on oxidized silicon nanocrystals (Si-ncs) embedded at high densities in SiO2-based matrix. These materials seem to be very promising on the way towards silicon laser. Using our preparation technique - modified electrochemical etching and post-etching in H2O2 - we obtain small Si-ncs with the mean core size of 2-3 nm, in- corporated at high densities of ∼ 1019 Si-ncs/cm3 into an SiO2-based matrix. In this work, we focused on studying their photoluminiscence (PL) properties and measuring the net optical gain of these samples. Therefore, we investigated their time-resolved and steady-state PL emission spectra which revealed two emission bands - the F-band (∼ 435 nm) with ns decay-time and the S-band (∼ 600 − 620 nm) with µs decay- time. Moreover, we observed a "green" emission band (∼ 500 nm) present only during the pulsed excitation and immediately after. We performed time-resolved gain spec- troscopy using...
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Nonlinear optical properties of silicon nanostructures
Žídek, Karel ; Trojánek, František (advisor) ; Bryknar, Zdeněk (referee) ; Kuldová, Karla (referee)
Název práce: Nelineární optické vlastnosti křemíkových nanostruktur Autor: Karel Žídek Katedra (ústav): Katedra chemické fyziky a optiky Vedoucí disertační práce: Doc. RNDr. František Trojánek, Ph.D. E-mail vedoucího: trojanek@karlov.mff.cuni.cz Abstrakt: Disertační práce se zabývá nelineárními optickými jevy a ultrarychlým vývojem luminis- cence křemíkových nanokrystalů. Pomocí metody optického hradlování signálu (časové rozlišení až 250 fs) porovnáváme ultrarychlý vývoj luminiscence křemíkových nanokrystalů s různými ve- likostmi (v řádu jednotek nanometrů) a také s rozdílnými formami pasivace. Pro nanokrystaly, kde po excitaci dominuje vliv zachytávání nosičů do povrchových stavů nanokrystalu, navrhujeme teoretický popis závislosti rychlosti těchto procesů na vlastnostech nanokrystalů. Dále v práci podrobně zkoumáme působení Augerovy rekombinace, která se projevuje jak v časově rozlišené, tak i v časově integrované emisi vzorků. Experimentální data velmi dobře popisuje námi navržený model na bázi kinetických rovnic. Závěr práce se zaměřuje na zkoumání ultrarychle dohasínající stimulované emise. U stávajících metod měření optického zisku (VSL a SES) navrhujeme jejich rozšíření pro...
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