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Development of a non-collinearly phase matched optical parametric amplifier and application in pump-probe spectroscopyRohwer, Egmont J. 03 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2011. / Please refer to full text to view abstract.
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Femtosecond pump probe spectroscopy of light harvesting complexes and PhthalocyaninesOmbinda-Lemboumba, Saturnin 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The generation of ultrafast light pulses and the development of time resolved
spectroscopic techniques, such as the femtosecond pump probe spectroscopy
technique, have facilitated the study of ultrafast energy transfer in the photosynthetic
systems of green plants and photodynamic therapy drugs. It has
allowed the investigation of biological and chemical processes that take place on
the ultrafast timescale and has allowed us to obtain spectral and kinetic information
on energy transfer. In addition, it has allowed time resolved experiments
in which the transient absorption of species under investigation was observed
and has elucidated molecular dynamics. In the present work this was done with
a temporal resolution of approximately 200 fs and covering a pump-to-probe
delay range of 300 fs to 2 ns.
The main aims of this study were to characterise the femtosecond pump probe
spectroscopy system, to investigate the energy transfer in the natural light
harvesting complex II (LHC II) in view of future expansion to the study of
synthesized arti cial functional light harvesting complexes and nally to study
ultrafast processes in zinc phthalocyanine (ZnPc) systems.
In photosynthetic organisms, LHC II is the most abundant light harvesting
complex and it plays an important role in light harvesting and photoprotection.
The light energy is absorbed by light harvesting complexes and transferred to
a reaction centre (RC) in an ultrafast timescale.
Phthalocyanines are a new class of photosensitiser used for photodynamic
therapy. These drugs are used to treat small and super cial tumours. The
energy transfer from the singlet excited state to the triplet excited state occurs
on an ultrafast timescale. However, recent work done on zinc phthalocyanine has
proved that the determination of the ultrafast component remains a challenge.
Several ultrafast studies carried out on ZnPc in solvents have been not only
unsuccessful to give a clear picture of the ultrafast dynamics but have also
produced divergent results.
In this study, a characterisation of the femtosecond pump probe spectroscopy
setup was done. The samples under investigation were probed by a white light
continuum. The generation of the white light continuum introduced chirp,
which in uenced the temporal evolution of the transient absorption results.
The technique used to correct the chirp introduced by white light generation
is discussed in detail. Our femtosecond pump probe spectroscopy setup was
benchmarked by using a well known dye, namely malachite green. In addition,
the investigation of the transient absorption change of LHC II, an active component
in photosynthesis, as extracted from spinach leaves and the ultrafast
dynamics of a promising photosensitiser ZnPc in dimethyl sulfoxide (DMSO) as well as in dimethyl formamide (DMF) was done. The spectral and dynamic results
obtained using these three samples are described and exponential ts to the
absorbance decay curves used to estimate the timescales of the energy transfer
processes are presented. In this experiment, the dynamics and measured time
constants related to the energy transfer between the different types of chlorophyll
in LHC II was monitored, whereas with ZnPc, the dynamics and the
measured time constants associated with solvation dynamics and vibrational
relaxation was examined. / AFRIKAANSE OPSOMMING: Die vorming van ultravinnige lig pulse en die ontwikkeling van tyd opgelosde
spektroskopiese tegnieke, soos die femtosekonde pomp proef spektroskopie tegniek,
het die studie van ultravinnige energie oordrag in fotosintetiese stelsels van
groen plante en chemiese prosesse gefasiliteer, wat kan plaasvind op die ultravinnige
tyd skaal en laat dit toe om spektrale en kinetiese informasie oor die energie
oordrag te kan bepaal. Dit het ook dit moontlik gemaak om tyd opgelosde
eksperimente te kan doen waarin ons veranderlike absorbsie van die monster kon
ondersoek en die molekulere dinamika kon ontrafel. In hierdie werk is dit gedoen
met n tyd resolusie van omtrent 200 fs termyl 'n pomp-tot-proef tydvertraging
van 300 fs tot 2 ns gebruik is.
Die hoof doelwitte van hierdie werk was om 'n femtosekonde pomp proef
spektroskopie stelsel te karakteriseer, die energie oordrag in die natuurlike ligoes
kompleks II te ondersoek met die toekomstige uitbreiding van die studie na
sintetiese lig-oes komplekse as oogmerk en laastens om ultravinnige prosesse in
Sink Ftalosianiene stelsels te ondersoek.
In fotosintetiese organismes, is lig oes kompleks II die mees volop lig oes
kompleks en speel 'n belangrike rol in lig oes en foto skerming. Die lig energie
word geabsorbeer deur lig oes komplekse en dan oorgedra na reaksie middelpunte
in 'n ultravinnige tydskaal.
Ftalosianiene is 'n nuwe klas fotosensiteerder wat gebruik word in fotodinamiese
terapie. Hierdie dwelms word gebruik om klein en oppervlakkige
gewasse te behandel. Die energie oordrag van die opgewekte singlet tot die
triplet toestand vind plaas op die ultravinnige tydskaal. Onlangse navorsingswerke
het getoon dat die bepaling van die ultravinnige komponent 'n uitdaging
bly. Verskeie vorige ondersoeke is gedoen op Sink Ftalosianiene in verskeie
oplosmiddels, en nie net het hierdie studies nie 'n helder prentjie verskaf van die
ultravinnige dinamika nie, maar het ook divergerende resultate opgelewer.
In hierdie werk word 'n karakterisering van die femtosekonde pomp proef
spektroskopie stelsel gedoen. Die monsters is ondersoek met 'n wit lig kontinuum
proef. Die vorming van die wit lig kontinuum het tjirp veroorsaak, wat
die tyd evolusie van die veranderlike absorbsie resultate beinvloed het. Die tegniek
wat gebruik was om die tjirp te korregeer word bespreek. Ons femtosekonde
pomp proef spektroskopie stelsel is gestandardiseer deur die welbekende kleurstof
malachiet groen. Ons het ook die veranderlike absorbsie van lig oes kompleks II
ondersoek, 'n aktiewe komponent in fotosintese, soos dit onttrek is uit spinasie
blare, asook die ultravinnige dinamika van die belowende photosensitizer Sink
Ftalosianiene in DMSO asook DMF. Die spektrale en dinamiese resultate verkry
vanaf hierdie drie monsters word beskryf en eksponensiele passings aan die absorbsie verval kurwes is gebruik om die tydskale van die energie oordrag prosesse
te skat. In hierdie eksperiment is dinamika en gemete tydkonstantes waargeneem
wat toegeskryf kan word aan die energie oordrag tussen verskillende
soorte chloro l in lig oes kompleks II. In die Sink Ftalosianien eksperimente is
dinamika en gemete tydkonstantes waargeneem wat toegeskryf kan word aan
solverings dinamika asook vibrasionele ontspanning.
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Photochemistry of Phenyl HalidesKarlsson, Daniel January 2008 (has links)
We have studied fundamental aspects of photo-induced dissociation kinetics and dynamics in several phenyl halides. By combining femtosecond pump-probe measurements with ab initio calculations we are able to account for several observations. In mixed phenyl halides, the dissociation kinetics is found to be dependent on the nature, the number, and the position of the substituents, and also on the excitation wavelength. A surprisingly large reduction in the dissociation time constant, compared to that of bromobenzene (~30 ps), is observed when having two or more fluorine atoms. For example, in bromopentafluorobenzene a subpicosecond time constant is obtained. This can be explained by a significant lowering of the repulsive potential energy curves (PEC) along the C-Br bond. However, several of the experimental results cannot be accounted for by one-dimensional PECs. Therefore, we suggest a refined model for the dissociation, in which the excited states of the same spin multiplicity are coupled by employing multidimensional potential energy surfaces. This model has been explicitly evaluated by quantum dynamics simulations in the case of 3-BrFPh, and it seems to be capable of capturing the main features in the measured kinetics. Thereby we are also able to clarify the role of spin-orbit coupling in these molecules.
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Stochastic Resonances and Velocity Sorting in a Dissipative Optical LatticeStaron, Alexander 04 August 2020 (has links)
No description available.
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CHARACTERIZATION OF OPTICAL LATTICES USING PUMP-PROBESPECTROSCOPY AND FLUORESCENCE IMAGINGClements, Ethan Robert 10 August 2016 (has links)
No description available.
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Structural Dynamics of DNA Hydration Shell Studied by 2D IR and Pump-Probe TechniqueLiu, Yingliang 17 November 2017 (has links)
Biochemische Prozesse treten in wässriger Umgebung auf und Wechselwirkungen der Wasserhülle mit Biomolekülen spielt eine Schlüsselrolle für deren Struktur und Funktion. In dieser Arbeit wird die Strukturdynamik der Wassermoleküle und Gegenionen in der umgebenden Wasserhülle der DNA mit der Methode der zweidimensionalen Infrarotspektroskopie (2D IR) sowie Anrege-Abfrage-Spektroskopie untersucht.
Die Ergebnisse der vorliegenden Arbeit zeigt das starke Potenzial von Schwingungsmoden an Grenzflächen für die Abbildung und das Verständnis von Wechselwirkungen zwischen Biomolekülen und ihrer Wasserhülle. In Zukunft soll dieses Konzept auch auf andere Biomoleküle angewendet werden. / Biochemical processes occur in an aqueous environment and interactions of the water shell with biomolecules play a key role for their structure and function. In this thesis, the structural dynamics of water molecules and counterions in the hydration shell of DNA is investigated by two-dimensional infrared (2D IR) spectroscopy and pump-probe transient spectroscopy. 2D IR spectroscopy is a powerful technique that can track molecular couplings between different vibrational modes and structural fluctuations of the chemical environment on a femto- to picosecond time scale. In the present study,
vibrational modes of the DNA backbone serve as probes located at the DNA-water interface.
The results of this thesis demonstrate the strong potential of interfacial vibrational modes for mapping and understanding interactions between biomolecules and their water shell. In future, this concept will be applied to other biomolecular systems.
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Ultrafast Photo-induced Reaction Dynamics of Small MoleculesKadi, Malin January 2003 (has links)
<p>The main focus of this thesis is the investigation of the dissociation dynamics of aryl halides using femtosecond pump-probe spectroscopy. In the monohalogenated aryl halides, iodo-, bromo- and chlorobenzene, the rate of dissociation following excitation at 266 nm in the gas phase increased with increasing mass of the halogen atom. This process was assigned to predissociation of the initially excited singlet (π, π*) state via a repulsive triplet (n, σ*) state due to spin-orbit interaction. In addition to the predissociative mechanism, a direct dissociation channel was observed in iodobenzene. The rate of the predissociation in bromobenzene was found to be faster in the condensed phase than in the gas phase, which can be explained by solvent-induced symmetry perturbations. <i>Ab initio</i> calculations of the potential energy surfaces of the ground state and several low lying excited states in bromobenzene have been performed in order to verify the suggested mechanism. Substituting one of the hydrogen atoms in bromobenzene affected the predissociation rate significantly. In o-, m- and p-dibromobenzene the predissociation rate increased with decreasing distance between the bromine atoms in accordance with an increased spin-orbit interaction introduced by the bromine substituent. The fastest predissociation rate was observed in 1,3,5-tribromobenzene. With chlorine and fluorine substitution, inductive and conjugative effects were found to be of importance. In the o- and m-isomers of the dihalogenated aryl halides, an additional faster dissociation channel was observed. Guided by <i>ab initio</i> calculations of the potential energy surfaces in the dibromobenzene isomers, we ascribed the fast dissociation pathway to predissociation of an initially excited triplet state. Upon methyl group substitution in bromobenzene, the decreased lifetime of the initially excited state was attributed to an incresaed density of coupled states.</p><p>Another system which has been studied in the condensed phase is diiodomethane. Using Car-Parrinello molecular dynamics simulations we observed a prompt dissociation and subsequent recombination to the isomer, iso-diiodomethane, in acetonitrile solution.</p><p>Vibrational wavepacket dynamics in the C (<sup>1</sup>Σ<sup>+</sup>) state of NaK were studied using a direct ionization probing scheme. A simple analytical expression for the pump-probe signal was developed in order to see what factors that govern direct ionization of the vibrational wavepacket. Our experimental data was consistent with a photoionization transition dipole moment that varies with internuclear distance.</p>
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Ultrafast Photo-induced Reaction Dynamics of Small MoleculesKadi, Malin January 2003 (has links)
The main focus of this thesis is the investigation of the dissociation dynamics of aryl halides using femtosecond pump-probe spectroscopy. In the monohalogenated aryl halides, iodo-, bromo- and chlorobenzene, the rate of dissociation following excitation at 266 nm in the gas phase increased with increasing mass of the halogen atom. This process was assigned to predissociation of the initially excited singlet (π, π*) state via a repulsive triplet (n, σ*) state due to spin-orbit interaction. In addition to the predissociative mechanism, a direct dissociation channel was observed in iodobenzene. The rate of the predissociation in bromobenzene was found to be faster in the condensed phase than in the gas phase, which can be explained by solvent-induced symmetry perturbations. Ab initio calculations of the potential energy surfaces of the ground state and several low lying excited states in bromobenzene have been performed in order to verify the suggested mechanism. Substituting one of the hydrogen atoms in bromobenzene affected the predissociation rate significantly. In o-, m- and p-dibromobenzene the predissociation rate increased with decreasing distance between the bromine atoms in accordance with an increased spin-orbit interaction introduced by the bromine substituent. The fastest predissociation rate was observed in 1,3,5-tribromobenzene. With chlorine and fluorine substitution, inductive and conjugative effects were found to be of importance. In the o- and m-isomers of the dihalogenated aryl halides, an additional faster dissociation channel was observed. Guided by ab initio calculations of the potential energy surfaces in the dibromobenzene isomers, we ascribed the fast dissociation pathway to predissociation of an initially excited triplet state. Upon methyl group substitution in bromobenzene, the decreased lifetime of the initially excited state was attributed to an incresaed density of coupled states. Another system which has been studied in the condensed phase is diiodomethane. Using Car-Parrinello molecular dynamics simulations we observed a prompt dissociation and subsequent recombination to the isomer, iso-diiodomethane, in acetonitrile solution. Vibrational wavepacket dynamics in the C (1Σ+) state of NaK were studied using a direct ionization probing scheme. A simple analytical expression for the pump-probe signal was developed in order to see what factors that govern direct ionization of the vibrational wavepacket. Our experimental data was consistent with a photoionization transition dipole moment that varies with internuclear distance.
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Propriétés optiques et spectroscopie non-linéaire de nanoparticules individuelles / Optical properties and non-lineaire spectroscopy of single nanoparticleBaida, Hatim 02 July 2010 (has links)
Ce travail porte sur l’étude expérimentale de la réponse optique linéaire et non-linéaire de nanoparticules métalliques individuelles. Pour cela une technique optique originale en champ lointain, basée sur la modulation spatiale de l’échantillon, a été mise en place et combinée avec une technique pompe-sonde résolue en temps à l'échelle femtoseconde. Dans un premier temps nous nous sommes intéressés à la caractérisation optique de nanoparticules modèles formées par une nanosphère d’argent encapsulée dans une couronne de silice. Nous avons mis en évidence la conséquence principale du confinement quantique électronique sur la réponse optique des nanoparticules : l'élargissement de leur résonance plasmon de surface avec la réduction de la taille (proportionnel à l’inverse du rayon, pour des nanosphères). Cette étude détaillée n’avait jamais été réalisée, car elle nécessite des mesures sur des nanoparticules uniques (pour s'affranchir des effets d’élargissement inhomogène de la résonance dus aux dispersions en taille, géométrie et environnement) et de taille connue. Ceci a été possible grâce à la mesure quantitative de leur section efficace d'extinction et/ou à la corrélation directe de l'image optique du nano-objet avec son image par microscopie électronique. La deuxième partie de ce travail a été consacrée à l'étude de la réponse optique linéaire et non-linéaire résolue en temps de nanobâtonnets d’or. Ces systèmes sont particulièrement intéressants car leurs propriétés optiques peuvent être contrôlées en modifiant leur géométrie (rapport d’aspect en particulier). Leur spectre d'extinction et sa dépendance en polarisation ont tout d'abord été étudiés au niveau de l'objet individuel. La comparaison de cette réponse optique linéaire avec des modèles théoriques a permis d'obtenir des informations sur leur orientation et géométrie. La réponse optique non-linéaire ultrarapide du même nanobâtonnet a ensuite été mesurée par une technique pompe-sonde femtoseconde à très haute sensibilité. La nanoparticule étudiée étant totalement caractérisée optiquement, une mesure quantitative de sa non-linéarité a ainsi pu être réalisée, et son origine physique déterminée à partir d'un modèle théorique. / This work focuses on the experimental study of linear and nonlinear optical responses of single metal nanoparticles. For this, an original far field optical technique, based on the spatial modulation of the sample, was set-up and combined with a femtosecond time-resolved pump-probe technique. We have first investigated the optical properties of model nanoparticles, formed by a silver nanosphere coated with a silica shell. We have highlighted the main consequence of electronic quantum confinement on the optical response of a nanoparticle: the broadening of its localized surface plasmon resonance with size reduction (proportional to the inverse of the radius, for nanospheres). This detailed study had never been realized, because it requires measurements on single nanoparticles (to eliminate the influence of inhomogeneous effects on the resonance due to size, geometry and environment dispersions) and of known size. This was possible thanks to the quantitative measurement of extinction cross-section and / or correlation of the optical image of the nano-object with its electron microscopy image. The second part of this work has been devoted to the study of the linear and time-resolved non-linear optical responses of gold nanorods. These systems are particularly interesting because their optical properties can be controlled by changing their geometry (in particular their aspect ratio). First, the extinction spectrum and its polarization dependence have been studied on individual objects. Comparison of the linear optical response with theoretical models provides information on orientation and geometry of the nanorod. The ultrafast nonlinear optical response of the nanorod was then measured with a high sensitivity femtosecond pump-probe technique. The investigated nanoparticles being fully characterized optically, a quantitative measurement of their non-linearity could be achieved, and its physical origin determined using a theoretical model.
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Spectroscopie ultrarapide de nanoparticules métalliques et hybrides / Ultrafast spectroscopy of metallic and hybrid nanoparticlesMongin, Denis 14 September 2012 (has links)
L'utilisation d'un montage expérimental pompe-sonde a permis l'étude de différentes propriétés physiques typiques de différentstypes de nano-objets. Tout d'abord, l'étude sélective d'un transfert d'électron dans un nano-hybride semi-conducteur/métal composé d'un nano-bâtonnet de CdS et d'une nanoparticule d'or en contact direct avec le semi-conducteur, a prouvé l'existence du transfert de charge entre les deux composants du nano-hybride et montré que ce phénomène intervient pour des temps caractéristiques inférieurs à 15 femtosceondes. L'étude des propriétés optiques des nanoparticules d'or ayant reçu les charges transférées a montré que l'ajout de quelques charges négatives à de petites nanoparticules d'or provoque un décalage de la résonance palsmon dans le rouge du spectre. Ensuite, la mesure des modes de vibrations fondamentaux de nano-objets métallique (spériques ou sphéroïdaux) encapsulés par une couche encapsulés par une couche diélectrique ou métallique nous a permis d'obtenir des informations sur les épaisseurs relatives des différentes couches composants les nano-objets étudiés ainsi que sur les la qualité du contact entre ces couches. Enfin, l'étude du temps typique d'interaction électron-phonon dans des nanoparticules métalliques a mis en évidence que deux méthodes de mesure optique de ce temps par spectroscopie ultrarapide sont pôssibles, et que des effets de transitions entre un comportement type "peti solide" et un comportement moléculaire sont observable pour des nanoparticules de moins de 250 atomes / The usse of a pump-probe experimental setup allowed the study of different specific physical properties of different types of nano-objects. First, the selective study of an hybrid nanoparticles comosed of a CdS nanostick and a particle directly groxwn on the semiconductor part proved the existence of a transfer between the two part of the hybrid nanoparticle and showed that this phenomenon occurs in less than 15 femtosecondes. The study of optical propertie of gold nanoparticles with an extra charge due to the transfer showed that adding few electrons to a small gold nanoparticles leads to a red shift of the plasmon resonance. Secondly, measurment of the period of fundamental vibration modes of a bilayer nano-object (spheric or elongated) composed of a metallic core and a dielectric or metallic shell lead to information on the relative thickness of the layers and the contact quality between them. LAstly, the study of the characteristic time of electron-phonon interactions in metallic nanoparticles has proven that there are two different methods of measuring this characteristic time, and its investigation for small nanoparticles (less than 250 atoms) leads to the observation of a transition form a "bulk" to a molecular behaviour
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