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1
Zheng, Junrong. "Ultrafast chemical exchange spectroscopy /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Wen, Xiaoming, and n/a. "Ultrafast spectroscopy of semiconductor nanostructures." Swinburne University of Technology, 2007. http://adt.lib.swin.edu.au./public/adt-VSWT20070426.110438.
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Semiconductor nanostructures exhibit many remarkable electronic and optical properties.
The key to designing and utilising semiconductor quantum structures is a physical understanding
of the detailed excitation, transport and energy relaxation processes. Thus the nonequilibrium
dynamics of semiconductor quantum structures have attracted extensive attention in recent years.
Ultrafast spectroscopy has proven to be a versatile and powerful tool for investigating transient
phenomena related to the relaxation and transport dynamics in semiconductors.
In this thesis, we report investigations into the electronic and optical properties of various
semiconductor quantum systems using a variety of ultrafast techniques, including up-conversion
photoluminescence, pump-probe, photon echoes and four-wave mixing. The semiconductor
quantum systems studied include ZnO/ZnMgO multiple quantum wells with oxygen ion
implantation, InGaAs/GaAs self-assembled quantum dots with different doping, InGaAs/InP
quantum wells with proton implantation, and silicon quantum dots. The spectra of these
semiconductor nanostructures range from the ultraviolet region, through the visible, to the
infrared. In the UV region we investigate excitons, biexcitons and oxygen implantation effects in
ZnO/ZnMgO multi-quantum wells using four-wave mixing, pump-probe and photoluminescence
techniques. Using time-resolved up-conversion photoluminescence, we investigate the relaxation
dynamics and state filling effect in InGaAs self-assembled quantum dots with different doping,
and the implantation effect in InGaAs/InP quantum wells. Finally, we study the optical properties
of silicon quantum dots using time-resolved photoluminescence and photon echo spectroscopy on
various time scales, ranging from microseconds to femtoseconds.
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Wen, Xiaoming. "Ultrafast spectroscopy of semiconductor nanostructures." Australasian Digital Thesis Program, 2007. http://adt.lib.swin.edu.au/public/adt-VSWT20070426.110438/index.html.
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Thesis (PhD) - Swinburne University of Technology, Centre for Atom Optics and Ultrafast Spectroscopy, 2007.Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy, Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, 2007. Typescript. Bibliography: p. 122-144.
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Foo, Edward. "Ultrafast spectroscopy of quantum dots." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393775.
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Olaizola, S. M. "Ultrafast spectroscopy of InGaN quantum wells." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414678.
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Abdel, Baki Katia. "Ultrafast spectroscopy of 2D hybrid perovskites." Thesis, Cachan, Ecole normale supérieure, 2014. http://www.theses.fr/2014DENS0052/document.
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Les pérovskites hybrides organiques-inorganiques ont attiré l'attention en raison de leurs applications potentielles dans des dispositifs optiques et plus récemment dans les dispositifs photovoltaïques. L'arrangement cristallin des pérovskites forme une structure en multi-puits quantiques dans laquelle les états excitoniques présentent une grande force d'oscillateur et une énergie de liaison importante, ce qui rend la réalisation de microcavités dans le régime de couplage fort possible à la température ambiante. Etant un matériau relativement nouveau, les pérovskites ont encore beaucoup de comportements qui ne sont pas bien compris et beaucoup de travail de recherche est nécessaire. Ce manuscrit est divisé en deux parties. Dans la première partie, la dynamique des excitons sur une pérovskite particulière (C6H5-C2H4-NH3)2PbI4 (PEPI) est étudiée à température ambiante par mesure de type pompe-sonde sous faible et fort régime d'excitation. Sous forte densité d'excitation, un processus de recombinaison Auger des excitons est présent. Une relaxation intrabande ultra-rapide a été observée. La deuxième partie du manuscrit est consacrée à l'étude de la microphotoluminescence à temperature ambiante de microcavités à base de PEPI à haut facteur de qualité. Des nouvelles pérovskites avec des propriétés optimisées (propriétés optiques d'émission, rugosité de surface et photostabilité) ont également été synthétiséesThe reason for choosing this thesis comes from the fact that in the near future,I would like to gain more knowledge and experience in scientific research and especially in the study of non linear effects in optical microcavities where new opportunities are opened and high efficient light sources could be exploited.In last ten years, an increasing number of studies are dedicated on hybrid organic-inorganic materials, due to the possibility of combining the properties both of inorganic(high mobility, electrical pumping, band engineering ) and of organic materials (low cost technology, high luminescence quantum yield at room temperature).In this context , organic-inorganic perovskites having a chemical formula (R-NH3)2MX4 where M is a metal, X halogen and R an organic chains presents a natural hybrid system . When deposited by spin coating, the molecules self-organize to form a multiple quantum wells structure. Because of the strong binding energy, optical features can be seen at room temperature. Moreover, such pervoskite presents great flexibility in their optical properties such that the spectral position of the excitonic transitions can be tailored by substituting different halides X, and the photoluminescence efficiency can be tailored by changing the organic part R. This kind of perovskites has been studied both for fundamental studies and for applications in optoelectronics. In order to increase the coupling between light and matter (exciton), perovskite has been inserted in planar microcavity and strong coupling regime has been achieved at room temperature. The strong coupling of light with exciton give rise to polariton quasi-particles, which have new properties not seen in either photons or excitons. In order to go further and have better study in stimulated scattering of polaritons in these microcavities ,a better understanding of the electronic structure as well as the excitonic interactions in these quantum wells are necessary due to the lack of information on the dynamic and on the carrier interaction of these structures. In order to study the hybrid polaritons, it will be first necessary to improve the knowledge about the relaxation in the perovskite layers. So, ultrafast pump-probe experiments will be performed on hybrid microcavities, and also on perovskite layers
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Langhojer, Florian. "New techniques in liquid-phase ultrafast spectroscopy." Doctoral thesis, kostenfrei, 2009. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/3933/.
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De, Paula Ana Maria. "Optical spectroscopy of ultrafast processes in semiconductors." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293697.
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Yuen-Zhou, Joel. "A Quantum Information Approach to Ultrafast Spectroscopy." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10317.
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In the first part of the dissertation, we develop a theoretical approach to analyze nonlinear spectroscopy experiments based on the formalism of quantum state (QST) and process tomography (QPT). In it, a quantum system is regarded as a black box which can be systematically tested in its performance, very much like an electric circuit is tested by sending a series of inputs and measuring the corresponding outputs, but in the quantum sense. We show how to collect a series of pump-probe or photon-echo experiments, and by varying polarizations and frequency components of the perturbations, reconstruct the quantum state (density matrix) of the probed system for a set of different initial conditions, hence simultaneously achieving QST and QPT. Furthermore, we establish the conditions under which a set of two-dimensional optical spectra also yield the desired results. Simulations of noisy experiments with inhomogeneous broadening show the feasibility of the protocol. A spin-off of this work is our suggestion of a witness that distinguishes between spectroscopic time-oscillations corresponding to vibronic only coherences against their electronic counterparts. We conclude by noting that the QST/QPT approach to nonlinear spectroscopy sheds light on the amount of quantum information contained in the output of an experiment, and hence, is a convenient theoretical and experimental paradigm even when the goal is not to perform a full QPT. In the second part of the thesis, we discuss a methodology to study the electronic dynamics of complex molecular systems, such as photosynthetic units, in the framework of time-dependent density functional theory (TD-DFT). By treating the electronic degrees of freedom as the system and the nuclear ones as the bath, we develop an open quantum systems (OQS) approach to TD-DFT. We formally extend the theoretical backbone of TD-DFT to OQS, and suggest a Markovian bath functional which can be readily included in electronic structure codes.
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IJAZ, PALVASHA. "Ultrafast laser spectroscopy of novel fluorescent nanocrystals." Doctoral thesis, Università degli studi di Genova, 2020. http://hdl.handle.net/11567/1001620.
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Optical properties of colloidal semiconductor nanocrystals (NCs) have been widely investigated using optical spectroscopy techniques since their birth. In particular, low-temperature spectroscopy minimizes the additional complexity induced by thermal effects, and therefore has been extensively used to investigate the temperature dependent excitonic behavior of various semiconductor materials. It has been well established that the composition, structure and the nature of the NCs surface strongly influence their optical properties. Present PhD dissertation focuses on two main generations of semiconductor colloidal NCs, i.e. 2D metal chalcogenide nanoplatelets (NPLs) and lead halide perovskite NCs. The former generation of material demonstrate remarkable optoelectronic properties, with a narrow and homogeneously broadened emission linewidth (at room temperature), fast exciton recombination and high fluorescence quantum efficiency. These advantageous properties can be further tuned in heterostructures by coating them with another semiconductor materials for instance CdSe/CdS/CdTe core/crown/barrier NPLs. Due to the staggered band offset between CdSe and CdTe, we observed emission from an indirect transition around 650 nm. As CdS forms a barrier for hole relaxation between crown and core regions, the CdSe/CdS/CdTe yielded an additional emission peak from the CdSe core, in contrast with CdSe/CdTe core/crown nanoplatelets without a barrier. The resulting dual emission was investigated as a function of temperature. The different nature of both emission peaks (direct in CdSe vs. indirect across the CdSe/CdTe interface) yielded a spectrally and temporally stable indirect transition as a function of temperature, while the emission rate of the CdSe emission increased at lower temperatures, and the spectral position shifted to shorter wavelengths. The second generation of material studied here i.e “lead halide perovskite” NCs is one of the most investigated semiconductor material in the last decade due to their ease of preparation, broadly tunable band gap, near unity fluorescence quantum efficiency and excellent color purity. We carried out a comprehensive study of size, composition and surface functionalization dependent optical properties of lead halide perovskite NCs. Contrary to most of the previous findings, we observe a single, narrow emission peak at low temperature for NCs with various sizes, compositions and surface coatings. Temperature-dependent photoluminescence (PL) and PL-lifetime data for different compositions (APbBr3, A=Cs, MA, FA) reveal that MA-based NCs were the most sensitive to temperature variations with least preservation of PL, featuring the highest thermal broadening of PL and longest lifetimes, whereas FA based NCs were the most resilient. Furthermore, a comparison of the photophysical properties of NCs having different surface coatings shows that their optical properties are strongly influenced by surface chemistry, with quaternary bromide capped NCs being the most stable samples at elevated temperature, as they retained the highest PL intensity. Considering all these results together, we provide unequivocal evidence that lead halide perovskite NCs exhibit no inhomogeneity in their PL and additionally their optical properties are strongly surface functionalization dependent. These fundamental insight into the optical properties of both generation of materials would be key for the development of future photonic devices.
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Dong, Xu. "Ultrafast infrared spectroscopy applied to spin crossover materials." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S111/document.
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Ces dix dernières années ont vu émerger des avancées technologiques majeures, nous permettant capturer une image instantanée des processus physique. L'amélioration systématique de la résolution temporelle de ces instants, grâce aux lasers (de différente sorte) aux impulsions ultracourtes, a joué un rôle important dans l'exploration des transitions de phases photo-induites dans différents matériaux, et leur potentiel applicatif. Néanmoins, ce progrès technologique incontestable a poussé à ses limites notre capacité de décrire les phénomènes hors-équilibre très complexes qui pilotent les transitions. Ils sont intrinsèquement multi-échelles dans le temps et dans l'espace, s'étalant de la femtoseconde aux plusieurs jours, et de la dimension atomique jusqu'à celle d'un cristal macroscopique. Les expériences résolues en temps permettent de séparer temporellement différents dégrées de liberté et les phénomènes pilotés par ceux-ci, au lieu d'observer seulement leur moyenne statistique. La première étape (processus photo-induit) de cette séquence temporelle est liée à l'absorption d'un photon, la deuxième (élastique) est pilotée par la dilation du volume macroscopique du matériau, et la troisième étape (thermique) est due aux effets de chaleur. Cette approche séquentielle offre de nouvelles possibilités pour mieux comprendre comment impacter les matériaux de façon contrôlée et efficace. Les lasers opérant dans le moyen infrarouge (mid IR) permettent de suivre le déroulement d'une transition de phase par le changement de vibrations des molécules/liaisons ciblées. Cette spécificité au site moléculaire combinée avec la résolution en temps ultracourte devrait ouvrir une nouvelle fenêtre d'observation des phénomènes qui échappaient aux études scientifique. Ce travail de thèse a commencé exactement dans cet esprit. L'effort majeur a été dédié à l'application de la spectroscopie mid IR ultrarapide aux matériaux présentant une conversion de l'état de spin, [Fe(3-MeO-SalEen)]2PF6 en particulier. La principale difficulté de ce travail consistait à décrypter le contenu spectral des molécules hors-équilibre. Nous avons découvert que l'approche utilisé dans les spectroscopies résolues en temps de plus haute énergie (UV/VIS) ne suffit pas pour étudier la problématique posé dans le cadre de cette thèse. Une nouvelle approche a été pensée pour modéliser les spectres résolus en temps, et celle-ci consistait à séparer la réponse spectrale en deux contributions : le transfert de poids spectral, et un décalage spectral. J'ai pu démontrer que ces deux contributions suivent sensiblement le changement d'état de spin, et la pression (dilatation du volume). L'analyse de données basée sur ce modèle, corrobore les résultats obtenus jusqu'alors avec d'autres techniques. Sur l'échelle de temps ultracourts, plus difficile à modéliser, nous avons pu néanmoins résoudre très clairement le refroidissement vibrationnelle (VC) de l'état électronique haut spin -chaud. A ma connaissance, ce phénomène dans un système solide présentant crossover de spin n'a jamais été observé directementThe past few decades have seen great advancements in technology that allow us to capture the picture of a physical process, as the adage “seeing is believing” implies how people understand the world. The increasing temporal resolution of lasers played an important role in the study of materials, among which materials exhibiting photo-induced phase transition are of great importance thanks to their potential for future applications. However, as we proceed further and further in the investigation of the mechanism of phase transition, we found ourselves confronted with the very complex nature of phase transition dynamics. It is intrinsically multi-scale in time and space, from femtosecond to days and from atomic dimensions to macroscopic distances. Time resolved experiments disentangle different degrees of freedom and different phenomena in a step-like manner, rather than providing a statistical average. The first step is photo induced due to absorption of photons, the second step (elastic step) is pressure induced due to volume dilation, and the third step is temperature induced due to dissipation of heat. This step-like approach offers an opportunity to understand the mechanism, so that we could effectively impact the materials and possibly control phase transition. Mid IR lasers have a unique advantage of monitoring phase transition through vibrational modes on specific molecular sites. Implementing ultrafast mid IR spectroscopy in phase transition materials should be therefore very insightful in discovering new phenomena and revealing hidden mechanism. This PhD project, focusing on mid IR technique, started exactly in this context. The main effort is dedicated to the application of ultrafast mid IR spectroscopy to the spin crossover solids, [Fe(3-MeO-SalEen)]2PF6. The major challenge in this work was to comprehend the shape of transient mid IR spectra. We found out that this is conceptually different from the experiences accumulated in UV/VIS spectroscopy. A suitable model had to be developed, separating the transient IR spectra into two contributions: spectral weight transfer and spectral shift. I demonstrated that these two components are sensitive to the spin change and pressure effect (volume dilation), respectively. Data analysis based on the new model shows consistency with previously published results. On the ultrafast timescale, more difficult to fit our model to, vibrational cooling (VC) of electronically hot HS state has been very well resolved. To the best of my knowledge, direct observation of VC in solid state SCO compound by IR spectroscopy has not been reported earlier
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Polshakov, Dmitrii Arkadyevich. "Ultrafast spectroscopy and dynamics of nitrenes and carbenes." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1130968887.
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Johansson, Pia. "Ultrafast Spectroscopy of Atomic and Molecular Quantum Dynamics." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-1252.
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Hope, Michael John. "Spectroelectrochemistry and Ultrafast Polarisation Spectroscopy of Buckminsterfullerene Anions." Thesis, University of East Anglia, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490585.
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A spectroelectrochemical cell for the synthesis and in situ spectroscopic analysis of oxygen-reactive Buckminsterfullerene anions was designed and constructed. This cell enabled the first two anions of Buckminsterfullerene to be prepared and stabilised for steady state and ultrafast spectroscopy. A third anion was obtainable and was similiarly prepared although it was less stable. Each of these anions has a characteristic absorption spectrum with features towards the red of the visible spectrum and into the near-infrared. In order to observe these spectra it was necessary to obtain and calibrate a spectrometer with a response in the 800 to 1100 nm region. Spectra were separated for each anion, given assignments and correlated with electrochemical measurements. Spectroelectrochemical studies on the monoanion lead to a new assignment of its vibronic structure arising from a dynamic Jahn-Teller effect. A fluorescence spectrum of the trianion was recorded for the first time, and fluorescence data for the monoanion were observed with higher resolution than has been previously reported. Analysis of the monoanion fluorescence data and solvent effects has revealed further structure which suggests that the vibronic coupling is more complex than initially thought. Laser spectroscopy using a home built ultrafast cavity dumped nearinfrared laser probed the population and orientati~nal relaxation ofthe mono and dianions. Our aim was to investigate possible pseudorotation in the monoanion, arising from a dynamic Jahn-Teller effect. Preliminary data measured suggest a reorientation between 2 and 5 ps. This relaxation' is faster than expected for molecular rotations, suggesting that we might be observing pseudorotation. This warrants further investigation by temperature and viscosity dependent studies.
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Klieber, Christoph. "Ultrafast photo-acoustic spectroscopy of super-cooled liquids." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57801.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.Vita. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 219-231).
Picosecond laser ultrasonic techniques for acoustic wave generation and detection were adapted to probe longitudinal and transverse acoustic waves in liquids at gigahertz frequencies. The experimental effort was designed for the study of supercooled liquids whose slower relaxation dynamics extend to gigahertz frequencies at high temperatures and whose faster dynamics are centered uniquely in the gigahertz frequency range. The experimental approach used a unique laser pulse shaping technique and, in the case of shear acoustic waves, a crystallographically canted metal transducer layer, to generate frequency tunable compressional and shear acoustic waves. Either time-domain coherent Brillouin scattering or interferometry was used to detect the waves in or after propagation through a liquid layer. The study of liquid-state gigahertz acoustic behavior required advances in both the experimental methodology and in the theoretical modeling of the results. A particular challenge was posed by the extraordinarily strong damping of gigahertz-frequency acoustic waves in liquids at some temperature ranges. This demanded the design and construction of a liquid sample cell allowing access to a wide range of liquid thicknesses, from less than a nanometer up to several microns. This was achieved by squeezing the liquid between two specially prepared high quality optical substrates held in a non-parallel configuration by a custom-designed sample holder jig. Several metallic layer materials were used for conversion of optical pulse energy into acoustic waves that were launched into the liquid samples, and different probe geometries were developed to enable access to a wide frequency range. The developed spectroscopic strategies were then applied to the study of two liquids, glycerol and tetramethyl tetraphenyl trisiloxane (DC704). Measurements of the density responses of both liquids from 400 K to below their respective glass transition temperatures were carried out. Longitudinal acoustic waves were either monitored via time-domain Brillouin scattering in the liquid or via interferometry after transmission through variably thick liquid layers, granting access to longitudinal acoustic frequencies from 10 GHz up to about 200 GHz. The information obtained on gigahertz frequency liquid relaxation was pieced together with data from several other techniques to create broadband relaxation spectra (from millihertz up to gigahertz), allowing characterization of the complex structural relaxation dynamics over many orders of magnitude and enabling both empirical modeling and testing of the predictions of the mode-coupling theory of supercooled liquids. The requirements for gigahertz shear wave generation and detection, including the properties of the photo-acoustic transducer materials, the sample and experimental geometry, and the detection material choices, are discussed. Results on shear wave propagation in glycerol and DC704 are presented. The technique for shear wave generation and detection is not limited to the study of viscous liquids but can also be applied to liquids like water, from which initial results are presented.
by Christoph Klieber.
Ph.D.
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Mahat, Meg Bahadur. "Ultrafast Spectroscopy of Hybrid Ingan/gan Quantum Wells." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc149635/.
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Group III nitrides are efficient light emitters. The modification of internal optoelectronic properties of these materials due to strain, external or internal electric field are an area of interest. Insertion of metal nanoparticles (MNPs) (Ag, Au etc) inside the V-shaped inverted hexagonal pits (IHP) of InGaN/GaN quantum wells (QWs) offers the potential of improving the light emission efficiencies. We have observed redshift and blueshift due to the Au MNPs and Ag MNPs respectively. This shift could be due to the electric field created by the MNPs through electrostatic image charge. We have studied the ultrafast carrier dynamics of carriers in hybrid InGaN/GaN QWs. The change in quantum confinement stark effect due to MNPs plays an important role for slow and fast carrier dynamics. We have also observed the image charge effect on the ultrafast differential transmission measurement due to the MNPs. We have studied the non-linear absorption spectroscopy of these materials. The QWs behave as a discharging of a nanocapacitor for the screening of the piezoelectric field due to the photo-excited carriers. We have separated out screening and excitonic bleaching components from the main differential absorption spectra of InGaN/GaN QWs.
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Polshakov, Dmitrii A. "Ultrafast spectroscopy and dynamics of nitrenes and carbenes." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1130968887.
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Bizimana, Laurie A. "Investigating Nonadiabatic Dynamics in Phytochromes with Ultrafast Spectroscopy." Thesis, New York University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10751008.
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Improving our understanding of nonadiabatic processes is essential for informed development of photoelectric technologies. Nonadiabatic dynamics arise due to nuclear motion on coupled potential energy surfaces. These nonadiabatic couplings are high in the regions of avoided crossings, where potential energy surfaces approach each other, and near infinity at conical intersections, where two potential energy surfaces are degenerate. Regions of high nonadiabatic coupling play an important role in the electronic dynamics of a system because of their ability to create very rapid (on the order of tens of femtoseconds) radiationless transitions between potential energy surfaces. Recent computational work has shown conical intersections to be prevalent in photochemical reactions; however, there are very few experimental investigations of conical intersections in condensed phase reactions. This is due to the extreme difficulty of detecting their subtle signatures experimentally. In biophysical chemistry, the only system that has been investigated is rhodopsin. In this photoisomerization reaction, the conical intersection produces a very rapid photoproduct formation with a quantum yield of approximately 85%. This led to the idea that the mere presence of a conical intersection in a biophysical system results in photoproducts formed with high quantum yields. In contrast, computational work shows conical intersections to be ubiquitous in all types of photoisomerization reactions. In this thesis I provide experimental evidence of conical intersections in a system with a quantum yield of <15%, thereby showing that the topography of the conical intersection has an effect on the quantum yield of the photoisomerization, and does not just by its mere presence result in a high quantum yield.
The system we investigate here is phytochrome Cph1Δ. It is an ideal model system because it is reversibly photoisomerizable and has known single--site mutations that result in altered potential energy surfaces. However, this system is experimentally very challenging to investigate. Conical intersections already have very subtle signatures, and low quantum yield, combined with the potential for overlapping signals due to the forward and reverse reactions, make detecting these signals even more difficult. In this thesis, I first describe our design and construction of a two--dimensional electronic spectroscopy (2D ES) and visible femtosecond transient transmittance spectrometer capable of performing these measurements. We perform a set of experiments on cresyl violet perchlorate, a laser dye, to show the importance of using our balanced detection methods and correct signal averaging schemes to maximize signal--to--noise and to ensure the signals converge to the correct value. We then use our spectrometer to probe for the presence of nonadiabatic dynamics in both the forward and reverse photoisomerization reactions of Cph1Δ. First, we use high sensitivity 2D ES and vibrational coherence spectroscopy to resolve a long--standing controversy about whether the forward reaction proceeds adiabatically. We find no evidence of nonadiabatic dynamics, and our results are consistent with a single ground state population undergoing a purely excited--state photoisomerizaion process. In the reverse reaction we identify and characterize a conical intersection using transient transmittance spectroscopy and 2D and 3D ES. This result expands on the notion that the presence of a conical intersection results in ultrafast dynamics and high photochemical quantum yield, showing that the topography of the conical intersection plays a role in determining the outcome of a photoexcitation. We also perform the same experiments on two single--site phytochrome mutants as control measurements. Finally, I present the theory of nonadiabatic coupling, and through simulations and experiments demonstrate the ability of our methods to identify signatures of non--Condon activity.
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Huang, Hailong. "Ultrafast laser spectroscopy of half -metallic chromium dioxide." W&M ScholarWorks, 2006. https://scholarworks.wm.edu/etd/1539623491.
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This thesis presents ultrafast laser pump-probe differential transmission experiments on epitaxial CrO2 (110). The experiments were conducted at the wavelengths of 600 nm, 800 nm and 1200 nm, corresponding to the transition energies of 2 eV, 1.5 eV and 1 eV respectively. The wavelength dependent results, comparing with linear optical absorption, revealed the electronic structure of the material. The experimental results also showed polarization dependence of the probe beams. This is attributed to the electronic orbital anisotropy.;Temperature dependence was observed in the pump-probe experiments. The ultrafast transmission data show similar temperature dependence as ultrafast MOKE (Magneto-Optical Kerr Effect) data. A critical change of transient transmission was observed at the Curie temperature of 386 K. Spin decay processes are discussed based on these temperature dependent time resolved data.;Ultrafast MOKE experiments are also presented. Oscillations of the time resolved MOKE signal corresponding to the ferromagnetic resonance were observed. The magnetic anisotropies of the CrO2 thin film were studied by analyzing these oscillations. A computer program was developed for data analysis.;A general discussion of the relation between magnetic properties and the electronic properties of the material is delivered.
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ARESTI, MAURO. "Ultrafast Optical Spectroscopy Techniques applied to colloidal nanocrystals." Doctoral thesis, Università degli Studi di Cagliari, 2014. http://hdl.handle.net/11584/266450.
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In this thesis I will describe my experimental work based on ultrafast optical spectroscopy techniques applied to colloidal nanocrystals.
Colloidal semiconductor nanocrystals in recent years have attracted a lot of attention in particular in optoelectronic applications, because they present
unique optical, electronic and charge carrier transport properties that can be easily modified via colloidal chemical synthesis.
In the first chapter of this thesis, I will introduce the basic concepts of nanocrystals and their optical properties, I will consider some simple models
to explain the physical properties of semiconductor nanocrystals. I will briefly describe the colloidal chemical synthesis of these nanocrystals and how we
can change the optical properties by simply acting on the colloidal chemical synthesis.
In the second chapter I will describe the basic concepts of ultra fast optical spectroscopy techniques used in my experimental work. I will describe the basic principles and the experimental set-up of the two main techniques that I
used: time-resolved photoluminescence spectroscopy (TR-PL) and transient absorption spectroscopy or also called Pump Probe. These two techniques allow to investigate in a very precise way the main optical properties and dynamics of charge carriers in nanocrystals.
In the third chapter I will describe my experimental work based on timeresolved photoluminescence spectroscopy applied to CdSe=CdS core=shell nanocrystals. These nanocrystals are a reference nanocrystals and their optical
properties are extensively investigated, however, some aspects are not fully understood, for example, the instability or blinking of the light emission
under constant illumination in these nanocrystals is still an unsolved problem that limits the real applications. The particular spectroscopic technique that I have used variable pulse rate photoluminescence spectroscopy revealed
the causes of this issue, and will give us a solution to resolve it.
In the fourth chapter I will discuss novel nanostructures of CdSe=CdS multi branched shape, in this case octapod shaped nanocrystals consist of eight arms made of CdS grown on a CdSe core, these present a large crosssection for light absorption and efficient charge separation ideally suited for applications of photocatalysis. The optical spectroscopy technique used to investigate the properties of these nanocrystals are the transient absorption
spectroscopy.
In the fifth chapter I will discuss experimental work on Bi2S3 semiconductor nanocrystals and I will describe related optical techniques used to study the optical and electronic properties. This nanocrystal has excellent
properties of optical absorption of solar radiation and can be used for the realization of solar cells. Another important property of Bi2S3 is its nontoxicity
that will allow in the future to achieve efficient solar cells and easy disposal and simultaneously not damaging to the environment.
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Mörz, Florian [Verfasser]. "Ultrafast laser sources : tunable, ultrafast laser sources for near- and mid-IR spectroscopy / Florian Mörz." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2020. http://d-nb.info/1222515504/34.
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Rohrdanz, Mary A. "Intermolecular communication via lattice phonons, probed by ultrafast spectroscopy /." view abstract or download file of text, 2005. http://wwwlib.umi.com/cr/uoregon/fullcit?p3190543.
Full textAbstract:
Thesis (Ph. D.)--University of Oregon, 2005.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 79-80). Also available for download via the World Wide Web; free to University of Oregon users.
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Zhang, Chi, and 张驰. "Ultrafast temporal spectroscopy based on parametric mixing time-lens." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/200358.
Full textAbstract:
With the increased requirement on the ultrafast measurement technology, how to resolve the spectral dynamics has the top priority on the research list, since spectrum is an essential carrier for most of the physical or chemical phenomena. According to the Nyquist-Shannon sampling theorem, if a function 𝑥(𝑡) contains no frequencies higher than 𝐵 Hz, it is completely determined by giving its ordinates at a series of points spaced 1/(2𝐵) seconds apart. Since most of the conventional optical spectrum analyzers (OSAs) are operated with the sampling rate (or frame rate) of 5 Hz, it results in the resolvable bandwidth of the spectrum dynamic is less than 2.5 Hz. With the development of the space-time duality, the analogy transforms the conventional spatial dimension into the time axis, and the well-known spatial models inspire us in performing their counterparts in the time domain. As one of the most powerful tools in achieving ultrafast time axis information, time-lens plays a more and more important role in the single-pixel imaging system.
By fully analyzing the diploma of the previous optical spectrum resolving mechanisms, in this thesis, for the first time, we raised up the concept the parametric spectrotemporal analyzer (PASTA), which is based on the time-lens focusing mechanism. Here the spectrum resolving frame rate is increased to 100 MHz, then the observable spectrum dynamic bandwidth could be 50 MHz, which is sufficient for most of the ultrafast phenomena. In the PASTA system, the time-lenses are implemented with the fiber optical parametric amplifier (FOPA) based parametric mixer, which provides higher conversion efficiency and repetition rate. On the other hand, the dispersion based dispersive Fourier transformation (DFT) technology generates the swept-pump for the FOPA, as well as the temporal dispersion medium.
This research in this thesis is a fundamental study on the newly PASTA system, from its origin and the theoretical background, to the implementation techniques and operation performances. From its implementation, its principles are strongly related with the combination of the dispersion and the Kerr nonlinear effects, especially the swept-pump FOPA in the time-lens part. The DFT technique, in generating the fast swept-source, has also find its applications in the ultrafast serial time-encoded amplified microscopy (STEAM) and swept-source optical coherence tomography (SS-OCT) systems.
Finally, the single-lens PASTA prototype is capable of resolving 5-nm wavelength range with 0.03-nm resolution under 100-MHz frame rate. Moreover, besides the singlelens PASTA, the telescope/wide-angle configurations have also been investigated experimentally to achieve the spectrum zoom in/out ratio as high as 17 times, here we have obtained the sharpest resolution of 5 pm (<1 GHz) with the telescope configuration, and the widest observation range of 9 nm with the wide-angle configuration.
My research efforts presented in this thesis mainly leverage the ultrafast characteristics of the time-lens system, from theory to implementation, and achieve the real-time optical spectrum analysis – the PASTA system. PASTA is not only essential in observing some non-repetitive ultrafast phenomena, but also provides a potential solution for the frequency to time transformation in some ultrafast bio-medical imaging systems.published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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Roland, Thomas. "Ultrafast spectroscopy of new organic molecules for photovoltaic applications." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE009/document.
Full textAbstract:
Cette thèse porte sur l'étude de nouvelles molécules organiques par différentes méthodes de spectroscopie. La combinaison de techniques de fluorescence résolue en temps, d'absorption différentielle résolue en temps et de spectro-électro-chimie avec des méthodes d'analyse globale permet de déterminer la photo-dynamique des molécules étudiées.Deux familles de molécules ont été étudiées. La première est une antenne de type donneur basée sur le pigment BODIPY. La seconde consiste en une triade donneur-accepteur-donneur (DAD) ayant des propriétés d'auto-organisation. Après une première génération de mol écules dont on a montré les limitations (temps de vie de l'état transfert de charge très court, d'environ 55 ps), une seconde génération de mol écules a été développée, incluant de nombreuses variations du groupe donneur, ce qui a permis de déterminer l'impact des-dites variations. Entre autres, un temps de vie de l'état transfert de charge de plus d'une nanoseconde est observéThe topic of this thesis is the study -through different spectroscopy methods- of new organic molecules for photovoltaic applications. Combination of time resolved fuorescence, time resolved differential absorption and spectro-electro-chemistry with global analysis methods allowed to determine the photo-dynamics of the studied molecules. Two familiesof molecules have been studied. The first one is a donor-type antenna based on the BODIPY dye. The second consists in a donor-acceptor-donor (DAD) triad, with self-organizing properties. After a first generation of molecules that we proved to be limited by a short life time of its charge transfer state (about 55 ps), a second generation of molecules wasdeveloped, including several variation of the donor group, which allowed to study the impact of said variation. Among others, a charge transfer state lifetime longer than 1 nanosecond was observed
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Qiu, Weihong. "Ultrafast Protein Hydration Dynamics Investigated by Femtosecond Fluorescence Spectroscopy." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1222202233.
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Eftekharibafrooei, Ali. "Ultrafast Vibrational Spectroscopy and Dynamics of Water at Interfaces." Diss., Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/107351.
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ChemistryPh.D.
Over the past two decades, vibrational sum-frequency generation (VSFG) has been applied as a versatile technique for probing the structure and dynamics of molecules at surfaces and interfaces. The excellent surface specificity of the SFG allows for probing different kinds of liquid interfaces with no or negligible contribution from adjacent and much deeper bulk phase. VSFG spectroscopy has provided evidence that the structure of the water at interfaces is different from the bulk. With the ultrafast pulses, VSFG can also be used as a probe of ultrafast vibrational dynamics at interfaces. However, apart from a few pioneering studies, the extension of VSFG into time domain has not been explored extensively. Here VSFG is used as a probe of ultrafast vibrational dynamics of water at silica interfaces. Silica is an excellent model system for the solid phase where one can systematically vary the surface charge via bulk pH adjustment. The extension of the surface electric field, the interfacial thickness and surface accumulation of ions at a charged silica surface were studied using IR pump-VSFG probe spectroscopy. A vibrational lifetime (T1) of about 250 fs, similar to bulk H2O, was observed for the O-H stretch of H2O/silica interface when the silica surface is negatively charged. At the neutral surface, where the thickness of interfacial water is smaller than at the charged surface, the vibrational lifetime of O-H stretch becomes more than two times longer (T1~ 600 fs) due to the decreased number of neighboring water molecules, probed by SFG. The fast T1 at negatively charged surface begins to slow down by screening of the penetration of surface electric field via adding salt which suggests the primary reason for similar vibrational dynamics of water at charged interface with bulk water is the penetration of electric field. By decoupling of OH of HDO in D2O, a frequency dependent vibrational lifetime is observed with faster T1 at the red compared to the blue side of the hydrogen bond spectral region. This correlates with the redshift of the SFG spectra with increasing charged surface and is consistent with a theoretical model that relates the vibrational lifetime to the strength of the hydrogen bond network.
Temple University--Theses
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Walke, Daniel John. "New instrumentation and methods for ultrafast pump-probe spectroscopy." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48040.
Full textAbstract:
Recent advances have led to the demonstration of trains of attosecond pulses and isolated attosecond pulses in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) regions of the electromagnetic spectrum in a number of laboratories. This has raised the possibility of direct time resolved measurements of correlation driven electron dynamics within molecules, with a long term aim of unprecedented control over the dynamics of matter at atomic and molecular length scales. Particular interest has arisen towards the possibility of a charge migration mechanism within molecules, in which purely electron driven processes result in the movement of charge around an excited molecule in the absence of any nuclear dynamics. However, even once these sources have been established, using them in time resolved experiments is challenging. This is due to extremely short time-scales involved, the complexity of the processes under study, and the limitations of currently available attosecond sources. In this thesis I describe the development of novel instrumentation and methods for attosecond pump – probe experiments on electron dynamics in molecules. Strategies for the experimental study of charge migration are reviewed in detail which motivates the design and implementation of a purpose built instrument combining an electron velocity map imaging (VMI) spectrometer and an ion time of flight (iTOF) spectrometer. This instrument is designed in tandem with the development and characterisation of an isolated pulse at the new photon energy of 20eV. This 20eV pulse is intrinsically synchronized with another attosecond pulse at 90eV. Together, the new instrument and light source represent a unique capability for the investigation of electron dynamics in molecules. Finally, the first experimental results are presented and perspectives for future studies using the new developments are discussed.
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Shattuck, Jeffrey T. "Ultrafast infrared spectroscopy of biological membranes and biological water." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12847.
Full textAbstract:
Thesis (Ph.D.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Ultrafast infrared pump-probe and photon echo spectroscopy is used to provide insight into the differences ofthe hydrogen bonding network ofwater in neat liquid, aqueous solutions and lipid membrane environments. Due to water's fundamental role in biology and biological processes, it is essential to understand its interactions with these environments. The vibrational energy relaxation (VER) mechanism ofthe libration-bend combination band of neat water was investigated using pump-probe spectroscopy. Previous studies concentrate on the kinetics stretch and bend normal modes. Two concerted pathways were needed to describe the energy relaxation. In the first pathway vibrational energy leaves the excited combination band directly (140 fs) populating low frequency modes. In the second pathway the combination band decays to the bend normal mode which subsequently relaxes to librations and finally to low frequency modes (840 fs). Pump-probe spectroscopy was used to determine perturbations to the VER of nitrous oxide (N20) dissolved in water caused by ionic solutes and membranes. Altering the cation for a number ofchloride salts showed the VER rate ofN20 to follow a Hofmeister series trend. Kosmotropes Ca2+, and Mg2+, increased the lifetime of the v3 mode ofN20 while chaotropes (Cs+) decreased the lifetime. The v3 lifetime of N20 also showed that charged lipid headgroups alter the hydrogen bonding network of interlamellar water. The v3 lifetime ofN20 dissolved in oriented water near the lipid headgroups was 20 ps and changed by over a factor of two compared to its bulk value of 9 ps. Both experiments show that strongly oriented water slows the N20 VER by changing the bulk water structure of the intramolecular hydrogen bonding network. Homodyne photon echoes of N20 in water and octanol, both model environments for head and tail portions of lipids, showed the timescales of spectral diffusion for each solvent. Spectral diffusion timescales for N20 in water is caused by inertial rotational motions, 130 fs, and hydrogen bond breaking, 1.5 ps. In octanol spectral diffusion is due to inertial rotation (230 fs), hydrogen bond breaking (3.5 ps), and solvent reorientation (35 ps). Anisotropy measurements are consistent with this interpretation.
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Lagoudakis, Pavlos G. "Exciton polariton dynamics in semiconductor microcavities." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274583.
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Schiff-Kearn, Aidan. "Experimental and Numerical Investigations into Terahertz Time-Domain Spectroscopy." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38708.
Full textAbstract:
This Master's thesis presents numerical and experimental results that benchmark a state-of-the-art terahertz time-domain spectrometer. We begin by describing the theory behind the nonlinear optical mechanisms through which we generate and detect short pulses of THz radiation. Based on a coherent electro-optic detection scheme, our measurements trace out the oscillating electric field of the THz pulses generated from the optical mixing process of optical rectification. A numerical simulation based on the theory presented in this work helps present the physical intuition behind our use of these nonlinear optical processes and is furthermore used to complement our measurements with theory. Utilizing the simultaneous amplitude and phase information provided by our detection scheme, we perform terahertz time-domain spectroscopy on sample materials. Our samples of interest are the III-V zinc-blende semiconductors GaP and ZnTe which are nonlinear media popular for their advantageous dispersive and absorptive properties in the terahertz range. Therefore, the thesis culminates in the demonstration of a material parameter extraction procedure which we use to obtain the complex refractive index of a GaP crystal and a ZnTe crystal.
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Golla, Dheeraj, and Dheeraj Golla. "Ultrafast Dynamics of Two Dimensional Materials." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626303.
Full textAbstract:
Two dimensional (2D) materials are poised to revolutionize the
future of optics and electronics. The past decade saw intense research
centered around graphene. More recently, the tide has shifted to a bigger
class of two-dimensional materials including graphene but more
expansive in their capabilities. The so called ‘2D material zoo’ includes
metals, semi-metals, semiconductors, superconductors and insulators.
The possibility of mixing and matching 2D materials to fabricate
heterostructures with desirable properties is very exciting.
To make devices with superior electronic, optical and thermal
properties, we need to understand how the electrons, phonons and other
quasi particles interact with each other and exchange energy in the
femtosecond and nanosecond timescales. To measure the timescales of
energy distribution and dissipation, I used ultrafast pump-probe
spectroscopy to perform time-domain measurements of optical
absorption. This approach allows us to understand the impact of manybody
interactions on the bandstructure and carrier dynamics of 2D
materials.
After a brief introduction to femtosecond laser spectroscopy, I will
explore the transient absorption dynamics of three classes of 2D
materials: intrinsic graphene, graphene-hBN heterostructures and
Transition Metal Dichalcogenides (TMDs). We will see that using pumpprobe
measurements around the high energy M-point of intrinsicgraphene, we can extract the value of the acoustic deformation potential
which is vital in characterizing the electron-acoustic phonon
interactions. In the next part of the thesis, I will delineate the role of the
substrate in the cooling dynamics in graphene devices. We will see that
excited carriers in graphene on hBN substrates cool much faster that on
SiO2 substrates due to faster decay of the optical phonons in graphenehBN
heterostructures. These results show that graphene-hBN
heterostructures can solve the hot phonon bottleneck that plagues
graphene devices at high power densities. In the last part, I will
demonstrate the role of phonon induced bandgap renormalization in the
carrier dynamics of TMD materials and measure the timescale of
phonon decay through the generation of low-energy phonons and
transfer to the substrate. This study will help us understand carrier
recombination in TMD devices under high-bias conditions which show
great potential in opto-electronic applications such as photovoltaics,
LEDs etc.
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Poulin, Peter Roland 1973. "Coherent lattice and molecular dynamics in ultrafast single-shot spectroscopy." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32430.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Includes bibliographical references.
This thesis focuses on the development, refinement, and application of dual- echelon single-shot ultrafast spectroscopy to the study of coherent nuclear motion in condensed phase systems. The general principles of the single-shot method are described, and particular emphasis is given to the general applicability and shortcomings of this technique and the extraction of data from raw laboratory images. Coupled to the single-shot system is a synchronously pumped dual-beam noncollinear optical parametric amplifier which was developed to provide independently tunable pump and probe beams in the visible and UV regions of the electromagnetic spectrum. The second part of the thesis concerns the application of this technique to the study of atomic motions in liquids and solids. Single-shot nonresonant impulsive stimulated Raman scattering (ISRS) measurements in m-iodoanisole and bismuth germanate reveal the existence of transient coherent behavior. High-field resonant excitation of the semimetals bismuth, antimony and tellurium, as well as the semiconductor germanium telluride, reveals dramatic lattice anharmoniticity as a function of pump fluence. Finally, ultrafast photodissociation of the triiodide ion both in solution and in the solid state gives considerable insight regarding the role of the local environment in mediating chemical reaction dynamics.
by Peter Roland Poulin.
Ph.D.
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Russell, David Morrison. "Electronic transfer processes in semiconductor polymers probed by ultrafast spectroscopy." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620681.
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Knighton, Brittany E. "Nonlinear Ultrafast Excitation and Two-Dimensional Terahertz Spectroscopy of Solids." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9190.
Full textAbstract:
Ultrafast spectroscopy allows us to probe and understand material properties. With it, we can measure phonon-polaritons (optical phonons coupled with light) and the resulting dispersion curve in lithium niobate. Customizing the excitation source in ultrafast measurements can excite phonon modes to large amplitudes, allowing the experimental exploration of the Potential Energy Surface in solids. However, stronger pump fluences and bigger signal isn't always the answer in ultrafast spectroscopy. When sample signals and their nonlinear and mechanisms cannot be distinguished with 1D measurements, simple 2D THz measurements are a great place to start searching for distinct factors as was the case in cadmium tungstate. 2D measurements when paired with modeling and first principles calculations can reveal cutting edge information about exciting materials.
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Doig, Katie I. "Ultrafast and continuous-wave spectroscopy of multiferroic oxide thin films." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:e44e0a2a-a675-4923-90de-a1bdfa24f184.
Full textAbstract:
Thin film multiferroic oxides with co-existing ferroelectric and ferromagnetic ordering have attracted much interest in recent years, partly as a result of the enhancements achieved through the adoption of strained thin film geometries. This thesis presents work on two such thin film oxides; lanthanide substituted BiFeO3 and Fe substituted PbTiO3. Coherent magnons and acoustic phonons were impulsively excited and probed in thin films of the room temperature multiferroic Bi1-x-yDyxLayFeO3 using femtosecond laser pulses. The elastic moduli of rhombohedral, tetragonal and rare-earth doped BiFeO3 were determined from acoustic mode frequencies in conjunction with spectroscopic ellipsometry. A weak ferromagnetic order, induced alternately by magnetization in the growth direction or by tetragonality, created a magnon oscillation at 75 GHz, indicative of a Dzyaloshinskii-Moriya interaction energy of 0.31 meV. Bulk crystals and thin films of PbTi1-xFexO3 (PTFO) are multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pbn+1(Ti1-xFex)nO3n+1 forms spontaneously during pulsed laser deposition of PTFO on LaAlO3 substrates. High-resolution transmission electron microscopy, x-ray difraction and x-ray photoemission spectroscopy were utilised to perform a structural and ompositional analysis, demonstrating that n≃8 and x≃0.33. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes, and the observation of second harmonic generation, establishes a non-centrosymmetric point group for Pbn+1(Ti0.67Fe0.33)nO3n+1-δ consistent with ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.
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Cheng, Yu-Hsiang. "Photoinduced dynamics studied by ultrafast single-shot pump-probe spectroscopy." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122684.
Full textAbstract:
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 155-168).
This thesis focuses on the development of dual-echelon single-shot spectroscopy and its applications to study irreversible photoinduced dynamics. First, the ultrafast laser sources and the related control and characterization techniques are discussed. In particular, we have invented a two-stage dual-beam noncollinear optical parametric amplifier to provide tunable sources for pump-probe spectroscopy. Next, the experimental setup of dual-echelon single-shot spectroscopy is illustrated with great detail and possible noise sources and correction methods are explored. Using the single- shot technique, we studied photoinduced dynamics in three different materials. In bismuth, we found a transition into a transient symmetric phase at high fluences. We showed the coherent control of phonon parameters with pump-pump-probe experiments. We also simulated the carrier and phonon dynamics using a modified two-temperature model. In tellurium, we demonstrated that the amorphization of crystalline tellurium induced by femtosecond pulses is a thermal process. We also estimated the lattice temperature by the change in phonon frequency. In a strained manganite film, we observed a photoinduced persistent insulator-to-metal transition and showed the partial recovery of the generated metallic phase to the insulating phase.
by Yu-Hsiang Cheng.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Parkinson, Patrick. "Ultrafast electronic processes at nanoscale organic-inorganic semiconductor interfaces." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:e68168c6-bcc0-437d-9133-1bfaf955c80a.
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This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within both organic and inorganic semiconductors. Photoluminescent polymers, highly conducting polymers and nanoscale inorganic semiconductors have been investigated using state-of-the-art ultrafast optical techniques, to provide information on the sub-picosecond photoexcitation dynamics in these systems. The influence of dimensionality on the excitation transfer dynamics in a conjugated polymer blend is studied. Using time-resolved photoluminescence spectroscopy, the transfer transients both for a three-dimensional blend film, and for quasi-two-dimensional monolayers formed through intercalation of the polymer blend between the crystal planes of a SnS2 matrix have been measured. A comparison of the experimental data with a simple, dimensionality-dependent model is presented, based on point dipole electronic coupling between electronic transition moments. Within this approximation, the energy transfer dynamics are found to adopt a three-dimensional character in the solid film, and a two-dimensional nature in the monolayers present in the SnS2 -polymer nanocomposite. The time-resolved conductivity of isolated GaAs nanowires has been investigated by optical-pump terahertz-probe time-domain spectroscopy. The electronic response exhibits a pronounced surface plasmon mode that forms within 300 fs, before decaying within 10 ps as a result of charge trapping at the nanowire surface. The mobility has been extracted using the Drude model for a plasmon and is found to be remarkably high, being roughly one third of that typical for bulk GaAs at room-temperature and indicating the high quality and low bulk defect density in the nanowires studied. Finally, the time-resolved conductivity dynamics of photoexcited polymer-fullerene bulk heterojunction blends for two model polymers, P3HT and MDMO-PPV, blended with PCBM are presented. The observed terahertz-frequency conductivity is characteristic of dispersive charge transport for photoexcitation both at the π−π* absorption peak (560 nm for P3HT), and significantly below it (800 nm). The photoconductivity at 800 nm is unexpectedly high, which is attributed to the presence of a charge transfer complex. In addition, the excitation-fluence dependence of the photoconductivity is studied over more than four orders of magnitude. The time-averaged photoconductivity of the P3HT:PCBM blend is over 20 times larger than that of P3HT, indicating that long-lived positive polarons are responsible for the high photovoltaic efficiency of polymer:fullerene blends. At early times (~ ps) the linear dependence of photoconductivity upon fluence indicates that interfacial charge transfer dominates as an exciton decay pathway, generating charges with mobility of at least ~0.1cm2 V−1 s−1. At later times, a sub-linear relationship shows that carrier-carrier recombination effects influence the conductivity on a longer timescale (> 1 μs).
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Pestov, Dmitry Sergeyevich. "Detection of bacterial endospores by means of ultrafast coherent raman spectroscopy." Texas A&M University, 2008. http://hdl.handle.net/1969.1/85958.
Full textAbstract:
This work is devoted to formulation and development of a laser spectroscopic technique
for rapid detection of biohazards, such as Bacillus anthracis spores. Coherent anti-Stokes
Raman scattering (CARS) is used as an underlying process for active retrieval of
species-specific characteristics of an analyte. Vibrational modes of constituent molecules
are Raman-excited by a pair of ultrashort, femtosecond laser pulses, and then probed
through inelastic scattering of a third, time-delayed laser field.
We first employ the already known time-resolved CARS technique. We apply it
to the spectroscopy of easy-to-handle methanol-water mixtures, and then continue
building our expertise on solutions of dipicolinic acid (DPA) and its salts, which happen
to be marker molecules for bacterial spores. Various acquisition schemes are evaluated,
and the preference is given to multi-channel frequency-resolved detection, when the
whole CARS spectrum is recorded as a function of the probe pulse delay. We
demonstrate a simple detection algorithm that manages to differentiate DPA solution
from common interferents. We investigate experimentally the advantages and
disadvantages of near-resonant probing of the excited molecular coherence, and finally
observe the indicative backscattered CARS signal from DPA and NaDPA powders. The possibility of selective Raman excitation via pulse shaping of the preparation pulses is
also demonstrated.
The analysis of time-resolved CARS experiments on powders and B. subtilis
spores, a harmless surrogate for B. anthracis, facilitates the formulation of a new
approach, where we take full advantage of the multi-channel frequency-resolved
acquisition and spectrally discriminate the Raman-resonant CARS signal from the
background due to other instantaneous four-wave mixing (FWM) processes. Using
narrowband probing, we decrease the magnitude of the nonresonant FWM, which is
further suppressed by the timing of the laser pulses. The devised technique, referred to as
hybrid CARS, leads to a single-shot detection of as few as 104 bacterial spores, bringing
CARS spectroscopy to the forefront of potential candidates for real-time biohazard
detection. It also gives promise to many other applications of CARS, hindered so far by
the presence of the overwhelming nonresonant FWM background, mentioned above.
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Makarov, Nikolay Sergeevich. "Ultrafast two-photon absorption in organic molecules quantitative spectroscopy and applications /." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/makarov/MakarovN0510.pdf.
Full textAbstract:
This dissertation explores quantitative two-photon absorption spectroscopy to relate molecular structure with optical properties of organic chromophores. The dissertation describes an advanced fluorescence-based technique for reliable measurements of the two-photon spectra and cross sections. To facilitate the measurements it establishes a set of reference compounds measured with a 15% absolute accuracy covering a broad range of excitation and fluorescence wavelengths. The dissertation shows that in many cases the few-essential-levels model can be successfully applied for the description and interpretation of two-photon absorption spectra and cross sections, at least for the low-energy transitions. The dissertation presents examples of applications of two-photon absorption for volumetric optical storage and cancer tumor detection. It describes the basic principles of the two-photon absorption-based optical memory and limitations imposed on two-photon sensitivity of photochromic materials by a necessity of fast access to the data. It also proposes a novel technique for sensitive detection of cancer cells by using two-photon excitation of near-IR fluorescence of a commercial dye and discusses the mechanisms responsible for differentiation between the normal and the cancer cells. The methods described in this dissertation can be applied to understanding the relations between structure and two-photon absorption strength of individual transitions of organic and biological chromophores, which can be used for design of new materials, maximally adapted for particular applications.
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Lorenz, Virginia O. "Ultrafast spectroscopy of non-Markovian dynamics in a dense atomic vapor." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3256379.
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Strüber, Christian [Verfasser]. "Ultrafast coherent control and multidimensional spectroscopy on the nanoscale / Christian Strüber." Bielefeld : Universitätsbibliothek Bielefeld, 2014. http://d-nb.info/1048176096/34.
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Wolpert, Christian [Verfasser], and Markus [Akademischer Betreuer] Lippitz. "Ultrafast spectroscopy of single quantum dots / Christian Wolpert. Betreuer: Markus Lippitz." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2012. http://d-nb.info/1026242347/34.
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Teo, Stephanie M. "Developments in time-resolved ultrafast imaging and spectroscopy at terahertz frequencies." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92650.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 231-244).
Prior to the advent of high energy pulsed femtosecond lasers, the field of terahertz (THz) spectroscopy was stagnated by the lack of both high power THz sources and sensitive THz detectors. Over the past few years, it has become more 'routine' to generate and detect THz radiation between 0.1-10 THz, but there remains much room for improvement. In this work, I describe recent developments in THz detection methodology, both in a waveguide platform and in a more typical free space geometry. In the waveguide approach, THz generation, detection, and manipulation is self-contained in an on-chip system that we term the polaritonics platform, which simply consists of a single slab of an electro-optic (EO) crystal called lithium niobate. Due to the experimental geometry, we can conduct time-resolved phase-sensitive imaging of the propagating THz waves in the crystal. Alternatively, more conventional THz spectroscopy requires free space propagation between generation and detection such that a sample could be interrogated if placed between them. Within this thesis, I present improvements in spatial resolution and signal-to-noise (S/N) to two time-resolved THz imaging instruments on the polaritonics platform: phase contrast imaging and polarization gating imaging. Across both techniques, we attained a best image resolution of less than 1.5 pm (< A/100 at 0.5 THz), which is needed for studying very fine structures and near-fields in the THz regime, and a lowest noise floor of 0.12%, which is attractive for measuring small signals. We used THz imaging to explore wave behavior in metal-clad waveguide systems by employing indium tin oxide (ITO), which is a conductor at THz frequencies, but transparent at visible frequencies. We deemed ITO to behave similarly to an ideal metal, despite its low electrical conductivity. This presents the possibility of fabricating transparent THz-resonant metallic microstructures for near-field studies. Furthermore, we studied leaky wave behavior in the metal-clad waveguides, which presents a means for coupling THz radiation out of the waveguide. Lastly, I describe recent developments in free space THz detection, which traditionally consists of a time-intensive optically gated measurement in a pump-probe geometry called EO sampling. Unfortunately, this method is not conducive to measurements of irreversible processes or measurements that involve resolving an additional time axis such as in twodimensional (2D) spectroscopy experiments. In the new methodology that is discussed here, we instead acquire a THz time trace in a single laser pulse using a pair of transmission-mode glass echelon optics. We demonstrate that this single-shot method is a robust alternative to conventional scanning EO sampling that can quantitatively record THz field temporal profiles with the same S/N approximately 20 times faster than the conventional method. As a prototype 2D measurement, we applied the single-shot method to an optical pump- THz probe study of a indirect bandgap semiconductor, tin sulfide (SnS), which is currently being investigated as a material for solar cell technology. The 2D measurement made it possible to characterize carrier lifetimes and photoconductivity at THz frequencies as a function of carrier relaxation time. This initial demonstration is only the beginning of future exploration of a wide variety of systems, where we intend to extend the technique towards 2D Fourier transform THz spectroscopy to unravel behavior too complex to be resolved by linear spectra.
by Stephanie M. Teo.
Ph. D.
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Mandal, Aritra. "Vibrational dynamics of aqueous hydroxide solutions studied using ultrafast infrared spectroscopy." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97983.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2015.Cataloged from PDF version of thesis. Vita.
Includes bibliographical references.
Liquid water possesses an extended network of hydrogen bonds that is responsible for many of its interesting properties. Mobility of hydroxide ions in aqueous solutions is much higher compared to the ions of similar size and charge density. A proton can efficiently move from a neighboring water molecule to the hydroxide ion due to the presence of hydrogen bonds, resulting fast structural diffusion of the ion. On the other hand, this hydrogen bonding network of water undergoes fluctuations on femtoseconds to picoseconds timescale, influencing the intertwined hydroxide transport process. Studying the influence of water's hydrogen bonding network on the proton transport process in aqueous hydroxide solutions is experimentally challenging, largely due to the lack of a suitable technique that is sensitive to the changes in the system on few tens of femtoseconds timescale. Vibrations in aqueous hydroxide solutions are sensitive to the strength of hydrogen bonding and hence vibrational frequencies, intensities and line shapes are closely associated with the structure and dynamics of the hydroxide ions. In this thesis, we have employed ultrafast infrared spectroscopy in conjunction with theoretical modeling to understand the nature of the vibrations and their dynamics in aqueous hydroxide solutions. The infrared spectra of aqueous solutions of NaOH and other strong bases exhibit a broad continuum absorption for frequencies between 800 and 3500 cm-¹, which is attributed to the strong interactions of the hydroxide ion with its solvating water molecules. This continuum absorption has limited distinguishable features whose molecular origin holds the key in explaining the vibrational dynamics. We have performed ultrafast transient absorption and 2DIR experiments on aqueous NaOH solutions, by exciting the O-H stretch vibrations and probing the response from 1350-3800 cm-¹, using a newly developed sub-70 fs broadband infrared source. By probing the entire mid-infrared continuum absorption of aqueous hydroxide solutions with ultrafast pulses, the broadband infrared source allows us to monitor time-dependent changes in this broad spectral window. These experiments, in conjunction with harmonic vibrational analysis of OH-(H₂O)₁₇ clusters, reveal that O-H stretch vibrations of aqueous hydroxides arise from coupled vibrations of multiple water molecules solvating the ion. These delocalized vibrations cannot be distinguished based on the local structure of the hydroxide ion. However, they can be classified according to the symmetry defined by the relative phase of vibrations of the O-H bonds hydrogen bonded to the ion. In general, we find the asymmetric O-H stretch vibrations to be more intense and shifted to lower frequencies compared to the symmetric ones. Analysis of transient absorption and waiting time dependent 2DIR spectroscopy shows that the vibrations in aqueous hydroxide solutions relax on 100-300 fs timescale. Alongside, the O-H stretch vibrations originating from the bulk-like water molecules as well as the asymmetric O-H stretch vibrations of the water molecules solvating the hydroxide ion lose their frequency memory within 160-180 fs. Such loss in frequency memory on similar timescales is likely to happen through migration of vibrational excitation between two types of O-H stretch vibrations. Spectral features in strongly hydrogen bonded systems like water and aqueous hydroxide solutions are very broad, particularly the induced absorption features in the transient absorption and 2DIR spectra. With the development of broadband mid-infrared pulses, we are able to detect nonlinear response of these systems in the frequency window of 1350-3800 cm-¹, observing >1700 cm-¹ broad induced absorption features. Qualitatively, strong coupling between intra- and intermolecular vibrations lead to such broadening. In order to explain the experimental results, we have developed a self-consistent phenomenological model that consists of an intramolecular and an intermolecular vibration, with strong nonlinear coupling between them. We find that the experimental results are reproduced when the coupling between the vibrations is strong enough to yield eigenstates with mixed intra- and intermolecular vibrational character. In such scenarios, the identities of individual intra- and intermolecular vibrational modes are lost.
by Aritra Mandal.
Ph. D.
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O'Keefe, Guy Edward. "Ultrafast optical spectroscopy of the excited-states of conjugated organic molecules." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627580.
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Simpson, Niall. "Accessing ultrafast protein dynamics through 2DIR spectroscopy of intrinsic ligand vibrations." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26003.
Full textAbstract:
Proteins are complex molecular machines that facilitate the chemical reactions fundamental to life. Their functions are encoded in a linear sequence of amino acids, of which only 20 species are found in nature. Yet the functional and structural diversity accessible through these building blocks is vast. Molecular and atomic-level protein studies have been crucial to our understanding of health and treatment of disease, with increasingly sophisticated experimental and computational methods continuing to provide new information with which to advance medicine. However, the requirement for more detailed understanding of proteins has risen through the emergence of multi-antibiotic-resistant bacteria and also through the potential to design synthetic proteins of novel function. Paradigms of protein function have evolved significantly since early studies, though few all-encompassing descriptions have been proposed, owing to the complex, dynamic structures of these large biomolecules. Presently, the relationship between protein structural motions at different timescales appears to hold vital significance to the elusive aspects of biological mechanisms. No single measurement technique is capable of accessing the multitude of timescales over which protein motions occur, and thus concerted investigation is necessary. Observation of dynamics at the femtosecond-picosecond timescale has only recently become possible through the development of new experimental techniques, allowing a new class of protein motions to be investigated. In this thesis, the advanced technique of two-dimensional infrared spectroscopy (2DIR) is employed to study three biomolecular systems with implications to ubiquitous protein interactions. The aims of these investigations are, firstly, to demonstrate the suitability of 2DIR spectroscopy in gathering novel dynamic information from biological systems that is not accessible via other methods, and secondly, to derive the potential physical significance of these dynamics as they relate to biological function. A description of the underlying theory of 2DIR is presented in this Chapter, along with the considerations that must be made in the application of such a technique to complex biological case-studies. In Chapter (2), descriptions are given for the experimental setups used to acquire infrared spectra, specifically, Fourier transform infrared (FTIR), pump-probe and 2DIR spectroscopies. In Chapter (3) the catalytic-site dynamics of two closely-related haem proteins are each studied by monitoring the vibrational evolution of a nitric oxide (NO) probe molecule bound to the haem centre. A comparison of the active site dynamics is performed in order to correlate the observed differences with discrepancies between the protein reaction mechanisms. Chapter (4) explores the potential of a coenzyme with high protein-binding promiscuity to serve as an intrinsic reporter of the dynamics that occur at substrate binding sites. Infrared analysis and categorisation of the free coenzyme molecule is performed in order to establish its effectiveness as a probe. In Chapter (5), method-development strategies are proposed for the extraction of 2DIR data from large, complex protein-protein systems, with the objective of expanding the range of interactions on which 2DIR can effectively report. Both well-established and novel strategies are employed, and the potential and limitations of the technique are discussed in the context of these demanding case-studies. Chapter (6) draws together conclusions and an overview of progress made and discusses future directions.
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Mier, Lynetta M. "Monitoring Electron Transfer Reactions using Ultrafast UV-Visible and Infrared Spectroscopy." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1339440446.
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Khubaibullin, Ilnur. "Pyridinium Salts As Electron Traps: An Ultrafast Transient Absorption Spectroscopy Study." Bowling Green State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1478704646450194.
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Allerbeck, Jonas [Verfasser]. "Ultrafast Multidimensional Spectroscopy of Semiconductors and Strongly Correlated Materials / Jonas Allerbeck." Konstanz : KOPS Universität Konstanz, 2020. http://d-nb.info/1220635790/34.
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Rivett, Jasmine Pamela Helen. "Charge carrier dynamics of lead halide perovskites probed with ultrafast spectroscopy." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275095.
Full textAbstract:
In this thesis, we investigate the nature of charge carrier generation, relaxation and recombination in a range of lead halide perovskites. We focus on understanding whether the photophysical behaviour of these perovskite materials is like that of highly-ordered inorganic crystalline semiconductors (exhibiting ballistic charge transport) or disordered molecular semiconductors (exhibiting strong electron-phonon coupling and highly localised excited states) and how we can tune these photophysical properties with inorganic and organic additives. We find that the fundamental photophysical properties of lead halide perovskites, such as charge carrier relaxation and recombination, arise from the lead halide lattice rather than the choice of A-site cation. We show that while the choice of A-site cation does not affect these photophysical properties directly, it can have a significant impact on the structure of the lead halide lattice and therefore affect these photophysical properties indirectly. We demonstrate that lead halide perovskites fabricated from particular inorganic and organic A-site cation combinations exhibit low parasitic trap densities and enhanced carrier interactions. Furthering our understanding of how the photophysical properties of these materials can be controlled through chemical composition is extremely important for the future design of highly efficient solar cells and light emitting diodes.