Dissertations / Theses on the topic 'Coherent spectroscopy'
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1
Beaman, R. A. "Two beam coherent spectroscopy." Thesis, Cardiff University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379609.
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Quilter, John Howard. "Coherent spectroscopy of single quantum dots." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/7711/.
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This thesis presents experiments carried out into the coherent properties of charge carriers confined within a single InGaAs/GaAs quantum dot. Specifically the ground state - single exciton qubit system is controlled with ultrafast optical pulses and then the population of the dot is measured by a high-sensitivity photocurrent detection technique. There are two principal results of these experiments, firstly by modulating the bias applied to the quantum dot diode, the detection efficiency of the photocurrent measurement technique is enhanced. The enhancement is possible as the modulated bias allows fast switching of the voltage-dependent carrier tunneling rates. Secondly, when the transition is addressed by an intense, positively detuned laser, the qubit system can be driven to a population inversion. This occurs due to phonon-assisted relaxation of the optical dressed states of the system. Here, the rapid thermalization due to the exciton-phonon interaction actually enables the population inversion, instead of simply being a source of decoherence.
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Viranna, Narendra Balaguru. "Coherent anti-Stokes Raman spectroscopy of diamond." Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/26229.
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Experiments were performed to investigate Coherent Anti-Stokes Raman Scattering (CARS) in diamond. Aspects of this type of non-linear scattering are presented theoretically, and various experimental configurations were attempted in order to study them. These included the dependence of the CARS signal intensity on the intensities of the two exciting frequency-doubled Nd:YAG (pump) and dye (Stokes) lasers, the variation of the CARS signal polarization as a function of the lasers' polarization, and the dependence of the CARS signal intensity on the phase mismatch of the laser beams. The phase mismatch measurement confirmed the predicted sinc² nature of the CARS signal intensity, while· the polarization measurements provided new information on the ratio of the non-vanishing components of the cubic susceptibility x³ of diamond. The CARS signal intensity was found to change linearly with the dye laser intensity and quadratically with the Nd: Y AG laser intensity. The CARS signal was found at the predicted 1332 cm⁻¹ shift from the doubled Nd:YAG emission, and its linewidth of 1.2 cm⁻¹ is in agreement with the spontaneous Raman linewidth.The spectral data were fitted to a modified Voigt profile containing the non-resonant cubic susceptibility contribution, and this allowed us to establish the ratio of the resonant and non-resonant parts of x³. An attempt to generate Stimulated Raman Scattering in diamond was unsuccessful.
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Kirkbride, James M. R. "Coherent transient spectroscopy with quantum cascade lasers." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c7b897e5-052f-4c15-a3c9-f95ca3b56d70.
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This thesis is concerned with coherent effects in high resolution mid-infrared gas phase spectroscopy using quantum cascade lasers (QCLs). An introductory chapter explains the importance of QCLs as radiation sources in the mid-infrared region of the spectrum and goes on to detail their development and structure. A discussion of coherent effects in spectroscopy follows, leading into the second chapter which discusses the theories relevant to the experimental sections of the thesis. In chapter 2 the theory underpinning direct and velocity selective, Doppler-free spectroscopy is discussed and a density matrix formalism is followed to derive the equations of motion that govern coherent excitation effects in two-level systems. In the final part of the chapter this treatment is extended to three-level systems. The equations derived in this chapter form the basis of quantitative interpretations of the phenomena observed in experimental data and presented in the remainder of the thesis. In chapter 3 the characterisation of a high power, narrow linewidth QCL is carried out. This laser is then used to perform direct and sub-Doppler resolution spectroscopy on NO, demonstrating non-linear absorption at high laser intensities and providing a measurement of the laser linewidth in the limit of slow frequency tuning. As the slow tuning rate increases, evidence of coherent transient effects is presented and density matrix theory used to model this behaviour. The data presented include the first observations of asymmetric Lamb dips and the onset of rapid passage oscillations from a Lamb dip. Pump-probe experiments on NO, utilising two cw QCLs are presented in chapter 4. The high level of velocity selection afforded by QCL excitation leads to coherent transient signals at far lower probe scan rates than previously reported. The effect of altering both the scan rate and the gas pressure and the importance of hyperfine structure are presented. A radio frequency noise source applied to one of the lasers is shown to broaden the laser linewidth, leading to rapid dephasing. A two-colour polarisation spectroscopy experiment is also presented which allows the measurement of both the absorption and the Doppler-free dispersion signals and the three-level density matrix formalism presented at the end of chapter 2 used to model the non-linear response of the system. The final chapter details the use of an acousto-optic modulator to create a pulse of mid-IR light using a cw QCL and the application of this to time resolved pump-probe spectroscopy. This capability suggests the prospect of achieving coherent population transfer by stimulated Raman adiabatic passage (STIRAP) using two such pulses. Simulations based on a simple three-level model and including Zeeman coherences are presented, which take the measured properties of the lasers used in this thesis as inputs to predict the potential population transfer achievable in NO as well as providing useful information about the angular momentum polarisation of the excited molecules. An experimental realisation of STIRAP would require the lasers to be stabilised, and so the final part of the chapter details experimental attempts to achieve stabilisation of an external cavity QCL, and suggests future avenues for improved implementation.
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Turner, Daniel Burton. "Investigating exciton correlations using coherent multidimensional optical spectroscopy." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62037.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Vita. Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 153-166).
The optical measurements described in this thesis reveal interactions among bound electron-hole pairs known as excitons in a semiconductor nanostructure. Excitons are quasiparticles that can form when light is absorbed by a semiconductor. Exciton interactions gained prominence in the 1980s when unexpected signals were observed in studies of carrier dynamics. The presence of exciton interactions in semiconductors motivated an ongoing, focused research effort not only because the materials had valuable commercial applications but also because the interactions could be used to test fundamental theories of many-body physics. Laser light provides a coherent electric field with a well defined phase. In linear spectroscopy, an electric field that is resonant with an exciton transition will induce coherent oscillations of electronic charge density. The charges will oscillate at the transition frequency with a well defined phase, and these oscillations will radiate a signal that has an amplitude proportional to the incident field amplitude and has the same direction as the incident light. If the laser light is intense, its field may induce a high density of excitons, and the field can interact with those excitons to induce transitions to higher-energy states composed of multiple interacting excitons. Many-body interactions among the excitons can predictably modify--or unpredictably scramble--the quantum phase of the exciton. The interactions can produce signals that have amplitudes proportional to high powers of the incident field amplitude, and the signal fields often propagate in directions different than the incident field. The signal fields contain information--often encoded in their phases--that can reveal the nature of the higher-energy states and the many-body interactions that produced them. Thus, many-body interaction studies rely on measurements of exciton phases that are reflected in the optical phases of coherent signals. These measurements require a tool that can detect optical coherence before the exciton phases are scrambled by the environment. Coherent ultrafast optical spectroscopy is that tool. The spectra displayed in this work were measured by an experimental apparatus that separates the electric fields as needed into different laser beams with controllable directions; it controls the optical phase, arrival time, and polarization of the femtosecond light pulse(s) in each of those beams; it then recombines all of the beams at the 5 sample to generate the signal field; and finally it measures the signal field, including its phase. Using this instrument, we isolated--with a high degree of selectivity--signals that arose from different numbers of field interactions and from different microscopic origins using various beam geometries and pulse timing sequences. In this thesis, we present electronic spectra measured at varying orders in the electric field to isolate and measure the properties of excitons and their many-body interactions. As the number of electric fields is increased and the resulting higherorder signals are generated, interactions involving increasing numbers of particles can be measured. The vast majority of previous work focused on the interactions manifest in third-order signals. This thesis not only includes new insights gained from third-order signals, but also includes new phenomena observed in fifth-order and seventh-order signals. We measure signals due to four-particle correlations in the form of bound biexcitons and unbound-but-correlated exciton pairs. We also measure signals due to six-particle correlations in the form of bound triexcitons. Although we searched for them, there were no signals due to eight-particle correlations, indicating that the set of multiexciton states truncates. We thus measured the properties and the extent of many-body interactions in this system. The spectra presented here reveal a large set of excitonic many-body interactions in GaAs quantum wells and answer questions about the many-body interactions posed decades ago. The optical apparatus constructed to perform these measurements will soon be used to measure correlations in a range of systems, including other semiconductors and their nanostructures, molecular aggregates, molecules, and photosynthetic complexes. Because future technologies such as entangled photon sources, advanced photovoltaics, and quantum information processing will rely on these types of materials and their many-body correlations, it is important to develop techniques to measure their microscopic interactions directly.
by Daniel Burton Turner.
Ph.D.
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Somma, Carmine. "Coherent Multidimensional Off-resonant THz Spectroscopy on Semiconductors." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18512.
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Zum ersten Mal konnte die kohärente Erzeugung von ultrakurzen Pulsen mit Feld stärken im MV/cm Bereich mit einem Spektralbereich von 0.1-30 THz im organischen Kristall DSTMS. Kohärente mehrdimensionale Terahertzspektroskopie (CMTS) hat sich zu einer wichtigen Methode zur Untersuchung der niederenergetischen Anregungen von Halbleitern and deren kohärenter Dynamik entwickelt. Eine neuartige CMTS Methode mit drei phasenstarren, zueinander zeitverzögerten Terahertzpulsen wurde entwickelt. Sie beruht auf der kollinearen Wechselwirkung der Pulse mit der Probe, sodass verschiedene Ordnungen des nichtlinearen Signals in gleicher Richtung emittiert werden und deshalb gleichzeitig gemessen werden können. Amplitude und Phase des nichtlinearen Signals können durch elektro-optisches Abtasten vermessen werden, wodurch die zeitliche Entwicklung der kohärenten Wechselwirkungen in Echtzeit untersucht werden kann. CMTS erlaubt zusätzlich die eindeutige Zerlegung des nichtlinearen Signals in die verschiedenen nichtlinearen Ordnungen in der jeweiligen mehrdimensionalen Frequenzdomäne. Die nichtlineare, nicht-resonante Antwort zweier undotierter Halbleiter, des Ferroelektrikums Lithiumniobat (LiNbO3) und Indiumantimonids (InSb) kann mit dieser neuartigen Methode untersucht werden. In LiNbO3 wird das nichtlineare Signal durch einen Femtosekunden nichtlinearen Verschiebestrom (SC) hervorgerufen. SC wird durch die gebrochene Inversionssymmetrie des Kristalls in Verbindung mit einer ultraschnellen Dephasierung der feldinduzierten, kohärenten interband-Polarisation hervorgerufen. Die Dephasierung
der interband-Polarisation erlaubt das Tunneln von Elektronen vom Valenzband in
das Leitungsband. In InSb wird das kohärente Signal durch sowohl zwei-Phonen als
auch zwei-Photonen interband-Anregungen erzeugt. Die impulsive Anregung einer
kohärenten zwei-Phononen Polarisation wird durch das große Übergangsdipolmoment
von InSb verstärkt, was zu deutlich größeren Amplituden der Polarisation als im linearem
Regime führt.For the first time, the coherent generation of ultrashort MV/cm field pulses with a spectrum covering the frequency range 0.1-30 THz is demonstrated in the organic crystal DSTMS. Coherent multidimensional terahertz spectroscopy (CMTS) has become a prominent technique for, e.g., driving low-energy excitations in semiconductors and monitoring their coherent dynamics. A novel CMTS technique using three phase-locked inter-delayed THz pulses is implemented. It relies on a collinear interaction of the pulses with a sample, so that different contributions to the nonlinear signal are emitted in the same direction, and thus can be measured all at once. Phase-resolved detection by electro-optic sampling allows for measuring amplitude and absolute phase of the nonlinear signal, thereby enabling to investigate the evolution of coherent interactions between quantum excitations in real time. In CMTS, the nonlinear signal is dissected into the distinct nonlinear contributions in the corresponding multidimensional frequency domain. This novel technique is applied to study the nonlinear off-resonant response of two undoped bulk semiconductors, the wide-bandgap ferroelectric lithium niobate (LiNbO3) and the narrow-bandgap indium antimonide (InSb). In LiNbO3, the nonlinear signal is generated by a femtosecond nonlinear shift current (SC), a distinctive characteristic of the bulk photovoltaic effect. The SC stems from the lack of inversion symmetry and the ultrafast dephasing of the field-induced interband coherent polarization due to a sufficiently high decoherence rate, which enables tunneling of electrons from the valence to the conduction band. In InSb, the nonlinear signal is caused by the coherent response on both the two-phonon and two-photon interband excitations. The impulsive generation of the two-phonon coherent polarization is enhanced by the large interband transition dipole of InSb, resulting in much larger polarization amplitudes than in the regime of linear response.
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Branderhorst, Matthijs Pieter Arie. "Coherent control of decoherence." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670035.
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Jerebtsov, Serguei Nikolaevich. "Femtosecond time-resolved spectroscopy of coherent oscillations in nanomaterials." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1358.
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Arlt, Sebastian. "Coherent femtosecond spectroscopy of exciton-continuum interaction in semiconductors /." Zürich, 1999. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13475.
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Stowe, Matthew C. "Direct frequency comb spectroscopy and high-resolution coherent control." Connect to online resource, 2008. 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:3315768.
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Dobrev, Georgi. "Laser spectroscopy for coherent manipulation and state-specific probing of atoms and molecules." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1083/document.
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Cette thèse décrit le travail expérimental sur différentes techniques visant l'obtention du contrôle de l'état quantique d'atomes et de molécules, pour application dans l'informatique quantique, la métrologie et l'astrophysique. Le contrôle cohérent exige des conditions précises de fonctionnement d'un système où la décohérence est minimisée. La construction d'une machine à jet atomique de calcium est présentée comme l'élément de base d'expériences où des schémas d'excitation laser choisis permettront de préparer de façon robuste un état quantique au moyen d'impulsions composites. La deuxième section décrit ma contribution pour améliorer la stabilité de fréquence relative de l'horloge à fontaine de cesium CSF2, à l'institut allemand de métrologie. Un piège magnéto-optique modifié produit un faisceau d'atomes de césium lents. Ils sont préparés dans un état noir spécifique puis sont efficacement transférés à la mélasse optique de la fontaine. L'augmentation du nombre d'atomes participant ainsi au cycle d'horloge améliore sa stabilité d'un facteur 6. La troisième section concerne les spectres de molécules NiH et FeH. Plusieurs sources pour leur production en laboratoire ont été développées et testées. Une expérience d'absorption laser différentielle et une technique de spectroscopie intra-cavité sont appliquées aux molécules faiblement absorbantes NiH, afin d'obtenir leurs coefficients d'absorption dans le rouge. La réponse Zeeman de la molécule FeH (une sonde du champ magnétique des étoiles froides) dans le proche infrarouge est étudiée par spectroscopie laser de précision afin d'établir des facteurs Landé pour 33 niveaux rovibrationnelles de l'état électronique F 4?This thesis describes experimental work on different techniques aiming to achieve control of the quantum state of atoms and molecules, envisaging applications in quantum computing, metrology and astrophysics.Successful coherent control requires careful design of operating conditions for a system where decoherence is minimized. The construction of a calcium atomic beam is presented as a necessary element in experiments with laser excitation schemes chosen to provide high-fidelity preparation of a quantum satate by means of composite pulses. The second section describes my contribution to the improvement of the relative frequency stability of the Cs fountain clock CSF2 at the German institute of metrology. A modified magneto-optical trap is employed to form a beam of slow cesium atoms. They are prepared in a specific dark state and subsequently are efficiently transferred to the optical molasses of the fountain. Increasing number of atoms participating in the clock cycle in this way improves the stability of the clock by a factor of 6.The third section is concerned with spectra of metal hydride molecules NiH and FeH. Several sources for production of these molecules in laboratories were developed and tested. A differential laser absorption experiment and a cavity-enhanced spectroscopy technique are applied on the w??kly absorbing NiH molecules, to obtain absorption coefficients for the red bands of NiH. The Zeeman response of the FeH molecule (a probe for magnetic fields in cool stars) in the near-IR is investigated by precision laser spectroscopy establishing Landé factors for 33 rovibrational levels of the F 4? electronic state
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Demirdöven, Nurettin 1974. "Coherent two-dimensional infrared spectroscopy : a study of coupled vibrations." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17653.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.Vita.
Includes bibliographical references.
This thesis provides an introduction to experimental techniques used in two-dimensional (2D) infrared (IR) spectroscopy, outlines how third-order nonlinear response of a multi-level vibrational system is calculated, and provides a detailed methodology of line shape analysis in 2D spectroscopy. Specific emphasis is given to inherent sensitivity of 2D spectroscopy to correlated spectral broadening. The signatures of highly correlated transition energy fluctuations in a model system of two strongly coupled carbonyl stretching vibrations are reflected by the elongation of the cross peaks along the diagonal of the 2D spectrum. The dynamics of this correlation is monitored by the changes in the 2D line shapes and successfully modeled using a correlated spectral diffusion model. The sensitivity of 2D IR spectroscopy to interactions between multiple vibrational coordinates is also explored in conformationally complex polypeptides and proteins with well-defined secondary structures. 2D IR spectroscopy of β-hairpins and globular proteins with antiparallel (AP) β-sheet domains is studied to identify 2D markers of AP β-sheet conformation. The experiments on β-hairpins and proteins with varying percentage of β-sheet character showed that the formation of cross peaks between the two characteristic vibrational modes of AP β-sheets is a marker of AP β-sheet secondary structure. The intensity, location and line shapes of the cross peaks are qualitatively related to the size, geometry and the conformational variations in the AP β-sheet structure.
by Nurettin Demirdöven.
Ph.D.
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Mahmood, Fahad Ph D. Massachusetts Institute of Technology. "Femtosecond spectroscopy of coherent phenomena in quantum materials : a dissertation." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104461.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 217-236).
Quantum materials are solids that cannot be described by the single-particle band models of conventional condensed matter physics. Rather strong inter-particle interactions and coupling between various degrees of freedom (charge, spin, orbital and lattice) lead to emergent phases such as high-temperature superconductivity, spin and charge density wave ordering and topologically protected 2D Dirac fermions. In the time-resolved experiments in this work, an initial laser 'pump' pulse drives the sample out-of-equilibrium by manipulating the electronic band structure, generating quasi-particles and/or exciting specific collective modes. The resulting dynamic changes are then tracked as a function of time by using two different spectroscopic tools: transient reflectivity and time and angle resolved photoemission (Tr-ARPES). One approach is to perturb the system gently (low pump intensity) to preserve the underlying order. Transient reflectivity experiments are done in this weak perturbation regime to study the following phenomena: (1) Collective excitations (amplitude and phase mode) of the fluctuating charge density wave order in the cuprate superconductor La₂-xSrxCuO₄; (2) Decay dynamics of valley polarized excitons in the monolayer transition metal dichalcogenide MoSe₂; and (3) a confinement-deconfinement transition of single-particle excitations in the spin-orbit assisted Mott insulator Na₂IrO₃. In the opposite regime (strong perturbation), it is possible to drive electronic materials into non-equilibrium phases with fundamentally different properties than in equilibrium. This work uses mid-IR pump pulses to directly couple photons to an electronic system to create hybrid electron-photon states. In this case, the oscillating electric field of the pump causes Dirac fermions to experience a time-periodic potential to generate Floquet-Bloch states which repeat in both energy and momentum. These and other similar photo-induced states are observed and characterized using Tr-ARPES on the topological insulators Bi₂Se₃ and Bi₂Te₃.
by Fahad Mahmood.
Ph. D.
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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.
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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.
15
Brunner, Daniel. "Laser spectroscopy of coherent quantum states in single quantum dots." Thesis, Heriot-Watt University, 2010. http://hdl.handle.net/10399/2350.
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Laser spectroscopy was used for studying single charge-tunable InAs quantum dots (QD). The spectroscopy system consisted of a high resolution microscope combined with a solid immersion lens, a grating spectrometer and an in-situ detector to study the homodyne signal of the resonant laser and the QD. Low density QD samples were fabricated, which allowed spectral isolation of individual QDs. A modulation technique was used for noise rejection. Resonant absorption spectroscopy was used for directly probing transitions between ground and excited QD states. Lineshapes and signal strength were linked to life and coherence times of QD states. A theoretical model was developed combining coherent and non coherent processes in a master equation. Positively and negatively doped sample structures enabled spectroscopy of negatively, neutral and positively charged excitons. The relaxation time of hole spin ground states in a single QD was probed using resonant excitation in a magnetic eld parallel to the growth direction. Optical selection rules enable control over hole spin orientation. Hole spin relaxation times were studied from zero to ve Tesla, with relaxation times of di erent QDs ranging from 200 s to 1 ms. No signi cant in uence of the external magnetic eld on the hole spin relaxation time was found. A hole spin initialisation delity close to 100 % was achieved. Readout of resonantly created QD states was realised via a new microscope system. This dark eld microscope utilised spatial and polarisation ltering techniques to suppress the excitation laser by up to six orders of magnitude. Both ltering devices were included in the standard microscope, making it a highly practical and versatile system. Collected QD emission exceeded the resonant laser background by a factor of 100 for an unsaturated X1 transition. Pump-probe spectroscopy of the 3-level biexciton system was carried out, with the back scattered signal collected in re ection allowing spectral ltering via a grating spectrometer. The recorded probe spectrum revealed Autler-Townes splittings for high pump laser intensities, demonstrating the coherent superposition of QD exciton states. Swapping the pump probe geometry revealed weak quantum interferences. Spectroscopy of hole spin ground states in an in-plane magnetic eld created a coherent superposition of hole spin ground states via a -system. The resulting quantum interference between hole spin states resulted in the creation of a dark state. This experiment is known in quantum optics as coherent population trapping. The extracted lower bound of the hole spin coherence time was 1 s with greater than 40 % probability, demonstrating the enormous potential of hole spins in QDs for quantum information processing as well as for quantum optical experiments.
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Payne, Lukas M. "Optical extinction and coherent multiphoton micro-spectroscopy of single nanoparticles." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/87182/.
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Nanoparticles of many varieties are increasingly studied for use in the physical, chemical, and biological sciences. Metallic nanoparticles exhibit morphology-dependent localised surface plasmon resonances (LSPR), which couple to propagating light, and manifest as a resonant particle polarisability at the LSPR frequency. These resonances can be harnessed for a variety of applications. Many of these applications require characterisation of NP properties, such as their optical response, summarised by the ab- sorption and scattering cross sections. Quantitative measurement of individual NPs is technically difficult, and ensemble measurement techniques, such as absorption spectroscopy, are frequently employed. However, individual NP properties can vary significantly, within the ensemble. In this work, we present a novel, and easy to implement, wide-field extinction microscopy technique, capable of analysing hundreds of nanoparticles simultaneously. Using this technique, we are able to characterise individual gold nanoparticles down to 5 nm diameter, and collate the data to produce ensemble statistics. Furthermore, we developed a program for the rapid analysis of the acquired image, enabling implementation by others in a cost-effective and efficient manner. Using the wide-field extinction technique, we have studied several sizes of gold, platinum, silver, and diamond nanoparticles. We used gold nanoparticles to pro- vide a proof of concept, and found good agreement with the literature. We also present an experimental investigation towards an in-vitro plasmon ruler. Coupled metallic NPs exhibit a LSPR, which is dependent on interparticle distance. The four-wave mixing technique we employ is phase-sensitive, allowing measurement of the shift of the res- onance frequency of gold NPs. To provide proof-of-principle of the plasmon ruler, we correlatively studied gold nanoparticle dimers, with transmission electron microscopy, and four-wave mixing microscopy. In this way, we obtained a direct measure of the interparticle distance, and could relate it to the measured phase shift in four-wave mixing.
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Burkart, Johannes. "Optical feedback frequency-stabilized cavity ring-down spectroscopy - Highly coherent near-infrared laser sources and metrological applications in molecular absorption spectroscopy." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY045/document.
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La spectroscopie d'absorption moléculaire est un outil incontournable non seulement pour la physique fondamentale et la métrolgie mais aussi pour des domaines aussi divers que les sciences environnementales, la planétologie ou l'astrophysique. Ces dernières années, des techniques spectroscopiques qui exploitent l'amplification résonnante d'interaction entre lumière laser et molécules dans une cavité optique ont fourni des détectivités exceptionnelles sur l'axe d'absorption, tandis que l'axe de fréquence des spectromètres n'atteignait généralement pas le même niveau de précision.Dans cette thèse, nous avons répondu à ce défi en développant la spectroscopie en cavité par temps de déclin stabilisée en fréquence par rétroaction optique (OFFS-CRDS en anglais). Cette nouvelle technique présente une combinaison unique de stabilité et résolution fréquentielles sub-kHz, d'un niveau d'intensité lumineuse intra-cavité de l'ordre du kW/cm^2, d'une detectivite de 2 x 10^(−13) cm^(−1)Hz^(-1/2) limitée par le bruit de photons, et d'une limite de détection de 8.4 x 10^(−14) cm^(−1) sur une plage spectrale étroite. Ces performances inédites sont dues à l'asservissement de la cavité spectroscopique à un laser balayé en fréquence par modulation à bande latérale unique et stabilisé par rétroaction optique avec une cavité en V de réference ultrastable. Pour transférer la cohérence de ce laser sub-kHz à des lasers plus bruiteux dans d'autres gammes spectrales à travers un peigne de fréquence optique, nous avons exploré une nouvelle méthode de clonage de phase par une correction anticipative à large bande passante et démontré une erreur résiduelle de phase de 113 mrad. En appliquant l'OFFS-CRDS à la spectroscopie du CO2 à 1.6 μm, nous avons obtenu un spectre large bande avec une dynamique de 8 x 10^5, et nous avons déterminé douze fréquences de transition absolues avec une exactitude de l'ordre du kHz en mesurant des Lamb dips sub-Doppler en absorption saturée avec un dispositif équipé d'un peigne de fréquence. Par ailleurs, nous avons procédé à une analyse détaillée des sources d'erreurs systematiques en CRDS et nous avons déduit une formule analytique pour le déclin de cavité non-exponentiel dans un régime faiblement saturé qui est susceptible de contribuer à de futures mesures de moments de transition dipolaire indépendantes de la concentration. Nos résultats ouvrent des perspectives prometteuses pour des applications métrologiques de l'OFFS-CRDS, comme par exemple l'étude de profils de raie poussés, la mesures de rapports isotopiques et la spectroscopie d'absorption saturée extensive dans le proche infrarougeHigh-precision molecular absorption spectroscopy is a powerful tool for fundamental physics and metrology, as well as for a broad range of applications in fields such as environmental sciences, planetology and astrophysics. In recent years, spectroscopic techniques based on the enhanced interaction of laser light with molecular samples in high-finesse optical cavities have provided outstanding detection sensitivities on the absorption axis, while the spectrometer frequency axis rarely met as high precision standards.In this thesis, we addressed this challenge by the development of Optical Feedback Frequency-Stabilized Cavity Ring-Down Spectroscopy (OFFS-CRDS). This novel technique features a unique combination of sub-kHz frequency resolution and stability, kW/cm^2-level intracavity light intensity, a shot-noise limited absorption detectivity down to 2 x 10^(−13) cm^(−1)Hz^(-1/2), as well as a detection limit of 8.4 x 10^(−14) cm^(−1) on a narrow spectral interval. This unprecedented performance is based on the tight Pound-Drever-Hall lock of the ring-down cavity to a single-sideband-tuned distributed-feedback diode laser which is optical-feedback-stabilized to a highly stable V-shaped reference cavity. To transfer the coherence of this sub-kHz laser source to noisier lasers in other spectral regions through an optical frequency comb, we have explored a novel high-bandwidth feed-forward phase cloning scheme and demonstrated a residual phase error as low as 113 mrad. Applying OFFS-CRDS to the spectroscopy of CO_2 near 1.6 μm, we obtained a broadband spectrum with a dynamic range of 8 x 10^5 and retrieved twelve absolute transition frequencies with kHz-accuracy by measuring sub-Doppler saturated absorption Lamb dips with a comb-assisted setup. Furthermore, we have performed a comprehensive analysis of systematic error sources in CRDS and derived an analytic formula for the non-exponential ring-down signal in a weakly saturated regime, which may contribute towards future concentration-independent transition dipole moment measurements. Our results open up promising perspectives for metrological applications of OFFS-CRDS, such as advanced absorption lineshape studies, isotopic ratio measurements and extensive saturated absorption spectroscopy in the near infrared
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Hettich, Mike [Verfasser]. "Investigation of Multilayer Systems by Coherent Acoustic Phonon Spectroscopy / Mike Hettich." München : Verlag Dr. Hut, 2014. http://d-nb.info/1055863508/34.
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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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Marian, Adela Ye Jun. "Direct frequency comb spectroscopy for optical frequency metrology and coherent interactions." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/dissertations/fullcit/3186934.
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Beaudoin, Bertrand Julien. "Homodyne High-harmonic Spectroscopy: Coherent Imaging of a Unimolecular Chemical Reaction." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23173.
Full textAbstract:
At the heart of high harmonic generation lies a combination of optical and collision physics entwined by a strong laser field. An electron, initially tunnel-ionized by the field, driven away then back in the continuum, finally recombines back to rest in its initial ground state via a radiative transition. The emitted attosecond (atto=10^-18) XUV light pulse carries all the information (polarization, amplitude and phase) about the photorecombination continuum-to-ground transition dipolar field. Photorecombination is related to the time-reversed photoionization process. In this perspective, high-harmonic spectroscopy extends well-established photoelectron spectroscopy, based on charged particle detection, to a fully coherent one, based on light characterization. The main achievement presented in this thesis is to use high harmonic generation to probe femtosecond (femto=10^-15) chemical dynamics for the first time. Thanks to the coherence imposed by the strong driving laser field, homodyne detection of attosecond pulses from excited molecules undergoing dynamics is achieved, the signal from unexcited molecules acting as the reference local oscillator. First, applying time-resolved high-harmonic spectroscopy to the photodissociation of a diatomic molecule, Br2 to Br + Br, allows us to follow the break of a chemical bond occurring in a few hundreds of femtoseconds. Second, extending it to a triatomic (NO2) lets us observe both the previously unseen (but predicted) early femtosecond conical intersection dynamics followed by the late picosecond statistical photodissociation taking place in the reaction NO2 to NO + O. Another important realization of this thesis is the development of a complementary technique to time-resolved high-harmonic spectroscopy called LAPIN, for Linked Attosecond Phase INterferometry. When combined together, time-resolved high-harmonic spectroscopy and LAPIN give access to the complex photorecombination dipole of aligned excited molecules. These achievements lay the basis for electron recollision tomographic imaging of a chemical reaction with unprecedented angstrom (1 angstrom= 0.1 nanometer) spatial resolution. Other contributions dedicated to the development of attosecond science and the generalization of high-harmonic spectroscopy as a novel, fully coherent molecular spectroscopy will also be presented in this thesis.
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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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Wituschek, Andreas [Verfasser], and Frank [Akademischer Betreuer] Stienkemeier. "Phase-modulated coherent time-domain spectroscopy in the extreme ultraviolet regime." Freiburg : Universität, 2020. http://d-nb.info/1226657095/34.
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Porter, Fiona M. "A study of temperature measurement using Coherent Anti-Stokes Raman Spectroscopy." Thesis, University of Surrey, 1985. http://epubs.surrey.ac.uk/847913/.
Full textAbstract:
The aim of this work is to increase the applicability of Coherent Anti-Stokes Raman Spectroscopy (CARS) to temperature measurement in practical devices. Particular emphasis is placed on combustion thermometry and high pressure steam systems are also considered. A study is made of the temperature measurement accuracy attainable in the range 290 to 1050 K, using broadband CARS. Accuracies of 1 - 2% are attained, and laser cross coherence effects are found to be important. The determination of temperature probability density functions is of great importance to combustion science. Their measurement using single shot CARS requires the analysis of very large numbers of spectra. A study is made of fast methods of data analysis and the temperature measurement precision attainable using them. A very rapid data analysis method suitable for use in fluctuating temperature, pressure and concentration environments is developed. The temperature precision attainable using CARS is limited by CARS signal noise. For systems with high temperature fluctuations, detector counting statistics are found to make a dominant contribution to this. The spread in measured temperature probability density function width due to signal noise is characterised for the CARS system used, as a function of CARS signal strength for the temperature range 290 to 1050 K. A fast CARS signal analysis method is applied to map temperatures and temperature fluctuations in the flame zone of a turbulent oil spray furnace. The temperature measurements are compared with Discrete Droplet and Continuous Droplet oil spray model predictions (Stopford, 1984) with good agreement, particularly in the former case. In the post flame region, where turbulent fluctuations are less severe, averaged measurements of H[2]O concentrations were made.
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Liebel, Matz. "Understanding molecular dynamics with coherent vibrational spectroscopy in the time-domain." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:e0289d80-f6e3-4e6f-817e-f8dd55d15bc4.
Full textAbstract:
This thesis describes the development of several spectroscopic methods based on impulsive vibrational spectroscopy as well as of the technique itself. The first chapter describes the ultrafast time domain Raman spectrometer including the development of two noncollinear optical parametric amplifiers for sub-10 fs pulse generation with 343 or 515 nm pumping. In the first spectroscopic study we demonstrate, for the first time, that impulsive vibrational spectroscopy can be used for recording transient Raman spectra of molecules in excited electronic states. We obtain spectra of beta-carotene with comparable, or better, quality than established frequency domain based nonlinear Raman techniques. The following two chapters address the questions on the fate of vibrational coherences when generated on a reactive potential energy surface. We photoexcite bacteriorhodopsin and observe anharmonic coupling mediated vibrational coherence transfer to initially silent vibrational modes. Additionally, we are able to correlate the vibrational coherence activation with the efficiency of the isomerisation reaction in bR. Upon generation of vibrational coherence in the second excited electronic state of beta-carotene, by excitation from the ground electronic state, we are able to follow the wavepacket motion out of the Franck-Condon region. We observe vibrationally coherent internal conversion, through a conical intersection, into the first excited electronic state and are hence able to demonstrate that electronic surface crossings can occur in a vibrationally coherent fashion. Additionally, we find strong evidence for vibronic coupling mediated back and forth crossing between the two electronic states. As a combination of this work we develop a IVS based technique that allows for the direct recording of background and baseline free Raman spectra in the time domain. Several proof of principle experiments highlight the capabilities of this technique for time resolved Raman spectroscopy. In the final chapter we present work on weak-field coherent control. Here, we address the question of whether a photochemical reaction can be controlled by the phase term of an electric excitation field, in the one photon excitation limit. We study the systems rhodamine 101, bacteriorhodopsin, rhodopsin and isorhodopsin and, contrary to previous reports, find no evidence for one photon control.
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Smith, Lowenna. "Magneto-optical spectroscopy and coherent Raman studies of dilute magnetic semiconductors." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439273.
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Tenorio-Pearl, Jaime Oscar. "Coherent control of a trapped electron in a disordered dielectric." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708428.
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Xu, Xiaoji. "New methods of coherent anti-Stokes Raman spectroscopy based on broadband pulses." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/8445.
Full textAbstract:
The research work of this Ph.D. thesis is centered on coherent anti-Stokes Raman spectroscopy (CARS) with broad band coherent pulses. After a mathematical derivation of the formula that is responsible for CARS, four new approaches were proposed. The first method of Noise-autocorrelation spectroscopy with coherent Raman scattering utilizes spectral noise to reveal vibrational level spacings through autocorrelation. Its variation of Narrowband spectroscopy by all-optical correlation of broadband pulses, uses the technique of optical processing based on noisy probe pulse of special shape to obtain high resolution CARS spectra. The method of complete characterization of molecular vibration, can measure the phase of laser induced vibration through amplitude and phase retrieval on a time-frequency spectrogram. It is also a high resolution method. The final method Background free coherent Raman spectroscopy by detecting spectral phase of molecular vibrations is the spectroscopic application of detected spectral phase of laser induced vibration.
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Lee, Martin. "Imaging intra-cellular wear debris with coherent anti-Stokes Raman scattering spectroscopy." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7735.
Full textAbstract:
Aseptic loosening of artificial joints is caused by an osteolytic reaction to wear debris mediated by macrophages and other cells. Imaging these wear particles within cells can be a key process in understanding particle-cell interactions. However, the compounds used in surgical implants are not easily visualised as no tagging molecule can be added without altering the properties of the material. We were interested in using a label free optical technique known as coherent anti-Stokes Raman scattering spectroscopy (CARS) to image these particles in cells. In this thesis we studied how to use CARS to image physiologically relevant wear particles within cells. We characterised the responses from our CARS system and found them to be in good agreement to the Raman spectra we obtained for the same materials. We showed that the forward scattered CARS signal was consistently larger than the backwards scattered signal for the same size particles, and also generated a larger contrast, especially between sub-micron sized particles and the non-resonant background. Wear particles of polyethylene isolated from a pin-on-plate wear simulator were shown to be in a similar size range to those retrieved from revision tissue. When incubated in our model macrophage cells we were able to image areas of CARS signal that indicated the location of these particles in the cell. Furthermore, using multiple CARS images taken at different Raman resonances we were able to distinguish between three different polymeric compounds added to cells, showing the specificity of the technique. The inherent 3D sectioning capabilities of multiphoton microscopy were used to generate projected images of the cells and contents, as well as estimating the particle loads within cells. These results show that CARS could be an important tool in imaging intra-cellular polyethylene and characterising the interactions of wear particles with cells and the surrounding tissue.
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Barlow, Aaron M. "Spectral Distortions & Enhancements In Coherent Anti-Stokes Raman Scattering Hyperspectroscopy." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32388.
Full textAbstract:
Coherent anti-Stokes Raman scattering microscopy is a versatile technique for label-free imaging and spectroscopy of systems of biophysical interest. Due to the coherent nature of the generated signals, CARS images and spectra can often be difficult to interpret. In this thesis, we document how distortions and enhancements can be produced in CARS hyperspectroscopy as a result of the instrument, geometrical optical effects, or unique molecular states, and discuss how these effects may be suppressed or exploited in various CARS applications.
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Camp, Charles Henry Jr. "Label-free flow cytometry using multiplex coherent anti-Stokes Raman scattering (MCARS) spectroscopy." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42733.
Full textAbstract:
Over the last 50 years, flow cytometry has evolved from a modest cell counter into an invaluable analytical tool that measures an ever-expanding variety of phenotypes. Flow cytometers interrogate passing samples with laser light and measure the elastically scattered photons to ascertain information about sample size, granularity, and basic morphology. Obtaining molecular information, however, requires the addition of exogenous fluorescent labels. These labels, although a power tool, have numerous challenges and limitations such as large emission spectra and cellular toxicity. To move beyond fluorescent labels in microscopy, a variety of techniques that probe the intrinsic Raman vibrations within a sample have been developed, such as coherent anti-Stokes Raman scattering (CARS) and Raman microspectroscopy. In this dissertation, I present the first development of a label-free flow cytometer that measures the elastically scattered photons and probes the intrinsic Raman vibrations of passing
samples using multiplex coherent anti-Stokes Raman scattering (MCARS). MCARS, a coherent Raman technique that probes a large region of the Raman spectrum simultaneously, provides rich molecularly-sensitive information. Furthermore, I present its application to sorting polymer microparticles and its use in two example biological applications: monitoring lipid bodies within cultures of Saccharomyces cerevisiae, a model yeast with numerous human homologs, and monitoring the affect of nitrogen starvation on Phaeodactylum tricornutum, a diatom, which is being genetically engineered to efficiently produce biofuels.
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Gause, Oliver [Verfasser]. "Femtosecond spectroscopy and coherent control on flavins in the gas phase / Oliver Gause." Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1027151558/34.
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Gierakowski, Lays Rezende Valim. "Coherent multidimensional infrared spectroscopy : application to the study of biomolecules under oxidative stress." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/62631.
Full textAbstract:
There is a growing body of evidence which suggests post-translational modifications occurring under oxidative stress (oxPTMs) play an important role in both human health and disease. The focus of the work described in this thesis has been on the use of coherent multidimensional spectroscopy (CMDS) to perform detection and quantification of oxPTMs in a label-free and non-destructive manner. Electron-Vibration-Vibration (EVV) two-dimensional infrared (2DIR) spectroscopy is a CMDS technique which is able to directly observe intra- and intermolecular interactions. As a result, EVV 2DIR spectroscopy is particularly useful for characterising (oxPTMs). EVV 2DIR spectroscopy employs one near-IR and two mid-IR picosecond excitation beams to probe vibrational couplings in a sample via a four-wave mixing process. This results in the spread of vibrational coupling information across two dimensions, which leads to spectral decongestion and the ability to directly analyse vibrational modes within complex molecules, such as proteins. Here, tyrosine (Tyr) nitration is used as a study model due to its importance in inflammatory diseases, amongst other pathologies. Results are presented for various nitration models and will demonstrate EVV 2DIR spectroscopy's ability to identify, relatively quantify and characterise the effect of nitration of tyrosine side-chains.
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Vaughan, Joshua Charles. "Two-dimensional ultrafast pulse shaping and its application to coherent control and spectroscopy." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32492.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Vita.
Includes bibliographical references (p. 167-182).
This thesis develops powerful new methods for shaping femtosecond laser pulses in two dimensions and explores their application to coherent control of propagating lattice excitations and degenerate four-wave mixing spectroscopy. Pulse shaping in two dimensions is achieved by manipulating the spectral components of ultrashort laser pulses within many horizontal slices of the pulse. Each horizontal slice is independently shaped by means of a two-dimensional liquid crystal spatial light modulator, and taken together the shaped regions form sophisticated optical waveforms with time-dependent spatial profiles. Automated optical control over coherent lattice responses that are both time- and position-dependent across macroscopic length scales is demonstrated. Two- dimensional (2D) femtosecond pulse shaping was used to generate excitation light fields that were directed toward distinct regions of crystalline samples, producing terahertz-frequency lattice vibrational waves that emanated outward from their multiple origins at lightlike speeds. Interferences among the waves resulted in fully specified far-field responses, including tilted, focusing, or amplified wavefronts. Generation and coherent amplification of terahertz travelling waves and terahertz phased-array generation are also demonstrated. A novel approach to coherent nonlinear optical spectroscopy based on 2D femtosecond pulse shaping is introduced. Multiple phase-stable output beams are created and overlapped at the sample in a phase-matched boxcars geometry via 2D femtosecond pulse shaping.
(cont.) The pulse timing, shape, phase, and spectral content within all beams may be specified, yielding an unprecedented level of control over the interacting fields in nonlinear spectroscopic experiments. Heterodyne detection and phase cycling of the nonlinear signal is easily implemented due to the excellent phase stability between each output beam. This approach combines the waveform generation capabilities of magnetic resonance spectroscopy with the wavevector specification and phase-matching of nonlinear optical spectroscopy, yielding the signal selectivity and control capabilities of both. Results on three prototype systems will be used to illustrate the exciting possibilities with this method.
by Joshua Charles Vaughan.
Ph.D.
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Michan, Juan Mario. "Implementation of a coherent Lyman-alpha source for laser cooling and spectroscopy of antihydrogen." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46605.
Full textAbstract:
This dissertation describes two related projects: the development of a coherent Lyman-α source and the implementation of a supersonic hydrogen beam.
A two-photon resonance-enhanced four wave mixing process in krypton is used to generate high power coherent radiation at ωLy_α ⇒ 121.56 nm, the hydrogen Lyman-α line, to perform spectroscopy and cooling of magnetically trapped antihydrogen (1s − 2p transition). This is a tool to directly test both the Einstein Equivalence Principle and Charge, Parity, and Time inversion symmetry. The former can be tested by measuring the gravity interaction of matter and antimatter. Inversion symmetry can be tested by comparing the spectroscopic properties of hydrogen and antihydrogen. Both experiments require optically cooled antihydrogen. Under the current trapping conditions, optical cooling could be performed with nanosecond long pulses of 0.1 μJ of Lyman-α radiation at a repetition rate of 10 Hz.
The process to generate Lyman-α radiation uses two wavelengths (ωR ⇒ 202.31 nm and ωT ⇒ 602.56 nm), which are mixed in a sum-difference scheme (ωLy_α = 2ωR−ωT ) with a two-photon resonance at (4s²4p⁵5p[1/2]₀ ← 4s²4p⁶(¹S₀) ). The source implemented produces 1.2 μW at the Lyman-α line and this was confirmed by performing spectroscopy of hydrogen. The design, implementation and characterization of the source are discussed in this dissertation.
In the second part of the dissertation the implementation of the hydrogen beam and its characterization are discussed. The atomic hydrogen is generated with a thermal effusive source and it is entrained by an expanding noble gas. This process generates a cold beam of hydrogen atoms. Hydrogen is separated from the noble gas with a Zeeman bender that uses the forces generated by the Zeeman shift of low field seeking states of hydrogen and engineered magnetic field gradients. The hydrogen beam was characterized with a quadrupole mass spectrometer. The seed noble gas beam was characterized by colliding it with ultra-cold rubidium atoms in a magneto-optical trap. The trapped atoms loss rate resulting from these collisions can be used to measure the density of the atomic beam. This measurement demonstrates the potential of using magneto-optical traps as absolute flux monitors.
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Khalil, Munira 1975. "A tale of coupled vibrations in solution told by coherent two-dimensional infrared spectroscopy." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16607.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.Vita.
Includes bibliographical references.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Coherent two-dimensional infrared (2D IR) spectroscopy is used as a tool for investigating the molecular structure and dynamics of coupled vibrations in solution on a picosecond timescale. The strongly coupled asymmetric and symmetric carbonyl stretches of Rh(CO)₂C₅H₇0₂ (RDC) dissolved in hexane serve as a convenient model system. Fourier transform 2D IR spectra are obtained from heterodyne-detected third-order nonlinear signals using a sequence of broad bandwidth femtosecond IR pulses. A 2D IR correlation spectrum with absorptive lineshapes results from the addition of 2D rephasing and non-rephasing spectra, which sample conjugate frequencies in the evolution time period. The 2D IR correlation spectrum contains peaks with different positions, signs, amplitudes and lineshapes. The positions of the peaks map the transition frequencies between the ground, singly, and doubly excited states of the system, and thus describe the anharmonic vibrational potential. Peak amplitudes reflect the relative magnitudes and orientations of the transition dipole moments in the molecular frame, the electrical anharmonicity of the system, and the vibrational relaxation dynamics. The 2D line shapes are sensitive to the complicated system-bath interactions in solution. 2D IR spectra taken with varying polarization conditions and as a function of a variable waiting time can be used to isolate and quantify these spectroscopic observables. The polarization-selective 2D IR spectra of RDC in hexane are analyzed in terms of two coupled local coordinates to obtain their mutual orientation and the magnitude of the coupling between them. Evidence of vibrational coherence transfer between close-lying transition frequencies is indicated by the presence of extra induced peaks in 2D IR
(cont.) rephasing spectra. The data is modeled by using Redfield theory to account for coherence transfer, vibrational dephasing and population relaxation in a multilevel vibrational system. Building on the studies of the RDC model system, 2D IR spectroscopy is used to study the thermal denaturation of RNase A by characterizing the temperature-dependent Amide I band. A nonlinear IR probe is used to study the early events in the laser temperature-jump initiated denaturation of RNase A.
by Munira Khalil.
Ph.D.
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Stone, Katherine Walowicz. "Coherent multi-exciton dynamics in semiconductor nanostructures via two-dimensional Fourier transform optical spectroscopy." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49554.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 139-149).
The Coulomb correlations between photoexcited charged particles in materials such as photosynthetic complexes, conjugated polymer systems, J-aggregates, and bulk or nanostructured semiconductors produce a hierarchy of collective electronic excitations (i.e. excitons, biexcitons, etc.) which may be harnessed for applications in quantum optics, light-harvesting, or quantum information technologies. These excitations represent correlations among successively greater numbers of electrons and holes, and their associated multiple-quantum coherences could reveal detailed information about complex many-body interactions and dynamics. However, unlike single-quantum coherences involving excitons, multiple-quantum coherences do not radiate and they have largely eluded direct observation and characterization. In this work, I present a novel optical technique, two-quantum two-dimensional Fourier transform optical spectroscopy, which allows direct observation of the dynamics of multiple-exciton states that reflect the correlations of their constituent electrons and holes. The approach is based on closely analogous methods in nuclear magnetic resonance, in which multiple phase-coherent fields are used to drive successive transitions such that multiple-quantum coherences can be accessed and probed. A spatiotemporal femtosecond pulse shaping technique has been used to overcome the challenge of control over multiple, noncollinear phase-coherent optical Fields in the experimental geometries that are used to isolate selected signal contributions through wavevector matching.
(cont.) Results from a GaAs quantum well system reveal distinct coherences of biexcitons that are formed from two identical excitons or from two excitons whose holes are in di®erent spin sublevels ("heavy-hole" and "light-hole" excitons). The biexciton binding energies and dephasing dynamics are determined, and changes in the dephasing rates as a function of the excitation density are observed, revealing still higher-order correlations due to exciton-biexciton interactions. Two-quantum coherences due to four-particle correlations that do not involve bound biexciton states but that in°uence the exciton properties are also observed and characterized. I also present one-quantum two-dimensional Fourier transform optical spectroscopy measurements which show that the higher-order correlations isolated by two-quantum techniques are highly convolved with two-particle correlations in the conventional one-quantum measurements.
by Katherine Walowicz Stone.
Ph.D.
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Upadhya, Prasanth Chandrashekara. "Coherent generation and detection of Terahertz radiation : time domain Terahertz spectroscopy of molecular crystals." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614771.
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Tumino, Biagio. "Growth and coherent spectroscopy of europium- and praseodymium-doped crystals for quantum memory applications." Paris 6, 2013. http://www.theses.fr/2013PA066188.
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Les solides dopés par des ions de terre rare sont des candidats prometteurs pour des applications en information quantique. En particulier, le cristal Eu3+:Y2SiO5 possède des propriétés de cohérence et une structure de niveaux d’énergie qui le rendent adapté pour la réalisation de mémoires quantiques. Avec le support du projet européen QuRep, ce travail détaille les mesures spectroscopiques réalisées pour determiner les conditions optimales (en termes de préparation du matériau ou de concentration du dopant) pour obtenir des mémoires quantiques performantes. Pour cela, deux méthodes de croissance différentes (Czochralski et à fusion de zone) ont été utiliées et les conditions de croissance optimisées. La transition optique de l’europium 7F0 – 5D0 a été étudiée avec des techniques de spectroscopie à haute résolution pour caractériser les différents matériaux en termes de pic d’absorption, de largeur inhomogène et de temps de cohérence optique. La strucuture hyperfine des deux isotopes de l’europium (151Eu and 153Eu) a été aussi caractérisée en appliquant un champ magnétique externe. Des mesures Diffusion Raman Cohérente ont permis de déterminer le temps de cohérence des niveaux hyperfins de l’état de base dans 151/153Eu3+:Y2SiO5 (entre 10 et 20 ms) à champ nulRare-earth-doped solids are promising materials as light-matter interfaces for quantum applications. In particular, europium-doped yttrium orthosilicate crystal (Eu3+:Y2SiO5) shows coherence properties and a ground-state energy-level structure suitable for quantum memory applications. Within the european project QuRep, spectroscopic investigations of this material are reported in order to determine the optimal conditions (in terms of material’s purity or ions concentration) for obtaining high performance quantum memories. Two crystal growth techniques (Czochralski and melting zone) are also used in order to refine the growth conditions for this material. The europium optical transition 7F0 – 5D0 is investigated by high resolution-absorption and photon echo techniques in order to study the absorption coefficient peak, the inhomogeneous linewidth and the optical coherence lifetime as function of different conditions. The hyperfine structure of the two europium isotopes (151Eu and 153Eu) is also analyzed by applying an external static magnetic field. Coherent Raman Scattering measurements are performed in order to measure the hyperfine coherence lifetime in 151/153Eu3+:Y2SiO5 found to be in the range of 10-20 ms at zero magnetic field
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Hung, Yi-chen Hung. "Characterization of Nonequilibrium Reacting Molecular Plasmas and Flames using Coherent Anti-Stokes Raman Spectroscopy." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531930166735281.
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Paul, Jagannath. "Coherent Response of Two Dimensional Electron Gas probed by Two Dimensional Fourier Transform Spectroscopy." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6738.
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Advent of ultrashort lasers made it possible to probe various scattering phenomena in materials that occur in a time scale on the order of few femtoseconds to several tens of picoseconds. Nonlinear optical spectroscopy techniques, such as pump-probe, transient four wave mixing (TFWM), etc., are very common to study the carrier dynamics in various material systems. In time domain, the transient FWM uses several ultrashort pulses separated by time delays to obtain the information of dephasing and population relaxation times, which are very important parameters that govern the carrier dynamics of materials. A recently developed multidimensional nonlinear optical spectroscopy is an enhanced version of TFWM which keeps track of two time delays simultaneously and correlate them in the frequency domain with the aid of Fourier transform in a two dimensional map. Using this technique, the nonlinear complex signal field is characterized both in amplitude and phase. Furthermore, this technique allows us to identify the coupling between resonances which are rather difficult to interpret from time domain measurements. This work focuses on the study of the coherent response of a two dimensional electron gas formed in a modulation doped GaAs/AlGaAs quantum well both at zero and at high magnetic fields.
In modulation doped quantum wells, the excitons are formed as a result of the inter- actions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the formation of Mahan excitons, which is also referred to as Fermi edge singularity (FES). Polarization and temperature dependent rephasing 2DFT spectra in combination with TI-FWM measurements, provides insight into the dephasing mechanism of the heavy hole (HH) Mahan exciton. In addition to that strong quantum coherence between the HH and LH Mahan excitons is observed, which is rather surprising at this high doping concentration. The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence be destroyed as a result of the screening and electron-electron interactions. Such correlations are revealed by the dominating cross-diagonal peaks in both one-quantum and two-quantum 2DFT spectra. Theoretical simulations based on the optical Bloch Equations (OBE) where many-body effects are included phenomenologically, corroborate the experimental results. Time-dependent density functional theory (TD-DFT) calculations provide insight into the underlying physics and attribute the observed strong quantum coherence to a significantly reduced screening length and collective excitations of the many-electron system. Furthermore, in semiconductors under the application of magnetic field, the energy states in conduction and valence bands become quantized and Landau levels are formed. We observe optical excitation originating from different Landau levels in the absorption spectra in an undoped and a modulation doped quantum wells. 2DFT measurements in magnetic field up to 25 Tesla have been performed and the spectra reveal distinct difference in the line shapes in the two samples. In addition, strong coherent coupling between landau levels is observed in the undoped sample. In order to gain deeper understanding of the observations, the experimental results are further supported with TD-DFT calculation.
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Wijekoon, Wijekoon Mudiyanselage Kapila Piyasena. "Waveguide Surface Coherent anti-Stokes Raman Scattering Spectroscopy and optical second harmonic generation spectroscopy of molecules adsorbed on metal oxide surfaces." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184444.
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This dissertation reports the application of nonlinear optical effects for the investigation of vibrational and electronic spectroscopy of molecules adsorbed on thin film metal oxide surfaces and metal oxide surfaces. The main emphasis of the experiments cited here is to introduce the recently developed multi-photon technique, Waveguide Surface Coherent anti-Stokes Raman Scattering Spectroscopy (WSCARS), to the scientific community. Planar optical waveguides have been utilized to generate large optical field enhancements on metal oxide surfaces. Guided waves have been employed to obtain the surface coherent anti-Stokes Raman scattering spectra of pyridine, phenol, benzene, methanol, CD₃OD, 2,4-pentadione, oxygen, ammonia and ND₃ adsorbed onto a ZnO (0001) surface. Vibrational spectra of transient species (O₂⁻) adsorbed on ZnO (0001) surface are also presented. Furthermore, the WSCARS has been used to monitor catalytic hydrogenation of ethylene adsorbed on ZnO (0001) surface. The WSCARS technique is compared with the other vibrational surface probes. Future directions and limitations of the technique are also discussed. Electronic spectra of surface bound species have been examined by resonantly enhanced surface second harmonic generation (SSHG). SHG spectra of trans-cinnamic acid adsorbed on optically cleaned fused silica have been obtained at room temperature and at 4 K. Surface second harmonic generation has been applied to study the adsorption of water and acetone onto thermally grown silicon dioxide/silicon surface. SSHG has been successfully applied to monitor photo-oxidation and photo-reduction of a rutile (110) surface. Experiments are described, data are presented, and surface-adsorbate binding modes are discussed.
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Feng, Zhenxing 1982. "Experimental and theoretical investigation of the coherent x-ray propagation and diffraction." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101122.
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Coherent X-ray diffraction and X-ray Intensity Fluctuation Spectroscopy (XIFS) are ideal methods and techniques to perform measurements on the dynamics of fluctuations in condensed matter materials. To investigate more systems and faster fluctuations by being able to tune the coherence length, we use a zone plate to change the coherence length and beam size but keep most of the intensity. Using the zone plate, experiments were carried out to measure the properties of the focused beam. We applied a formalism to calculate the effect of optics on coherence. We tested our results by doing measurement at Advanced Photon Source. We measured the focal properties of the zone plate, speckle sizes and contrast, obtained by using coherent X-ray diffraction from an disordered Fe3Al crystals. Our theoretical calculations are compared with the experimental results.
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Hogben, Hannah J. "Coherent spin dynamics of radical pairs in weak magnetic fields." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:61c4ab7e-406f-4193-949a-b5a70f43e3e1.
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The outcome of chemical reactions proceeding via radical pair (RP) intermediates can be influenced by the magnitude and direction of applied magnetic fields, even for interaction strengths far smaller than the thermal energy. Sensitivity to Earth-strength magnetic fields has been suggested as a biophysical mechanism of animal magnetoreception and this thesis is concerned with simulations of the effects of such weak magnetic fields on RP reaction yields. State-space restriction techniques previously used in the simulation of NMR spectra are here applied to RPs. Methods for improving the efficiency of Liouville-space spin dynamics calculations are presented along with a procedure to form operators directly into a reduced state-space. These are implemented in the spin dynamics software Spinach. Entanglement is shown to be a crucial ingredient for the observation of a low field effect on RP reaction yields in some cases. It is also observed that many chemically plausible initial states possess an inherent directionality which may be a useful source of anisotropy in RP reactions. The nature of the radical species involved in magnetoreception is investigated theoretically. It has been shown that European Robins are disorientated by weak radio-frequency (RF) fields at the frequency corresponding to the Zeeman splitting of a free electron. The potential role of superoxide and dioxygen is investigated and the anisotropic reaction yield in the presence of a RF-field, without a static field, is calculated. Magnetic field effect data for Escherichia coli photolyase and Arabidopsis thaliana cryptochrome 1, both expected to be magnetically sensitive, are satisfactorily modelled only when singlet-triplet dephasing is included. With a view to increasing the reaction yield anisotropy of a RP magnetoreceptor, a brief study of the amplification of the magnetic field experienced by a RP from nearby magnetite particles is presented. Finally in a digression from RPs, Spinach is used to determine the states expected to be immune from relaxation and therefore long-lived in NMR experiments on multi-spin systems.
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Atherton, Kathryn Jane. "Coherent Raman studies of optical nonlinearities in conjugated molecules and polymers." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298790.
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Binz, Marcel [Verfasser], and Frank [Akademischer Betreuer] Stienkemeier. "Phase-modulated coherent spectroscopy of rubidium: High-intensity effects and the interaction with helium nanodroplets." Freiburg : Universität, 2021. http://d-nb.info/1235325806/34.
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Hensen, Matthias [Verfasser]. "Concentrating Light: Nano-devices for spectroscopy, ultra-fast current injection and coherent energy transport / Matthias Hensen." Bielefeld : Universitätsbibliothek Bielefeld, 2016. http://d-nb.info/1105645533/34.
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Dey, Prasenjit. "Exciton Dynamics and Many Body Interactions in Layered Semiconducting Materials Revealed with Non-linear Coherent Spectroscopy." Thesis, University of South Florida, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10076073.
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Atomically thin, semiconducting transition metal dichalogenides (TMDs), a special class of layered semiconductors, that can be shaped as a perfect two dimensional material, have garnered a lot of attention owing to their fascinating electronic properties which are achievable at the extreme nanoscale. In contrast to graphene, the most celebrated two-dimensional (2D) material thus far; TMDs exhibit a direct band gap in the monolayer regime. The presence of a non-zero bandgap along with the broken inversion symmetry in the monolayer limit brands semiconducting TMDs as the perfect candidate for future optoelectronic and valleytronics-based device application. These remarkable discoveries demand exploration of different materials that possess similar properties alike TMDs. Recently, III-VI layered semiconducting materials (example: InSe, GaSe etc.) have also emerged as potential materials for optical device based applications as, similar to TMDs, they can be shaped into a perfect two-dimensional form as well as possess a sizable band gap in their nano-regime. The perfect 2D character in layered materials cause enhancement of strong Coulomb interaction. As a result, excitons, a coulomb bound quasiparticle made of electron-hole pair, dominate the optical properties near the bandgap. The basis of development for future optoelectronic-based devices requires accurate characterization of the essential properties of excitons. Two fundamental parameters that characterize the quantum dynamics of excitons are: a) the dephasing rate, γ, which represents the coherence loss due to the interaction of the excitons with their environment (for example- phonons, impurities, other excitons, etc.) and b) excited state population decay rate arising from radiative and non-radiative relaxation processes. The dephasing rate is representative of the time scale over which excitons can be coherently manipulated, therefore accurately probing the source of exciton decoherence is crucial for understanding the basic unexplored science as well as creating technological developments. The dephasing dynamics in semiconductors typically occur in the picosecond to femtosecond timescale, thus the use of ultrafast laser spectroscopy is a potential route to probe such excitonic responses.
The focus of this dissertation is two-fold: firstly, to develop the necessary instrumentation to accurately probe the aforementioned parameters and secondly, to explore the quantum dynamics and the underlying many-body interactions in different layered semiconducting materials. A custom-built multidimensional optical non-linear spectrometer was developed in order to perform two-dimensional spectroscopic (2DFT) measurements. The advantages of this technique are multifaceted compared to regular one-dimensional and non-linear incoherent techniques. 2DFT technique is based on an enhanced version of Four wave mixing experiments. This powerful tool is capable of identifying the resonant coupling, probing the coherent pathways, unambiguously extracting the homogeneous linewidth in the presence of inhomogeneity and decomposing a complex spectra into real and imaginary parts. It is not possible to uncover such crucial features by employing one dimensional non-linear technique.
Monolayers as well as bulk TMDs and group III-VI bulk layered materials are explored in this dissertation. The exciton quantum dynamics is explored with three pulse four-wave mixing whereas the phase sensitive measurements are obtained by employing two-dimensional Fourier transform spectroscopy. Temperature and excitation density dependent 2DFT experiments unfold the information associated with the many-body interactions in the layered semiconducting samples.
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Simon, Russell James. "The use of Coherent Anti-Stokes Raman Spectroscopy as a diagnostic technique for studying the hydrogenation of carbon moxide {i.e. monoxide} in a tube-wall reactor." Thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/23441.
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Karthik, G. "Investigations Of Spin-Dynamics And Steady-States Under Coherent And Relaxation Processes In Nuclear Magnetic Resonance Spectroscopy." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/259.
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The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle. The atomic nucleus is comprised of the protons and the neutrons which possess a spin each. The composite object- the atomic nucleus is therefore a tiny magnet itself. In the presence of an external bias like a magnetic field, the nucleus therefore evolves like a magnetic moment and attains a characteristic frequency in its evolution called the Larmor frequency given by,
(formula)
where η is the magnetogyric ratio of the particle and B is the applied magnetic field. The existence of a natural frequency presents the possibility of a resonance behaviour in the response of the system when probed with a driving field. This is the basic principle of magnetic resonance, which in the context of the atomic nucleus, was discovered independently by Purcell [2] and Bloch [3].
From its conception, the technique and the associated understanding of the involved phenomena have come a long way. In its original form the technique involved the study of the steady-state response of the nuclear magnetic moment to a driving field. This continuous wave NMR had the basic limitation of exciting resonances in a given sample, serially. In due course of time, this technique was replaced by the Fourier transform NMR (FTNMR) [4]. This technique differed from the continuous wave NMR in its study of the transient response of the system in contrast to the steady-state response in the former. The advantage of this method is the parallel observation of all the resonances present in the system ( within the band-width of the excitation). In addition to the bias created by the external field, other internal molecular fields produce additional bias which in turn produce interesting signatures on the spectrum of the system, which are potential carriers of information about the molecular state. The fact that the spins are not isolated from the molecular environment, produces a striking effect on the ideal spectrum of the system. These effects contain in them, the signatures of the molecular local environment and are hence of immense interest to physicists, chemists and biologists.