Dissertations / Theses on the topic 'Optical spectroscopy'
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Chao, Karl 1960. "Modulated emittance spectroscopy." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/276977.
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The electronic bandstructure of solids near room temperature has been successfully explored with previous versions of modulation spectroscopy. Modulation of parameters which enter into the bandstructure produce a dielectric function variation. This changes the optical observables, such as reflectance or absorptance. Modulation resonances are observed near singularities in the joint density-of-states function. These resonances must also be detectable in the emittance, an observable which also depends on the dielectric function. Thus, this work investigates the possibility of detection of optical resonances riding on the temperature derivative of the blackbody emission from a solid at high temperature. The modulated emittance was separated from the thermal background by a detection scheme utilizing a CCD and computer. The resonances were not observed because of excessive CCD noise. The existance and magnitude of the resonances was based upon results from other modulation spectroscopies.
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Hamer, Peter John. "Optical spectroscopy of conjugated polymers." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/265460.
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I have conducted studies of the optical properties of two model conjugated systems (poly-(p-phenylenevinylene) and a set of zinc-centred oligo-(porphyrins) ). Various optical probing techniques have been employed to study the nature and behaviour of the primary photoexcited state of poly-(p-phenylenevinylene) (PPV) and photogenerated charged states within the porphyrins. Implantation of PPV films by high energy (30ke V) ions has been employed to introduce controlled damage into the film. Subsequently, studies of the absorption, fluorescence, photo-induced absorption and photocurrent response of the treated films has been used to model the behaviour of the photogenerated exciton after excitation. At the same time, the . probing sheds light on the mechanisms at work in the deceleration of the implanted ions and the nature and location of the damage produced. A study of the effect of applied electrical field on the fluorescence of PPV is analysed in terms of existing models of exciton dissociation. The results support the view of the primary photo-excitation as a self-localised exciton with a binding energy of some tenths of an electron volt and a spatial extent of a few nanometers. Measurements of the effect of current flow in the device extend the study of exciton diffusion started in the study of ion implanted PPV. Measurements of persistent fluorescence quenching subsequent to current flow in the material suggest that charge accumulation may be a serious limiting factor in the performance of polymer light-emitting diodes. Studies of the absorption, fluorescence and photo-induced absorption of a set of novel conjugated oligomers based on a zinc-centred porphyrin, show that the optical properties are strongly influenced by charged states generated from the dissociation of the primary photoexcitation. Such charged states are found to have lifetimes of some milliseconds even at room temperature.
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Berry, Andrew John. "Optical spectroscopy of terbium elpasolites." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320164.
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Fox, A. M. "Nonlinear optical spectroscopy of semiconductors." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379992.
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Bowmar, Paul. "Optical spectroscopy of novel materials." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259758.
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Seward, Harriet Elizabeth Thurza. "Magneto-optical spectroscopy of hemoproteins." Thesis, University of East Anglia, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323295.
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Turner, R. J. "Optical spectroscopy of magnetic insulators." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374810.
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Sobiesierski, Z. "Optical spectroscopy of disordered systems." Thesis, University of Exeter, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374944.
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Hartschuh, Ryan D. "Optical Spectroscopy of Nanostructured Materials." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195016254.
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Trefiak, Nicholas Ronald. "Ringdown spectroscopy in optical waveguides." Thesis, Kingston, Ont. : [s.n.], 2007. http://hdl.handle.net/1974/436.
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Murdin, Benedict Neil. "Magneto-optical and non-linear optical spectroscopy of semiconductors." Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1450.
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Patil, Raj. "Deep UV Raman Spectroscopy." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/613378.
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This thesis examines the performance of a custom built deep UV laser (257.5nm) for Raman spectroscopy and the advantages of Raman spectroscopy with a laser in the deep UV over a laser in the visible range (532 nm). It describes the theory of resonance Raman scattering, the experimental setup for Raman spectroscopy and a few Raman spectroscopy measurements. The measurements were performed on biological samples oak tree leaf and lactobacillus acidophilus and bifidobacteria from probotioc medicinal capsules. Fluorescence free Raman spectra were acquired for the two samples with 257.5 nm laser. The Raman spectra for the two samples with a 532nm laser was masked with fluorescence. Raman measurements for an inorganic salt sodium nitrate showed a resonance Raman effect with 257.5 nm laser which led to enhancement in the Raman intensity as compared to that with 532 nm laser. Therefore we were able to demonstrate two advantages of deep UV Raman spectroscopy. First one is the possibility of acquiring fluorescence free spectra for biological samples. Second is the possibility of gaining enhancement in Raman intensity due to resonance Raman effect. It was observed that 257.5 nm laser requires optimization to reduce the bandwidth of the laser to get better resolution. The 257.5 nm laser also needs to be optimized to obtain higher power to get better signal to noise ratio. The experimental setup can also be further improved to obtain better resolution. If the improvements required in the setup are implemented, the deep UV Raman setup will become an important tool for spectroscopy.
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Larsson, Arvid. "Optical spectroscopy of InGaAs quantum dots." Doctoral thesis, Linköpings universitet, Halvledarmaterial, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-64707.
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The work presented in this thesis deals with optical studies of semiconductor quantum dots (QDs) in the InGaAs material system. It is shown that for self-assembled InAs QDs, the interaction with the surrounding GaAs barrier and the InAs wetting layer (WL) in particular, has a very large impact on their optical properties. The ability to control the charge state of individual QDs is demonstrated and attributed to a modulation in the carrier transport dynamics in the WL. After photo-excitation of carriers (electrons and holes) in the barrier, they will migrate in the sample and with a certain probability become captured into a QD. During this migration, the carriers can be affected by exerting them to an external magnetic field or by altering the temperature. An external magnetic field applied perpendicular to the carrier transport direction will lead to a decrease in the carrier drift velocity since their trajectories are bent, and at sufficiently high field strength become circular. In turn, this decreases the probability for the carriers to reach the QD since the probability for the carriers to get trapped in WL localizing potentials increases. An elevated temperature leads to an increased escape rate out of these potentials and again increases the flow of carriers towards the QD. These effects have significantly different strengths for electrons and holes due to the large difference in their respective masses and therefore it constitutes a way to control the supply of charges to the QD. Another effect of the different capture probabilities for electrons and holes into a QD that is explored is the ability to achieve spin polarization of the neutral exciton (X0). It has been concluded frequently in the literature that X0 cannot maintain its spin without application of an external magnetic field, due to the anisotropic electron – hole exchange interaction (AEI). In our studies, we show that at certain excitation conditions, the AEI can be by-passed since an electron is captured faster than a hole into a QD. The result is that the electron will populate the QD solely for a certain time window, before the hole is captured. During this time window and at polarized excitation, which creates spin polarized carriers, the electron can polarize the QD nuclei. In this way, a nuclear magnetic field is built up with a magnitude as high as ~ 1.5 T. This field will stabilize the X0 spin in a similar manner as an external magnetic field would. The build-up time for this nuclear field was determined to be ~ 10 ms and the polarization degree achieved for X0 is ~ 60 %. In contrast to the case of X0, the AEI is naturally cancelled for the negatively charged exciton (X-) and the positively charged exciton (X+) complexes. This is due to the fact that the electron (hole) spin is paired off in case of X- (X+). Accordingly, an even higher polarization degree (~ 73 %) is measured for the positively charged exciton. In a different study, pyramidal QD structures were employed. In contrast to fabrication of self-assembled QDs, the position of QDs can be controlled in these samples as they are grown in inverted pyramids that are etched into a substrate. After sample processing, the result is free-standing AlGaAs pyramids with InGaAs QDs inside. Due to the pyramidal shape of these structures, the light extraction is considerably enhanced which opens up possibilities to study processes un-resolvable in self-assembled QDs. This has allowed studies of Auger-like shake-up processes of holes in single QDs. Normally, after radiative recombination of X+, the QD is populated with a ground state hole. However, at recombination, a fraction of the energy can be transferred to the hole so that it afterwards occupies an excited state instead. This process is detected experimentally as a red-shifted luminescence satellite peak with an intensity on the order of ~ 1/1000 of the main X+ peak intensity. The identification of the satellite peak is based on its intensity correlation with the X+ peak, photoluminescence excitation measurements and on magnetic field measurements.Arbetet som presenteras i denna avhandling rör studier av kvantprickars optiska egenskaper. En kvantprick är en halvledarkristall som endast är några tiotals nanometer stor. Den ligger oftast inbäddad inuti en större kristall av ett annat halvledarmaterial och pga. den begränsade storleken får en kvantprick mycket speciella egenskaper. Bland annat så kommer elektronerna i en kvantprick endast att kunna anta vissa diskreta energinivåer liknande situationen för elektronerna i en atom. Följaktligen kallas kvantprickar ofta för artificiella atomer. För halvledarmaterial gäller det generellt att det inte endast är fria elektroner i ledningsbandet, som kan leda ström utan även tomma elektrontillstånd i valensbandet, vilka uppträder som positivt laddade partiklar, kan leda ström. Dessa kallas kort och gott för hål. I en kvantprick har hålen såsom elektronerna helt diskreta energinivåer. Precis som är fallet i en atom, så kommer elektroniska övergångar mellan olika energinivåer i en kvantprick att resultera i att ljus emitteras. Energin (dvs. våglängden alt. färgen) för detta ljus bestäms av hur energinivåerna i kvantpricken ligger, för elektronerna och hålen, och genom att analysera ljuset kan man således studera kvantprickens egenskaper. Studierna i den här avhandlingen visar att växelverkan mellan en kvantprick och den omgivande kristallen, som den ligger inbäddad i, har stor inverkan på kvantprickens optiska egenskaper. T.ex. visas att man kan kontrollera antalet elektroner, som kommer att finnas i kvantpricken genom att modifiera hur elektronerna kan röra sig i omgivningen. Dessa rörelser modifieras här genom att variera temperaturen och genom att lägga på ett magnetiskt fält. Ett magnetiskt fält, vinkelrätt mot en elektrons rörelse, kommer att böja av dess bana och dess chans att nå fram till kvantpricken kan således minskas. Elektronen kan då istället fastna i andra potentialgropar i kvantprickens närhet. Genom att öka temperaturen, vilket ger elektronerna större energi, kan deras chans att nå fram till kvantpricken å andra sidan öka. En annan effekt, som studerats, är möjligheten att kontrollera spinnet hos elektronerna i en kvantprick. Även i dessa studier visar det sig att växelverkan med omgivningen spelar stor roll och kan användas till att kontrollera elektronens spin. Mekanismen som föreslås är att om elektronerna hinner före hålen till kvantpricken, så hinner de överföra sitt spin till atomkärnorna i kvantpricken. På detta sätt kan man få atomkärnornas spin polariserat, vilket resulterar i ett inbyggt magnetfält, i storleksordningen 1.5 Tesla, som i sin tur hjälper till att upprätthålla en hög grad av spinpolarisering även hos elektronerna. För att få elektronerna att hinna först, måste deras rörelser i omgivningen kontrolleras. I en ytterligare studie undersöktes den process där en elektronisk övergång i kvantpricken inte enbart resulterar i emission av ljus, utan även i att en annan partikel tar över en del av energin och blir exciterad. Dessa processer avspeglas i att en del av det ljus som emitteras har lägre energi. Detta ljus är också mycket svagt, ca 1000 ggr lägre intensitet, och möjligheten att kunna mäta detta är helt beroende på hur ljusstarka kvantprickarna är. De prover som använts i denna studie består av pyramidstrukturer, ca 7.5 mikrometer stora, med kvantprickar inuti. Denna geometri ger ca 1000 ggr bättre ljusutbyte jämfört med traditionella strukturer, vilket möjliggjort studien.
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Williams, Stephen J. "Optical Spectroscopy of Massive Binary Stars." Digital Archive @ GSU, 2011. http://digitalarchive.gsu.edu/phy_astr_diss/49.
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This is a spectroscopic and photometric study of suspected close binary systems among the massive stars. The stars studied here include stars with temperatures ranging from 45,000 Kelvin (K) to 15,000 K, corresponding to spectral types ranging from O3 V to B5 III, masses between 47 Solar Masses and 5 Solar Masses, and absolute V magnitudes from -6.28 to -2.0. I categorize 30 targets according to my spectroscopic observations into groups with no radial velocity variability, single-lined, and double-lined variability. My analysis of the 18 constant velocity stars results in estimates of stellar effective temperature, Teff, gravity, log g, projected rotational velocity, v sin i, and spectral classification. Analyzing single-lined systems, I find the same stellar parameters for five more systems, and also present the first orbits for these systems. I also explore the probable characteristics of the unseen companions in these systems. Three double-lined systems, two eclipsing and one with an ellipsoidal variation in the light curve, are fully analyzed, and I present important astrophysical parameters for each of these systems, including stellar masses, radii, ages, and distances to each system. The masses are accurate to 4.3% and 3.6% for the primary and secondary for LH 54-425, 2.1% and 1.6% for HI Mon, and 1.1% and 0.6% for HD 42401. Two more double-lined systems are studied, and preliminary results are presented. Photometric observations are analyzed for 56 targets from the All Sky Automated Survey in order to facilitate spectroscopic observations at key points in the binary orbit where spectral features of both components will be well separated. New spectroscopic observations of these eclipsing binaries with my computed ephemerides will allow us to obtain double-lined orbital elements and determine their masses, radii, ages, and distances. These computed parameters will then allow for comparison with theoretical stellar models, and a better understanding of the evolution of massive stars.
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Prince, Barry J. "Optical spectroscopy of porphyrin-like systems." Thesis, University of Canterbury. Chemistry, 1999. http://hdl.handle.net/10092/6100.
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This thesis presents the results of absorption, magnetic circular dichroism (MCD), selective excitation, fluorescence-detected MCD (FDMCD), total luminescence (TL), magnetic circularly polarised luminescence (MCPL) and spectral hole-burning (HB) studies of zinc porphyrin derivatives isolated in argon matrices. These spectroscopic studies have focused on the lowest-energy * transition of these molecules; the Q transition.
These studies have been driven by two main areas of interest in matrix-isolated metalloporphyrins; the degree to which intermolecular coupling occurs in such matrices, and the role of the Jahn-Teller (JT) effect in these systems.
Spectra collected mark the first examples of the application of the selective MCPL and FDMCD, the latter of which has the potential, not only to provide superior resolution over conventional MCD, but also, in some cases, to give an enhancement in S/N. The construction of a spectrometer was necessary for the collection of these spectra and comprised a significant portion of the work.
The development of a new matrix deposition technique, in conjunction with selective excitation, TL and HB studies of the Q-band of zinc phthalocyanine, has provided evidence of the existence of interacting pairs of molecules in this matrix, The population of these 'coupled-pair' sites, which absorb to the red side of the Q-band origin, increases if the matrix in annealed, and at the same time the efficiency of HB is also increased, These results also provide information regarding the mechanism of HB in these systems, which is thought to involve intermolecular triplet-state charge separation followed by singlet recombination.
Three approaches were adopted for the study of the JT effect in the Q (1Eu) states of these systems. A program (JTCFZ) was written to generate and solve the E b vibronic Hamiltonian matrix and to simulate the absorption and MCD spectra for an E A transition of a system with a single effective JT-active vibrational mode in the D4h pointgroup. Although this model provides insight into many of the observed characteristics of these systems, its inability to account for the finer details of the spectra of a number of systems points to an inadequacy of the single-mode approach.
Normal coordinate analysis was used in conjunction with a semi-empirical molecular orbital (MO) calculation to approximate the JT displacements (JT) of the Q state along all potentially JT-active modes of ZnPc. The results indicate that there are many modes with significant JT values, reinforcing the view that the effective singlemode model cannot adequately describe these systems.
This conclusion is further supported by selective FDMCD spectra of ZnPc/Ar and ZnTBP/Ar for which the sign of totally symmetric vibrational overtones is opposite to that of JT-active overtones. As predicted by the calculations, many JT-active overtones of varying intensities appear throughout the entire Q-band envelopes of these systems.
FDMCD spectra of ZnPc/Ar has also provided evidence for the assignment of a transition (Q') underlying the higher vibrational overtones of the Q band. The spectra collected clearly demonstrate that a previous assignment of this transition to 1A1u 1A1g is not correct and, with additional support from semi-emperical MO calculations, it has been reassigned as 1Eu 1A1g.
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Thomas, D. W. "Optical spectroscopy with continuous-wave lasers." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639205.
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The principles behind the production of laser beams and their important characteristics are outlined briefly in the first introductory chapter. In chapters 2 and 3, and theory is developed for the studies of the transmission and Raman scattering behaviour of aligned liquid crystal molecules with respect to laser beams of well-defined polarisations. The sample studied was a mixture of cyanobiphenyls, LCE7, and was aligned using the technique of Linear Photopolymerisation, LPP. Concentration-Modulated Absorption Spectroscopy, COMAS, a pump-probe technique is described in chapters 4 - 7. In chapter 4, the principles are described briefly for both pulsed and continuous-wave laser beams for 2-level kinetic schemes. In this thesis, the theory is developed for 3-level schemes, which allows the determination of the re-population lifetimes of species in the range ca. 10ms - 10ns, by measuring the COMAS "gain" as a function of the pump beam modulation frequency. The optical COMAS systems are described in chapter 5. The triplet lifetimes of the Xanthene dyes Rose Bengal and Eosin Y in ethanolic solutions have been measured in chapter 6 and are in general agreement with literature values. Using experimental data and the COMAS calculations it is possible to determine the absolute absorption cross-sections of the dye molecules at the probe laser wavelength. In chapter 7 the 3-level scheme has been modified to consider the re-population kinetics of Neon atoms in a hollow cathode discharge. The studies show that there exist two rates of repopulation for the lower level of the transition monitored, which give rise to two "gain" components with distinct rates of re-population ca. 2x105s-1 and 5x107s-1. It is shown that by taking into account the prominent role of saturation, it is possible to measure accurately species concentrations and absorption cross-sections.
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Huang, Fumin. "Tip-enhanced optical spectroscopy and microscopy." Thesis, King's College London (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422276.
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Vuong, Phuong. "Optical spectroscopy of boron nitride heterostructures." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS075/document.
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Le nitrure de bore hexagonal (h-BN) est un semi-conducteur à large bande interdite (~ 6 eV) avec une stabilité thermique et chimique très élevées lui offrant la possibilité d'être utilisé dans des dispositifs fonctionnant dans des conditions de fonctionnements extrêmes. La nature indirecte de la bande interdite dans h-BN a été étudiée à la fois par des calculs théoriques et par des expériences. Un exciton indirect et des recombinaisons assistées par phonons dans h-BN ont été observées par photoluminescence.Durant cette thèse, nous avons étudié les propriétés optiques de cristaux massifs et de couches hétéro-épitaxiales de nitrure de bore hexagonal. Nous avons étudié des échantillons provenant de différentes sources et des cristaux qui ont été fabriqués en utilisant différentes méthodes de croissance pour nous permettre de mesurer les propriétés optiques intrinsèques de h-BN. Nous rapportons l'impact des symétries des phonons sur la réponse optique du h-BN en effectuant des mesures photoluminescence résolues par polarisation. L’analyse des données en polarisation, nous permet de mesurer la contribution du phonon manquant, celui qui n'a pas été détectée avant cette thèse. En suite, nous démontrons que l'origine de la structure fine du spectre de PL provient pour chaque réplique phonon d’une diffusion complémentaire de type Raman faisant intervenir le mode de phonon E2g à basse énergie (mode de cisaillement inter-feuillets). Les spectroscopies de photoluminescence et de diffusion inélastique Raman ont été combinées pour quantifier l'influence des effets isotopiques sur les propriétés optiques de h-BN ainsi pour révéler que les modifications des interactions de van de Waals liées à l'utilisation de 10B et 11B ou du bore naturel pour la croissance de cristaux h-BN massifs.Enfin, nous étudions des epitaxis de h-BN crues par Épitaxie sous Jets Moléculaires. L'utilisation conjointe de l’imagerie par microscopie à force atomique (AFM) et de la spectroscopie de photoluminescence permet de comprendre la première observation de recombinaison assistée par phonons dans des épitaxies de h-BN sur le saphir et le graphite. Ce résultat indique que la croissance de h-BN à large échelle par méthode épitaxiales est en voie d'acquérir la maturité nécessaire au développement technologique de h-BNHexagonal boron nitride (h-BN) is a wide bandgap (~ 6 eV) semiconductor with a very high thermal and chemical stability often used in devices operating under extreme conditions. The indirect nature of the bandgap in h-BN is investigated by both theoretical calculations and experiments. An indirect excion and phonon-assisted reombinations in h-BN are observed in photoluminescene spectroscopy.This thesis focus on the optical properties of bulk and epilayers of h-BN. We investigated samples from different sources grown different methods in order to confirm the intrinsic optical properties of h-BN. We report the impact of the phonon symmetry on the optical response of h-BN by performing polarization-resolved PL measurements. From them, we will measure the contribution of all the phonon-assisted recombination which was not detected before this thesis. We follow by addressing the origin of the fine structure of the phonon-assisted recombinations in h-BN. It arises from overtones involving up to six low-energy interlayer shear phonon modes, with a characteristic energy of about 6.8 meV.Raman and photoluminescence measurements are recorded to quantify the influence of isotope effects on optical properties of h-BN as well as the modifications of van de Waals interactions linked to utilization of 10B and 11B or natural Boron for the growth of bulk h-BN crystals.Finally, we study h-BN thin epilayers grown by Molecular Beam Epitaxy at Nottingham University, atomic force microscopy (AFM) images and photoluminescence features are combined to confirm the first observation of phonon-assisted recombination in high quality thin h-BN epilayers grown on c-plane sapphire and Highly Ordered Pyrolitic Graphite. This demontrates that large scale growth of h-BN by epitaxy is getting a technologically required maturity
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Roberts, Adam. "Time Domain Spectroscopy of Graphene." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228120.
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This dissertation describes the response of graphene and graphene fragments to ultrafast optical pulses. I will first describe how we created few-cycle optical pulses for interacting with the graphene lattice. These pulses are created through filamentation based pulse compression. I studied how the filamentation process can be optimized through simple means to create the shortest possible pulse. I then examine the extent to which graphene can withstand irradiation from intense ultra-fast pulses. I examine both the high intensity regime at which a single laser pulse will ablate the graphene and a more moderate regime that slowly degrades the graphene from long term exposure to ultrafast pulses. The knowledge lets us both identify a safe working regime for driving the graphene lattice with optical fields as well as use ultrafast lasers to create graphene nano-fragments down to 2nm. Next, I explore the ultrafast dynamics of photo-excited graphene. Graphene undergoes electronic band renormalization after photo exciting carriers. By measuring a differential transmission spectrum, small changes to the band structure can be quantified. I will explain how screened exchange and electron phonon self energies provide corrections to the band structure for different times after carrier excitation. Lastly, I will describe measurements that determine the extent of electron-electron correlations in graphene fragments. By measuring the energy of the two photon state and comparing it the lowest energy one photon state in graphene fragments, we can determine the strength of the correlations in graphene systems.
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Ludlow, Andrew D. "The strontium optical lattice clock: Optical spectroscopy with sub-hertz accuracy." 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:3308676.
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Bru, Jørgen. "Fiber optic probes for biomedical optical spectroscopy." Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9771.
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Optical spectroscopy has been well validated by the physical sciences as a method to characterize chemical compositions in biological material. It has also showed promising to detect atherosclerotic plaques, which can form in the coronary artery walls, and cause heart attacks and strokes. This project seeks to optimize and build fiber optic probes for diffuse reflectance and fluorescence spectroscopy which can assess these plaques. A side-viewing probe is particularly advantageous in the small diameter, confined geometries of arteries. Thus, different techniques are investigated for creating lenses on the tip of optical fibers and design the probes so that they can perform spectroscopic measurements along its circumference. A rigorous testing scheme was developed which included a test matrix and a set of criteria that were used in the optimization process. Two probes for diffuse reflectance and one for fluorescence measurements were built based on the result from the testing scheme. However, a combined probe optimized for both diffuse reflectance and fluorescence measurements could not be created as their respective optimization criteria turned out to be contradictory. The final reflectance probes consisted of two 200 micron fibers separated by 2 mm in the axial direction and the fiber tips were shaped by using a CO2 laser and grinding machine. All the finished probes were tested in a coronary artery of a porcine heart and fat was injected to evaluate their detection of lipid pools. The probes showed good results and were able to detect changes in chromophore content in the tissue and demonstrated the advantages of optimizing a probe for its given application. The fluorescence probe turned out to give good results when used on the arteries from the surface of the heart surface.
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Harley, Eric Chad Toppin McNeil Laurie Elizabeth. "Magneto-optical spectroscopy of dilute magnetic semiconductors." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2006. http://dc.lib.unc.edu/u?/etd,402.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2006.Title from electronic title page (viewed Oct. 10, 2007). " ... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics & Astronomy." Discipline: Physics and Astronomy; Department/School: Physics and Astronomy.
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Reilly, Thomas H. III. "Plasmonic materials for optical sensing and spectroscopy." Diss., Connect to online resource, 2006. 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:3239396.
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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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Harris, Janet Caroline. "Optical spectroscopy of correlated two-dimensional electrons." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390497.
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Robinson, Elizabeth Clare. "Towards broadband optical spectroscopy of single nanostructures." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653073.
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Optical properties of nanostructures strongly depend on their size, shape, material, and local environment. To fully characterise these properties, measurements of the full spectral response are required . The initial challenge is due to the small response of a nanoparticle in an optical field, the extinction. This can be overcome by using interferometry where the field scattered from the nanoparticle is multiplied by a larger reference field. This thesis aims to investigate the use of a broad band supercontinuum source for interferometric detection of single nanostructures.
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Eggleston, James Michael. "Optical spectroscopy of thin film semiconductor structures." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4769/.
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This thesis consists of a study of several thin film semiconductor structures of practical technological use either presently or in the near future. The first system studied is an ultra thin film single crystal gallium arsenide layer. The absorption spectra of these layers are measured and transitions at both the F- point and L-point of the Brillouin Zone are observed, the latter are not normally measurable in thicker layers. The observed shift in the F-point absorption edge is attributed to contributions from the Franz-Keldysh Effect and the Moss-Burstein Effect. The temperature dependence of the L-point energy gap is measured and compared with previous data. The next system investigated is an n-type porous silicon layer coated with p-type polyaniline. Both photoluminescence and electroluminescence spectra and the electrical characteristics have been measured for this system. The interface between the two layers is found to be a rectifying junction consistent with a potential barrier formed at the interface. In forward bias, it is possible to generate electroluminescence in the visible and near infra red regions. The final structure studied is a thin film cadmium sulphide-cadmium telluride solar cell structure. The cells are found to have a low efficiency of around 1% as grown, but a process of treatment with cadmium chloride and annealing in air improves this by a factor of approximately ten. Photoluminescence measurements on the back surface of the cadmium telluride revealed three major emission bands at 1.59 eV, 1.55 eV and 1.45 eV. By varying temperature and incident laser power, attempts at assigning the bands to specific impurity centres in the cadmium telluride is made Using a novel bevelling etch technique to prepare samples, depth dependent measurement of the photoluminescence is possible. This reveals that the major changes associated with the improvement in efficiencies occurs at the interface between the CdS and the CdTe.
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Kirk, James. "Optical transmission spectroscopy of hot Jupiter atmospheres." Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/111014/.
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The field of exoplanet atmospheres has advanced rapidly in the 16 years since the detection of sodium in the atmosphere of HD209458b. Giant planets on short period orbits (`hot Jupiters') have been key to this progression, due to their relatively characterisable atmospheres. Optical transmission spectroscopy revealed the first detection of an exoplanet atmosphere and has continued to play a vital role in atmospheric characterisation. In this thesis I present optical transmission spectroscopy of three hot Jupiters and place these in context within the LRG-BEASTS transmission spectroscopy survey. My ground-based transmission spectrum of WASP-52b revealed the presence of clouds in the planet's atmosphere and evidence for stellar faculae on the host. This study demonstrated that HST precision could be achieved from the ground. I also present ground-based transmission spectroscopy of HAT-P-18b. My precise transmission spectrum was well fitted with a Rayleigh scattering slope at the equilibrium temperature of the planet. The absence of broad sodium and potassium absorption led me to conclude that a high altitude haze was present. Finally I present a transmission spectrum of WASP-80b. I found that a haze was likely present in this planet's atmosphere and my transmission spectrum was inconsistent with a previously claimed detection of pressure-broadened potassium. My results are in agreement with the emerging correlation that cooler planets are less likely to have clear atmospheres. However, this correlation is still tentative. The LRG-BEASTS survey will test this relation and help improve our understanding of the underlying physics driving the formation of clouds and hazes in exoplanet atmospheres.
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Han, Ningren. "Computational and statistical approaches to optical spectroscopy." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120432.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 223-236).
Compact and smart optical sensors have had a major impact on people's lives over the last decade. Although the spatial information provided by optical imaging systems has already had a major impact, there is untapped potential in the spectroscopic domain. By transforming molecular information into wavelength-domain data, optical spectroscopy techniques have become some of the most popular scientific tools for examining the composition and nature of materials and chemicals in a non-destructive and non-intrusive manner. However, unlike imaging, spectroscopic techniques have not achieved the same level of penetration due to multiple challenges. These challenges have ranged from a lack of sensitive, miniaturized, and low-cost systems, to the general reliance on domain-specific expertise for interpreting complex spectral signals. In this thesis, we aim to address some of these challenges by combining modern computational and statistical techniques with physical domain knowledge. In particular, we focus on three aspects where computational or statistical knowledge have either enabled realization of a new instrument-with a compact form factor yet still maintaining a competitive performance-or deepened statistical insights of analyte detection and quantification in highly mixed or heterogeneous environments. In the first part, we utilize the non-paraxial Talbot effect to build compact and high-performance spectrometers and wave meters that use computational processing for spectral information retrieval without the need for a full-spectrum calibration process. In the second part, we develop an analyte quantification algorithm for Raman spectroscopy based on spectral shaping modeling. It uses a hierarchical Bayesian inference model and reversible-jump Markov chain Monte Carlo (RJMCMC) computation with a minimum training sample size requirement. In the last part, we numerically investigate the spectral characteristics and signal requirements for universal and predictive non-invasive glucose estimation with Raman spectroscopy, using an in vivo skin Raman spectroscopy dataset. These results provide valuable advancements and insights in bringing forth smart compact optical spectroscopic solutions to real-world applications.
by Ningren Han.
Ph. D.
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Schmidtke, Johanna Pembrook. "High-pressure optical spectroscopy of conjugated polymers." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612826.
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Chawdhury, Nazia. "Optical and photocurrent spectroscopy of polymeric semiconductors." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624340.
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Nguyen, Hai Truong. "Magneto optical trap recoil ion momentum spectroscopy /." Search for this dissertation online, 2003. http://wwwlib.umi.com/cr/ksu/main.
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Toro, Romain. "Optical spectroscopy of novel quantum dot structures." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5062/.
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This thesis comprises works on novel quantum dot structures. New ways of growing III-V semiconductor quantum dots by integrating a ternary element or by growing on top of a silicon wafer are optically characterized, opening the way to more specific work on those new structures, while furthering our understanding of the epitaxy mechanisms behind them. We study InGaAs/GaAs quantum dot structures monolithically grown on a silicon substrate, without use of germanium virtual substrate nor wafer bonding technique. Optical characterization of the sample with micro photoluminescence is performed and shows very good single quantum dot emission lines. Single photon emission from the InGaAs dots is demonstrated with photon correlation experiment showing clear anti-bunching. Photonic crystal cavities are fabricated for the first time with InGaAs dots monolithically grown on silicon and exhibit very high quality factor up to 13000 with a large percentage of cavities having Q-factors over 9000. This allows observation of Purcell effect for single photon emitting QDs and strong light-matter coupling between InGaAs QDs and cavities. We also investigate unexpected emission lines on the same sample. The lines are identified as interface fluctuations in a GaAs/AlGaAs short period superlattice, making them the first Interface fluctuation quantum dots grown directly on silicon. Further optical characterization confirms the quantum dot nature of the emissions. Polarization measurements allow study of the fine structure splitting of exciton/bi-exciton pairs and the single photon emission of the dots is demonstrated. Finally in a subsequent chapter we investigate InP/GaInP quantum dots with arsenic deposited during the growth process. Magneto-optic PL of samples with different concentrations of As allows to determine how the As changes the characteristics of the dots. Schottky diodes are fabricated and tested to show good characteristics, and electric field experiments demonstrate charge control over this new kind of dots.
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Watson, Frederick Garnett. "Multi-object astronomical spectroscopy with optical fibres." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/27619.
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A full account is given of the relatively new astronomical technique of multi- object spectroscopy with optical fibre lightguides. The thesis begins with a survey of the number densities of a wide range of astronomi- cal object classes, and, after comparing the merits of the various techniques for multi- object spectroscopy, shows (by defining the "effective aperture" of a multiple fibre - coupled telescope) that the multi -fibre tech- nique is very well- suited to the real distribution of celestial objects. A review of the properties of optical fibres is given, together with an exposition of the important considerations in the design of fibre feeds for astronomy. This is followed by a description of the requirements in the design of telescopes, spectrographs and detectors to render them suitable for the multi -fibre technique. Equations are derived for the performance of these systems in terms of signal -to -noise ratio, and an example is given. A survey of the equipment that has been built for multi -fibre spectroscopy at observatories throughout the world is presented, and special attention is paid to the FOCAP fibre system at the 3.9 -metre Anglo- Australian tele- scope. The thesis gives an example of the use of FOCAP in work carried out by the writer to investigate the kinematics of RR Lyrae variables in the nuclear bulge of the Galaxy. Evidence is found in the preliminary results for the existence of non -circular motions along the galactic centre line -of- sight. A description is then given of the FLAIR wide -field fibre -coupled multi- object spectroscopy system built by the writer for the 1.2 -metre UK Schmidt Telescope. Reports are presented on a series of observational pro- grammes designed to test the system, including the classification of stars in the Chamaeleon dark cloud, spectroscopy of Orion cluster flare stars, spectroscopy of objects in the Large Magellanic Cloud, the measurement of galaxy redshifts, and the observation of quasar candidates. An experiment in time -resolved multi- object photometry is also described. It is shown that for spectroscopy, the prototype system will perform well on stellar targets to V "16 -17, but, although galaxy redshifts have been obtained, its usefulness for the systematic measurement of redshifts is hampered by its low sensitivity in the blue region of the spectrum. An account is then given of the relatively simple steps needed to rectify this, together with a brief description of a proposed, fully- optimised FLAIR system. Finally, the future prospects for multi -fibre astronomical spectroscopy are briefly reviewed, from the point of view of the new instrumentation becoming available, and the astronomical results that will be produced.
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Zeng, Hualing. "Optical properties of single walled carbon nanotubes." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/b40203979.
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Zeng, Hualing, and 曾華凌. "Optical properties of single walled carbon nanotubes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40203979.
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Carlson, David R. "Frequency Combs for Spectroscopy in the Vacuum Ultraviolet." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/612874.
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This dissertation explores frequency comb spectroscopy and, in particular, its extension to the vacuum-ultraviolet (VUV) and extreme-ultraviolet (XUV) wavelength regimes through a technique called intracavity high harmonic generation (IHHG). By combining the techniques of passive pulse amplification in an enhancement cavity with high harmonic generation, IHHG enables the direct conversion of near-infrared radiation to the VUV/XUV while still maintaining the underlying comb structure .As part of this work, a series of numerical simulations was performed to investigate the plasma that is formed in the IHHG process and its implications for the resulting VUV comb. It was demonstrated that a fundamental limitation to the performance of IHHG experiments is due to the single-pass ionization phase shift acquired by the pulse circulating in the enhancement cavity. Furthermore, we showed that a static background plasma accumulates between pulses and complicates cavity stabilization. Insights gained from the simulations led to the development of a novel pump-probe technique using the enhancement cavity that allowed a direct measurement of the intracavity plasma and its decay dynamics in real-time. Because the plasma lifetime plays such a crucial role in the operation of these cavities, it was important to have a method to test ways of reducing it. To build on our initial IHHG results showing record-level powers in the XUV, we implemented a fully phase-coherent dual comb spectrometer consisting of two identical IHHG systems operating in parallel. The system is designed for precision spectroscopy in the VUV and is based on a pair of homemade ytterbium fiber lasers that use a parabolic amplification scheme to achieve 80 fs pulses after amplification to 50 W of average power. Initial dual comb data showing system performance at the fundamental frequency and third harmonic are presented.
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HOLM, DAVID ALLEN. "QUANTUM THEORY OF MULTIWAVE MIXING (RESONANCE FLUORESCENCE, SATURATION SPECTROSCOPY, MODULATION, PHASE CONJUGATION, QUANTUM NOISE)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187980.
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This dissertation formulates and applies a theory describing how one or two strong classical waves and one or two weak quantum mechanical waves interact in a two-level medium. The theory unifies many topics in quantum optics, such as resonance fluorescence, saturation spectroscopy, modulation spectroscopy, the build up of laser and optical bistability instabilities, and phase conjugation. The theory is based on a quantum population pulsation approach that resembles the semiclassical theories, but is substantially more detailed. Calculations are performed to include the effects of inhomogeneous broadening, spatial hole burning, and Gaussian transverse variations. The resonance fluorescence spectrum in a high finesse optical cavity is analyzed in detail, demonstrating how stimulated emission and multiwave processes alter the spectrum from the usual three peaks. The effects of quantum noise during the propagation of weak signal and conjugate fields in phase conjugation and modulation spectroscopy are studied. Our analysis demonstrates that quantum noise affects not only the intensities of the signal and conjugate, but also their relative phase, and in particular we determine a quantum limit to the semiclassical theory of FM modulation spectroscopy. Finally, we derive the corresponding theory for the two-photon, two-level medium. This yields the first calculation of the two-photon resonance fluorescence spectrum. Because of the greater number of possible interactions in the two-photon two-level model, the theoretical formalism is considerably more complex, and many effects arise that are absent in the one-photon problem. We discuss the role of the Stark shifts on the emission spectrum and show how the Rayleigh scattering is markedly different.
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Schmidt, Michael [Verfasser]. "Optical Spectroscopy on Triangular Lattice Antiferromagnets / Michael Schmidt." München : Verlag Dr. Hut, 2015. http://d-nb.info/1067708952/34.
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Qasim, Hasan, and hasanqasim05@gmail com. "Optical spectroscopy characterization of nano-scale photonic structures." RMIT University. Science Engineering and Technology, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080829.162734.
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Current micro-scale electronics technology has been approaching rapidly towards its technological limit. This has shifted the focus towards nano-scale technology in recent years. More and more researchers around the globe are working in pursuit of bringing nano-scale technology into mainstream. The research carried out here is a small step towards a similar goal. The remarkable optical properties exhibited by certain nano-scale structures are in stark contrast to their bulk form and this provides the basis for this research. Two kinds of nanostructures are developed and investigated for their optical properties. One of these is nanofibers processed from a polymer known as polyaniline (PANI). The focus of this study is to investigate its optical and conductive properties under different conditions of doping environments, temperature and polymerization conditions. Optical characterization technique such as UV-Visible spectroscopy is developed to carry out the investigation. The developed nanofibers have been demonstrated to possess optical and conductive properties to be dependent on doping variables. Study of these optical properties could prove very useful in the development of electrochromic devices and gas sensors. Later in the research, UV-Visible spectroscopy has been improved into a low cost Raman spectroscopy setup which is validated by experimentation carried out on some samples. The second type of nano-structure developed and investigated, is an array of nanoparticles of noble metals such as gold and silver. Such an array is shown to exhibit a phenomenon called plasmon resonance effect when excited by light. UV-Visible spectroscopy technique is utilized to investigate this effect for metal nano-arrays. A biologically nano-structured surface (wing of an insect called cicada) is used as the substrate for the fabrication of metal array. A serious attempt has also been made to do 'Surface Enhanced Raman Spectroscopy (SERS)', making use of the metal nano-array developed. This technique improves the raman lines intensities of certain less sensitive samples such as thiophenol, which are known to give weak raman lines. This is carried out by adsorbing the sample on the metal nano-array.
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Day, S. "Neutron and optical spectroscopy of alkaline earth metals." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234944.
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Holmes, Mark J. "Optical spectroscopy of wide bandgap semiconductor nanoscale structures." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:b8318654-dd3a-4875-8a8e-1e57d877b0f2.
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The optical properties of GaN nanocolumn structures containing InGaN quantum disks are investigated by optical microphotoluminescence spectroscopy using pulsed lasers, and cathodo- luminescence. The results are analyzed in the context of current theories regarding an inho- mogeneous strain distribution in the disk which has been theorized to generate lateral charge separation in the disks by strain induced band bending, an inhomogeneous polarization field distribution, and Fermi surface pinning. Simulations of the strain distribution for the relevant materials and structures are also performed, and the results analysed. It is concluded from ex- perimental measurements that no extreme lateral separation of carriers occurs in the quantum disks under investigation. Internal field screening by an increased carrier density in the QDisks at higher excitation densities is observed via a blue-shift of the emission and a dynamically changing decay time. Other possible explanations for these effects are discussed and discounted. Microphotoluminescence studies are also carried out on a single GaN nanocolumn struc- ture that has been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in the vicinity of the InGaN QDisk in addition to a delayed emission from the QDisk relative to the GaN is observed. Time resolved spatial maps of the luminescence intensity from the column are also presented, illustrating the evolution of the carrier density in the system. Additional, albeit early-stage, work on novel structures based on the production of GaN nanocolumns, namely nanotubes and nanopyramids, is also presented.
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Adams, Stephen J. A. "Optical spectroscopy of InxGa1-xAs/GaAs quantum wells." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/816.
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Prior, Louise Ann. "Magneto-optical spectroscopy of bacterial nitric oxide reductase." Thesis, University of East Anglia, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398797.
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Kazmi, Syed Sibghat Ullah. "Optical spectroscopy and susceptibility studies of magnetic dimers." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252735.
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Mignuzzi, Sandro. "Near-field optical spectroscopy of two-dimensional materials." Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/nearfield-optical-spectroscopy-of-twodimensional-materials(2e5e7a6b-d2b5-4242-bab7-3a66bd6c8c25).html.
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Real materials contain structural defects which significantly affect their properties. Defects, in a general sense, are ubiquitous and encompass the diverse variety of elements capable of disrupting the continuity and translational symmetry of a crystalline lattice, both in terms of its structural morphology, and in terms of local modulation of its electrical and optical properties. In this perspective, atomic vacancies, line vacancies, atomic rearrangements, local doping inhomogeneity, chemically adsorbed adatoms, all fall within the broad category of defects. Thus, the nanoscale details of surface structure plays a pivotal role in understanding the impact defects may have on the overall properties of the material, and this is particularly true for "all-surface" materials such as two-dimensional (2-D) crystals. Even the interface between two atomically thin layers has a strong impact on the electronic and optical properties of few-layered stacks; therefore, also the interface associated with stacking and layer orientation can be viewed as an extend defect in two dimensions. While macroscopic morphological characterization methods can provide averaged information over a lateral extent defined by their spatial resolution, high resolution (i.e. nanoscale) imaging has the potential to unveil important insights into the role of defects that dominate several aspects of surface chemistry and physics. On the one hand, defects in 2-D materials can be seen as deleterious as they may alter their electrical, chemical, magnetic and mechanical properties. On the other hand, the intentional creation of nanoscale defects may offer an additional degree of freedom for engineering their properties. In this perspective, having structural defects can be either detrimental or beneficial, depending on the targeted application. Despite the ever expanding literature on the study of the interplay between defects and the optical, electrical and mechanical properties of two dimensional materials, direct and non-destructive imaging of defect formation at the nanoscale remains a significant challenge. Although techniques such as electron microscopies or scanning tunnelling microscopy can be used to resolve individual lattice defects, they may be destructive or restricted to specific (e.g. conductive) substrates. This thesis presents a nanoscale optical investigation of 2-D materials, such as graphene and single-layer MoS2, with a particular focus on the characterisation of defects. The field enhancement at the tip-apex of a metal-coated atomic force microscopy (AFM) tip is used to decrease the spatial resolution beyond the diffraction limit. In the case of the investigation of Raman scattering, this near-field optical technique is known as tip-enhanced Raman spectroscopy (TERS). TERS is here demonstrated to be a valid technique to probe the distribution of point-like defects at the nanoscale, especially in the case of barely defective graphene. An analytical model to describe near-field imaging of pointlike Raman scatterers, which is of general applicability to zero-dimensional scatterers such as molecules, is presented. The near-field image, constructed from the Raman intensity, is found to depend on the Raman tensor and the orientation of the scatterer. The model can be also used to explain the different values of near-field Raman enhancement observed for different Raman bands. Motivated by the successful optical characterization of defects in graphene by means of Raman spectroscopy, it is now timely to expand the study of structural defects to other 2-D materials, such as semiconducting transition metal dichalcogenides. MoS2 is one of the most prominent members of this newly discovered category of chalcogenide monolayers. Defect-induced Raman scattering of single-layer MoS2 is studied by means of a controlled introduction of defects using ion-bombardment. Phonon confinement is used to explain the evolution of peak widths and shifts, and a metric based on Raman intensities is proposed to quantify defects. To gain insight into the defect-induced Raman processes, polarised and resonance Raman spectroscopy are employed.
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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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Becker, Klaus-Dieter. "Optical spectroscopy for studying dynamic and kinetic processes." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186691.
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Bergin, Ann G. V. "Applications of optical-feedback cavity-enhanced absorption spectroscopy." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:26ecc3d0-2aa1-4d21-a698-dc362956280b.
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This thesis presents two contrasting implementations of the optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) technique. OF-CEAS com- bines passive optical-feedback locking of semiconductor lasers with cavity-enhanced absorption spectroscopy, and is well suited to sensitive detection of pressure- broadened trace gases. Chapters 1 and 2 set the work in this thesis in context, by describing the theory and discussing the motivations behind trace gas sensing by tuneable laser spectroscopy in the near- and mid-IR. Chapter 3 reviews the theory of OF-CEAS, prior to presenting the results of an experimental implementation based on a near-IR DFB diode laser setup following the traditional V-cavity methodology to spatially decouple the optical- feedback beam from the direct back reflection. The capabilities of the system are demonstrated by accurate determination of a self-broadened half-width at half- maximum of a CO 2 transition, and by detection of acetylene in a car exhaust sample. Chapter 4 describes the design and implementation of the linear cavity method- ology for QCL OF-CEAS, which is the significant contribution of this work. Successful OF-CEAS locking with the linear cavity is shown for two different DFB-QCLs, with close operating wavelengths (5.5 and 5.2 µm) but quite different operating powers and facet size. Chapter 5 presents quantitative spectroscopic results from the linear cavity OF-CEAS instrument, using both lasers. Spec- troscopy on mixes of N 2 O and NO returned sensitivities, quantified by the α min , of 2.7 × 10 −8 cm −1 in 1 s at 0.28 atm and 2.4 × 10 −8 cm −1 in 1 s at 0.19 atm respectively. Limited by etalon fringing on the baseline, the α min compared well with those obtained with V-cavity QCL OF-CEAS instruments. The temporal stability was investigated by Allan variance calculations and the best minimum detectable concentrations for the linear QCL OF-CEAS instrument were 32 ppm for N 2 O (35 s) and 5 ppb for NO (2 s). For NO, this detection limit compares favourably with other mid-IR QCL-based NO sensors, and is sufficient for mon- itoring NO in polluted urban environments. With the Maxion DFB-QCL, mon- itoring of NO in air outside the laboratory was attempted, and an air sample drying system benchmarked. Although this experiment proved unsuccessful, it was possible detect trace amounts of NO desorbing from the walls of the gas cell. Over the course of one hour the concentration rose from 3.8 ± 0.7 ppb to 28.4 ± 0.2 ppb, leading to a rate of desorption of 6.76 ± 0.01 × 10 −3 ppb s −1 . The sensitivity (α min ) of these spectra was 7.0 × 10 −9 cm −1 in 1 s, improved due to the higher mirror reflectivity at the lasing wavelength of the Maxion DFB-QCL, although still limited by etalon fringing.
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Kim, Hee Dae. "Optical spectroscopy of a single GaAs quantum ring." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:dba56f5f-06eb-434f-a41d-524f63e59399.
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Given their unique structural properties, quantum rings (QRs) structures have recently been of particular interest for investigating quantum interference which is called the neutral charged exciton optical Aharonov-Bohm (AB) effect. A delocalized wavefunction around the rim is a prerequisite for the AB effect, but asymmetry and anisotropy seem to have been overlooked in the spectroscopy of QRs. In this thesis, the presence of a localized state in a single GaAs QR is presented.