Dissertations / Theses on the topic 'Optical pumping'
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1
Favorskiy, Igor. "Optical pumping in Silicon thin films." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00950979.
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Grâce à un long temps de vie de spin, le silicium est un matériau prometteur pour l'électronique de spin. Mais les approches classiques d'étude de la dynamique de spin basées sur la luminescence polarisée ne peuvent pas être utilisées dans ce matériau à cause du faible couplage spin-orbite et du gap indirect. Dans ce travail, nous avons étudié la polarisation de spin des électrons de conduction créée en condition de pompage optique par spectroscopie de photoémission. La surface du silicium est activée en affinité négative par dépôt de césium et d'oxygène de sorte que les électrons photoexcités avec une énergie proche du gap peuvent émis dans le vide. Nous utilisons un laser accordable qui permet de mesurer systématiquement le spectre de polarisation pour des énergies d'excitation allant du seuil d'absorption jusqu'à la bande Gamma2- au-dessus du gap direct. Nous avons obtenus les spectres de polarisation à partir de couches minces SOI d'épaisseurs différentes. A partir de ces résultats, nous déterminons la valeur de paramètres importants de la structure de bande comme le gap direct ou l'énergie du couplage spin-orbite. Cependant, contrairement aux prédictions, lorsque l'épaisseur de la couche de silicium diminue jusqu'à des valeurs inférieures à la longueur de diffusion de spin, la polarisation en spin des électrons émis reste proche de zéro (-0.4%), remettant en cause l'interprétation directe des valeurs théoriques de la polarisation initiale égale à -20%. Une approche théorique a donc été développée sur la base d'un modèle ab initio de structure de bande pour déterminer les spectres de polarisation en spin. Ces calculs sont encore en cours, mais les résultats déjà obtenus sur la structure électronique du silicium sous contrainte indiquent une piste intéressante pour les études futures.
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Taylor, Jason Matthew 1977. "Shaped ultrafast optical pumping for NMR applications." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/88353.
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Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2002.Includes bibliographical references (leaves 104-108).
by Jason Matthew Taylor.
S.M.
3
Johnston, Colin I. "Optical and electrical pumping of colour-centre media." Thesis, University of St Andrews, 1991. http://hdl.handle.net/10023/13756.
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Within this thesis the exploitation of the large homogeneously broadened bandwidth of the LiF:F+2 colour-centre laser by production of frequency tunable ultrashort optical pulses over the 0.8-1.0mum spectral region has been presented. A synchronously pumped LiF:F+2 colour-centre laser produced pulses of 700fs duration with average powers of 30mW when a colliding-pulse-modelocked travelling-wave cavity was implemented. Passive modelocking of the LiF:F+2 colour-centre laser was achieved over two spectral operating regions centred around 860nm and 930nm when the saturable absorber dyes IR140 and DaQTeC were employed. Pulse durations as short as 180fs and 130fs were obtained at 860nm and 930nm respectively using colliding-pulse-modelocked group-velocity-dispersion compensated resonators. The laser was pumped at a 10% duty cycle throughout. The use of coupled-cavity- modelocking techniques combined with passive modelocking was found to extend both the tuning range of the laser and useful operating lifetime of the saturable dye. A home built NaCl:OH- colour-centre laser which encorporates the stabilised F+2 colour- centre is presented. Output powers of up to 450mW were obtained for input pump powers of 4W and the laser tuned from 1.4-1.8?m. Electroluminescence studies of NaCl, CsI, CsI:Na, CsI:Tl, and KI crystals are also presented in a study to assess the feasibility of obtaining laser action from such materials by electrical excitation. KI is shown to be the favoured laser candidate by this excitation method and evidence of temporal narrowing and signal enhancement of the electroluminescence output is presented.
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Kumar, Yogesh. "Studies on optical pumping of semiconductor optical amplifier for fast gain recovery." Thesis, IIT Delhi, 2016. http://localhost:8080/iit/handle/2074/7067.
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Swoger, James Harvey. "On non-uniform pumping effects in semiconductor lasers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ30171.pdf.
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Tabor, David. "Toward Rotational Cooling of Trapped SiO+ by Optical Pumping." Thesis, Northwestern University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3627205.
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This thesis presents a scheme for preparation of trapped molecular ions with a high degree of internal state purity by optical pumping with a broadband pulse-shaped femtosecond laser; the internal structure of SiO+ permits fast stepwise pumping through the tens of rotational levels populated in a room-temperature distribution. Two analyses, which guided the experimental implementation, are presented: (1) a novel method of quantifying anharmonicity in the trapping potentials, which limits the number of ions that can be trapped, and (2) a rate-equation simulation of the quantum state evolution during pumping. Experimental implementation of pulse shaping and its characterization are discussed, as is the molecular spectroscopy used to reference this light to the rotational cooling transitions. Internal state analysis can be performed using resonance enhanced multiphoton dissociation.
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Ferguson, A. H. "Far infrared optical pumping and laser magnetic resonance spectroscopy." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382213.
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Norquay, Graham. "Spin-exchange optical pumping and nuclear magnetic resonance of 129Xe." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/12940/.
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The nuclear spin polarisation of 129Xe can be increased by four to five orders of magnitude using the technique spin-exchange optical pumping. The resulting enhancement in polarisation can be utilised to dramatically enhance the sensitivity of 129Xe in nuclear magnetic resonance (NMR) applications. This thesis is concerned with the physics of spin-exchange optical pumping and NMR spectroscopy of hyperpolarised 129Xe. Its general aims are to optimise the production of hyperpolarised 129Xe and to evaluate the underlying NMR mechanisms of 129Xe in blood (in vitro and in vivo). Chapters 3 and 4 detail experiments and modelling on a spin-exchange optical pumping polariser with the aim to optimise the production of hyperpolarised 129Xe for nuclear magnetic resonance NMR spectroscopy. This optimisation has enabled high-quality imaging of the airspaces of the human lungs as well as spectroscopy of 129Xe dissolved in blood and lung tissue. In addition to 129Xe polarisation optimisation, in Chapter 5, NMR experiments on 129Xe in human blood were performed to determine constants underpinning 129Xe NMR relaxation and exchange dynamics in whole blood samples. These constants should enable accurate modelling of 129Xe signal dynamics during in vivo experiments involving xenon transport from the lungs to distal tissues. Lastly, in Chapter 6, hyperpolarised 129Xe NMR was used to probe pulmonary blood oxygenation in vivo. A non-linear relationship between the 129Xe chemical shift in red blood cells was determined in vitro on human blood samples at 1.5 T and 3 T. This relationship was used for dynamic measurements of pulmonary blood oxygenation in a healthy volunteer during breath-hold apnoea on a 3 T scanner.
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Flinn, Gregory Patrick. "Laser spectroscopy of semiconductor quantum wells : optical pumping and optically detected nuclear magnetic resonance." Thesis, University of Southampton, 1991. https://eprints.soton.ac.uk/399448/.
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This thesis describes the experimental results of optical pumping studies made in some Type 1 GaAs/Al0.3Ga0.7As single quantum wells (QWs), ranging in widths from 50 to 200A. Optical pumping uses circularly polarised light to photocreate spin orientated carriers in the QWs. The polarised carriers, principally the electrons, transfer angular momentum to the nuclear spins of the lattice through the Fermi contact hyperfine interaction. The orientated nuclei act back on the electrons through the same interaction. Studies of the nuclear and carrier spin systems may be effected by monitoring the circular polarisation of the recombination luminescence. The Hanle Effect of the electron orientation within the QWs is measured as a function of well width, and of the non-photoexcited hole concentration. Correlation of this data with carrier recombination time measurements produces the magnitude of the carrier Landé factor. Allowing the nuclear field to influence the Hanle curves determines the sign of these g - factors, whence the free conduction electron value is observed to change sign at 55A and become positive for thinner wells. This result is compared to the bulk g -values of GaAs (-0.44) and Al0.3Ga0.7As (+0.40), and modelled using k . p theory to estimate the contributions to g* from the well and barrier materials. Nuclear orientation within the wells is observed by the optical detection of nuclear magnetic resonance (ODNMR), via the application of a radio frequency field (RF) to the orientated nuclear spins. ODNMR of ~ 1011 nuclear spins is measured in almost all the single QWs. The signals are studied as a function of various experimental influences, such as well width, p-type carrier concentration, RF magnitude, optical pumping time, and RF sweep rate. Observation is made of extrinsic lattice strain and spin diffusion of the nuclear magnetization, and results suggest increased nuclear relaxation rates within the barrier. n-type wells show no ODNMR, indicating that incomplete hole relaxation is present within the wells. The very wide and undisplaced Hanle curves observed in this type of well support this view. Nuclear orientation is not observed in some GaAs/InxGa1-xAs QW systems. This null result is discussed in terms of the experimental factors important for its successful observation in the GaAs/Al0.3Ga0.7As systems.
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Heitmann, Filip August. "Zinc Oxide Nanolaser : Photoluminescence spectroscopy and optical pumping of zinc oxide nanowires." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16785.
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This Master's thesis is a continuation of the specialization project I did during the spring of 2011. The goal of said project was to set up a system for UV-photoluminescence experiments in the Nanophotonics laboratory at the Department of Electronics and Telecommunications at NTNU, and conduct photoluminescence spectroscopy measurements on different zinc oxide nanostructures, including GaAs/AlGaAs/ZnO core/multishell nanowires. This thesis involves studying zinc oxide nanowires using both a continuous wave and pulsed ultraviolet laser light, and the final goal is to optically excite these nanowires so they achieve lasing. Using a Tsunami Ti:sapph mode-locked tunable laser and a flexible harmonic generator, laser pulses with a pulse duration of 2 ps could be generated at wavelengths around 300 nm, at a power of around 5 mW. At this power, some of the wires showed possible signs of optical gain, but since it was not possible to apply more power to the wires, this could not be confirmed. If there had be enough time, both low temperature measurements and time-resolved spectroscopy, using a streak camera, would have been performed.
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Matsuda, Fuyuki. "TOPOLOGICAL PHASES OF COLD ATOMS IN OPTICAL SUPERLATTICE." Kyoto University, 2020. http://hdl.handle.net/2433/259720.
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Wu, Jingwei, Xiushan Zhu, Valery Temyanko, LaComb L. Valery, R. A. Norwood, and N. Peyghambarian. "Power scaling of single-frequency fiber amplifiers at 976 nm." IEEE, 2016. http://hdl.handle.net/10150/622788.
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Cladding pumped single-frequency Yb3+-doped fiber amplifiers at 976 nm were investigated. Over 4 W output power was obtained and further power scaling can be achieved by reducing the cladding diameter of the Yb3+-doped fiber.
13
Yip, Ka Wa. "Optical pumping of multiple atoms in the single photon subspace of two-mode cavity QED." Miami University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=miami1438288697.
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Newton, Hayley Louise. "Hyperpolarised xenon production via Rb and Cs optical pumping applied to functional lung MRI." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14339/.
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Hyperpolarisation encompasses a multitude of methods to increase the species' spin polarisation for nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications. Hyperpolarised 129Xe is produced via spin-exchange optical-pumping (SEOP). Firstly, electronic spins of alkali metal vapour are polarised via absorption of circularly polarised light. Alkali metal polarisation is subsequently transferred to noble gas nuclei via collisions. Within this thesis, the SEOP process is examined by probing the kinetics of the 129Xe polarisation build up. A combination of diagnostic techniques are used including low field NMR to measure 129Xe polarisation (PXe) at different spatial positions, near-IR optical absorption to give a global estimate of the alkali metal polarisation, and in situ Raman spectroscopy to spatially monitor the energy transport processes by detecting the internal gas temperatures (TN2). TN2 values were found to be dramatically elevated above oven thermocouple readings, with observations of up to 1000 K for an oven heated to only 400 K. Internal gas temperatures are presented for the first time along the length of the optical cell, showing spatial temperature and PXe variations during steady state and rubidium runaway conditions. Two contrasting methods of Raman spectroscopy are examined: a conventional orthogonal arrangement of detection and excitation optics, where intrinsic spatial filtering of the probe laser is utilised; and a newly designed inline module with all components in the same optical plane. Optical filtering is used to reduce the Rayleigh scattering and the probe laser line. This new inline device is presented herein and has a 23 fold improvement in signal to noise enabling increased accuracy and precision of `real-time' temperature monitoring. Rubidium, caesium and a rubidium/caesium hybrid are compared as the alkali metal of choice in the SEOP process. Caesium has a higher spin-exchange cross-section with 129Xe, thus a system is envisaged where current Rb D1 lasers in many polarisers can be utilised with a Rb/Cs hybrid to gain improvements in polarisation rates or levels. Xenon polarisations are shown up to 50% for a hybrid cell. Finally, preparatory experiments crucial to the imminent lung imaging study are presented, including measurements of PXe at low and high magnetic fields. In addition, polariser technology is examined including the current Nottingham device and an open-source consortium polariser.
15
Skinner, J. G. "Optimisation of xenon-rich stopped-flow spin-exchange optical pumping for functional lung imaging." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/41416/.
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Spin-exchange optical pumping (SEOP) is a hyperpolarisation method used in the hyperpolarisation of noble gases and can enhance nuclear spin polarisation by five orders of magnitude. Hyperpolarised (HP) 129-Xe has many properties that make it ideally suited to clinical lung imaging, but since its first demonstration in animals in 1994 and humans in 1996, translation to the clinic has been hampered by challenges associated with scaling up production. Within this thesis, construction and demonstration of a clinical-scale stopped-flow hyperpolariser is described, the design of which is based on the record holding XeUS and XeNA polarisers developed previously by our consortium, which had aimed to address the issue of production scale-up. Modifications enhancing the ease of operation and utility in-clinic are presented, as are modifications that reduce the capital cost of such a system. These include a re-design of the gas manifold and the development of a low-cost low-field NMR spectrometer which achieved an SNR of 125 at a cost of ~$300, a 13-fold improvement in cost/SNR compared with the existing spectrometer at a saving of ~$19,000. In continuous-flow 129-Xe polarisers there has long been a discrepancy in the polarisation achieved and that predicted by the standard model of SEOP which was shown recently to be due to the presence of rubidium clusters. Here, the standard model is applied to- and validated for the first time against the stopped-flow regime. The validated model is used to explore parameter space to identify the most effective ways to increase production yield in future stopped-flow polarisers. Stopped-flow SEOP in the xenon-rich regime presents unique thermal management problems due to the absence of gas flow and abundance of poorly thermally conductive, Rb spin destroying Xe. Raman spectroscopy is used to spatially examine in-cell thermal behaviour under steady-state and turbulent 'rubidium runaway' conditions as a function of temperature and Xe density and the beneficial impact of adding thermally conductive helium to the standard N2-Xe gas mix is demonstrated. Hybrid Rb-Cs-Xe SEOP is demonstrated for the first time and examined using in-situ NMR and Raman spectroscopies. High polarisations of ~50% were obtained. Finally, progress on the HP-Xe clinical trial is presented to illustrate the impact of the 4-fold increase in SNR that will come with the installation of the new N-XeUS stopped-flow polariser.
16
Ranta, Kaili. "Clinical-Scale Hyperpolarization of 129Xe and 131Xe via Stopped-Flow Spin Exchange Optical Pumping." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/dissertations/1282.
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The fundamental physics of spin-exchange optical pumping (SEOP) has been explained in detail by many brilliant scientists since its discovery in the 50’s and 60’s. Although some interactions remain only tenuously understood, mathematical relationships have been mapped across many trajectories with meticulous care. Despite these foundational descriptions, many of the larger scale dynamics remain capricious in practice, especially as SEOP strives to take advantage of rapidly developing laser technologies. This presents a difficulty for implementing the large-scale production of hyperpolarized gases that is required for clinical and some specific experimental applications. This research, performed over the past four years, was designed to shed light on some of the practical effects that become critical for scaling up production while keeping polarizations high, particularly in a “stopped-flow” polarizer environment. This dissertation is divided into eight main chapters. The first chapter is written to provide a historical context for the SEOP field and summarize the evolutionary stages that have led to current methodologies. The second chapter provides a brief summary of SEOP theory and mathematically outlines the transfer of quantum order from photon polarization, to electron polarization via optical pumping, and finally to long-lived nuclear polarizations via spin-exchange. Chapter 3 discusses the practical implementation of SEOP, and the specific designs and techniques used throughout this project to create and monitor polarization. Chapter 4 presents data with some unexpected trends collected by Dr. Nicholas Whiting and Dr. Peter Nikolaou using high densities of xenon and high resonant laser powers. This data inspired a set of simulations designed to locate the cause of these trends, and map the expected trajectory for further studies. Chapter 5 features a clinical-scale polarizer with 170 W of highly resonant cw laser power, capable of producing >0.8 L of hyperpolarized gas per SEOP cycle with 129Xe polarization values of ~30-90% (depending on the xenon density). Multidimensional data maps were created over various temperatures, gas mixes, and laser powers; the results are used to guide optimal performance and describe the conditions that cause SEOP to fail. Chapter 6 reintroduces helium into stopped-flow gas mixes to help mitigate the central difficulties found in Chapter 5 with thermal regulation, and discusses the improvements and difficulties observed as a result. Chapter 7 contrasts the tactics for high 129Xe polarization with the strategies that lead to high 131Xe polarization. Specifically this study is designed to assess whether 131Xe is capable of becoming polarized via SEOP to sufficient levels—and in sufficient amounts—to be used for some specific fundamental physics studies and other biomedical applications. Finally Chapter 8 presents a short proof of concept for the use of an aluminum optical pumping cell instead of the glass optical pumping cells predominantly used for SEOP.
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Lohse, Michael [Verfasser], and Immanuel [Akademischer Betreuer] Bloch. "Topological charge pumping with ultracold bosonic atoms in optical superlattices / Michael Lohse ; Betreuer: Immanuel Bloch." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/115509767X/34.
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Adamovich, Igor V. "Studies of nonequilibrium vibrational kinetics of carbon monoxide and nitric oxide in optical pumping experiments /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu148784730905197.
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Sun, Xuan. "A study of ion acceleration, asymmetric optical pumping and low frequency waves in two expanding helicon plasmas." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4319.
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Thesis (Ph. D.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains v, 152 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.
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Haine, Simon A. "The stability of a continuously pumped atom laser." View electronic text, 2002. http://eprints.anu.edu.au/documents/disk0/00/00/06/62/index.html.
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Thesis (BSc. (Hons))--Australian National University, 2002.Available via the Australian National University Library Electronic Pre and Post Print Repository. Title from title screen (viewed Feb. 18, 2003). "A thesis submitted as partial fulfillment of the requirements for the degree of Bachelor of Science with Honours in theoretical physics at the Australian National University" Includes bibliographical references.
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Al-Jourani, Mohanned M. A. W. "Applications of COâ†2 lasers to optoacoustic vapour detection and optical pumping of far-infrared lasers." Thesis, Keele University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358721.
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CORREA, VALDER O. "Laser de Nd:YLF bombeado lateralmente." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9296.
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Made available in DSpace on 2014-10-09T12:25:50Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:03:32Z (GMT). No. of bitstreams: 1 11317.pdf: 3423206 bytes, checksum: bf89075f85fedad2515b1bf4995078c2 (MD5)
Dissertacao (Mestrado)
IPEN/D
Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP
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Akin, Ryan E. "Minimally invasive assessment of lymphatic pumping pressure using near infrared imaging." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47536.
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Although the major functions of the lymphatic system are fairly well defined, its vasculature has yet to be well characterized in comparison to its blood vasculature counterpart. Recent advances in optical imaging techniques have allowed for more detailed and quantitative evaluations of lymph flow dynamics and mechanism. A rat tail is often used for investigations of lymph flow because of the simple geometry, superficial nature, and disease progression models of its collecting lymphatic vessels. In this study, a pressure cuff system was fabricated and coupled with an existing functional near infrared (NIR) imaging system to measure the overall pumping pressure of the lymphatic vessels of a rat tail. In addition to adapting the system for use on rodents, previous systems used for measuring lymphatic pumping pressure in humans were improved upon in several ways. The system defined here utilizes closed-loop feedback control of pressure application at smaller, more precise intervals. Using this device, a significant difference in lymphatic vessel pumping pressure was detected between a control case and a treatment case in which a vasoactive substance with a nitric oxide donor (GTNO ointment) was applied to the tail. Although it is known that nitric oxide plays a crucial physiologic role in propagation of flow through lymphatic vessels, this study has quantified its significant pharmacological reduction of pumping pressure for the first time.
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Sezgin, Kubilay. "Pumping Chamber Design In Diode-pumped Solid-state Lasers For Maximum System Efficiency And Minimum Optical Distortion." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615397/index.pdf.
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The beam quality and the system efficiency of a diode-pumped solid-state laser source are directly
related to the thermal profile inside the laser crystal. The thermal profile in a laser crystal should be
made uniform in order to reduce the negative effects of the thermal lens. However, the absorbed pump
profile that forms a uniform thermal profile inside the gain medium may adversely affect the system
efficiency. In this thesis, a computational and empirical method was developed for designing pumping
chambers that results in a suitable thermal profile inside the gain medium, and thus desired laser beam
quality was achieved while keeping the system efficiency at an acceptable level. Accomplishment of
this thesis work will lead to the design of pumping chambers and resonators in high power laser
systems operating at even higher thermal loads.
25
Birchall, Jonathan R. "Characterisation of Rb and Cs spin-exchange optical pumping for application to hyperpolarised 129Xe functional lung MRI." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/46779/.
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When performing nuclear magnetic resonance (NMR) it is desirable to maximise the available polarisation of the spin system in order to achieve optimal signal-to-noise ratios. One method of achieving this is via the process of spin-exchange optical pumping (SEOP). SEOP can be used to produce hyperpolarised (HP) noble gases, which possess numerous applications in the fields of science and medicine, ranging from spectroscopic imaging of porous media to Magnetic Resonance Imaging (MRI) of the human lungs. The SEOP process involves transfer of angular momentum from circularly polarised laser photons to the electrons of an alkali metal vapour. Noble gas nuclei can then be polarised via collisions with the alkali metal vapour. Ultra-low frequency Raman Spectroscopy may be used to perform rotational temperature measurements of a nitrogen buffer gas in these SEOP experiments in real-time, in an attempt to understand the poorly understood and highly complex system dynamics and energy transport processes. The work contained in this thesis aims to investigate the co-dependence of these dynamics, in order to characterise the SEOP process in greater detail for a variety of gas mixtures, temperatures and alkali metal targets. With this, it is hoped that HP noble gases may be produced with greater efficiency, achieving faster build-up rates and higher net magnetisation. In addition to in situ Raman spectroscopy, additional diagnostic techniques were implemented in order to illustrate the co-dependence of variables during the thermal exchange processes present in SEOP. Low-field NMR spectroscopy was utilised to determine the 129Xe net spin polarisation (P_Xe) as a function of time and position within the SEOP vessel, whilst near-infra-red (NIR) optical absorption spectroscopy allowed an estimate of the alkali metal polarisation and global pump laser power absorption to be determined. Additionally, initial studies into the use of optical absorption spectroscopy at various wavelengths for determination of the alkali metal number density are discussed. A chronology of experiments conducted using an `in-line', optically filtered Raman probe arrangement will be presented, culminating in the development of a fully automated, single-axis translational stage to perform rapid measurement of the rotational nitrogen temperature (T_N2) within the optical pumping cell with a high degree of temporal and spatial precision. The automated nature of the system facilitates a >3-fold improvement in the rate of thermal data acquisition, with greater ease and reliability than the previous manual method. In addition to pure rubidium, rotational temperature determination via Raman spectroscopy is demonstrated in a variety of rubidium/caesium hybrid alloy mixtures. In this way it may be possible to more efficiently utilise the greater spin exchange rate of caesium with 129Xe to achieve hybrid Rb/Cs cross-polarisation. The result of this is the first observation of 129Xe polarisation in a hybrid Rb/Cs system exceeding that of an equivalent pure Rb system under otherwise identical experimental conditions.
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Six, Joseph. "New MRI contrast agents through spin exchange optical pumping of noble gases with a nuclear electric quadrupole moment." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14118/.
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Hyperpolarized 83Kr has previously demonstrated MRI contrast that is sensitive to the chemical composition of the surface in a porous model system. One-dimensional nuclear magnetic resonance spectroscopy of hyperpolarized 83Kr has also revealed distinctive longitudinal relaxation times from selected regions of an ex vivo rat lung originating from differences in surface to volume ratio. However, at the time, MRI using longitudinal relaxation for contrast was not attempted due to limited signal intensities. Methodological advances of the spin exchange optical pumping process have led to a substantial increase in the 83Kr hyperpolarization and the resulting signal intensity. This methodology originates from a below-ambient pressure hyperpolarization technique explored and developed in this work. Using the improved methodology for spin exchange optical pumping of isotopically enriched 83Kr has resolved anatomical details of ex vivo rodent lungs using hyperpolarized 83Kr MRI for the first time. Different 83Kr longitudinal relaxation times were found between the main bronchi and the parenchymal regions of the lung. The T1 weighted hyperpolarized 83Kr MRI provided the first demonstration of surface quadrupolar relaxation pulmonary MRI contrast. Novel hyperpolarization techniques of 129Xe have also been explored resulting a study into the combustion process of methane. Using 129Xe as a probe into the combustion process permitted the first in situ MRI of combustion and enabled spatial-velocity profiles.
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Andersen, Diego. "Hybrid organic/inorganic micro-pixellated light-emitting devices based on the optical pumping of organic polymer gain media." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/30919.
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This thesis describes the work carried out under HYPIX, a collaborative research project aimed at developing hybrid organic/inorganic optoelectronic devices, with particular focus given to imaging systems used in the optical pumping of organic polymer gain media. State-of-the-art generations of inorganic light-emitting diodes are presented, along with an overview of the evolution of such devices over the years. A brief outlook is also given on current advances in organic semiconductor gain materials research, as well as laser cavity design. The challenges in designing an optical system capable of pumping organic materials with highly divergent light sources are highlighted, together with the methods that were used to overcome them. Various attempts at optically pumping several organic materials are detailed, highlighting the importance of combining several factors such as energy density, pump spot size and pump pulse duration all at once in order to achieve lasing in this new type of hybrid device. Possible improvements which could in the future lead to the first indirectly electrically pumped organic semiconductor laser are listed. Secondary experiments are also described, covering the proof-of-concept use of computer- controlled, inorganic micro-scale light sources as a spatially-resolving spectrometer for organic polymer targets. A deviation of under 10 % from absorbance values calculated for the samples using a commercial spectrometer is shown.
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Molway, Michael Jhon. "EXPERIMENTAL ADVANCES IN CLINICAL-SCALE PRODUCTION OF HYPERPOLARIZED 129XE AND 131XE VIA STOPPED-FLOW SPIN-EXCHANGE OPTICAL PUMPING." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/theses/2360.
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Spin-exchange optical pumping (SEOP) produces hyperpolarized noble gases (e.g. 129Xe and 131Xe) that have been used to improve spatial resolution and speed of biological magnetic resonance imaging, enhance NMR signals of molecules and materials, and utilized in fundamental physics experiments. In SEOP, circularly polarized laser light optically pumps an alkali metal vapor (e.g. Cs or Rb) into an electronically spin-polarized ground state. This electronic spin polarization can then be transferred to the nucleus of a noble gas during gas phase collisions. Over time, a bulk nuclear spin polarization begins to accumulate, resulting in hyperpolarized (HP) gases. The research presented in this thesis is concerned with the optimization of experimental aspects in clinical-scale HP 129Xe and high-density HP 131Xe production by stopped-flow SEOP—specifically with respect to alkali metal choice, laser technology, SEOP cell design and experimental conditions. This thesis is divided into five main chapters. The first chapter is written to provide an introduction into the field of NMR, giving both historical context and relevant NMR phenomenon to help understand nuclear spin hyperpolarization. The second chapter gives a brief introduction into SEOP and how the evolution of laser technology has given rise to current methodologies. Secondly, this chapter includes a brief summary of SEOP theory as well as mathematically outlines the process of how electron spin polarization via optical pumping leads to long-lived nuclear spin polarizations via spin-exchange. Furthermore, this chapter provides a description of the stopped-flow (i.e. batch-mode) SEOP setup and how in situ measurements of HP noble gases are made. Chapters 3 and 4 are concerned with hyperpolarization of 129Xe and 131Xe, respectively. In both of these chapters, the physical and chemical properties of the respective isotope of xenon are given followed by how to calculate their bulk nuclear spin polarizations using in situ measurements. Exploration to the changes in experimental conditions (i.e. alkali metal choice, temperature, laser technology, etc.) allowed for a comparison of the resulting spin dynamics and polarizations to be made in both chapters. In addition, Chapter 3 includes a brief description of the continuing efforts to implement an aluminum optical pumping cell for use in SEOP. Finally, Chapter 5 will cover preliminary work towards transferring the polarization from HP 129Xe to that of a target molecule. While other groups have shown that this ‘xenon induced polarization’ is possible, we have yet to replicate this phenomenon; However, Chapter 5 will show our work towards ex situ measurements of HP 129Xe and how this will act as a stepping stone towards transferring the polarization to a target molecule.
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Oto, Takao. "Emission Mechanisms in Al-rich AlGaN Quantum Wells toward Deep Ultraviolet Light Emitters by Electron Beam Pumping." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188542.
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Nikolaou, Panayiotis. "SPECTROSCOPIC STUDIES OF NUCLEAR SPINS POLARIZED VIA SPIN EXCHANGE OPTICAL PUMPING AND DYNAMIC COUPLING IN CRYPTOPHANE HOST-GUEST COMPLEXES." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/dissertations/185.
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NMR is a powerful analytical spectroscopic tool used to perform detailed studies of structure and dynamics of molecules in solution. However, despite NMR's excellent spectral sensitivity, most NMR methods suffer from low detection sensitivity. This low detection sensitivity results largely from extremely small (Boltzmann) nuclear spin polarization at thermal equilibrium--in even the strongest of magnets. This dissertation focuses on selected research areas that maybe used to combat the limitations presented by NMR and measure weak spectral responses with atomic-scale precision. In particular, these methods involve the use of laser-polarized xenon, liquid crystals, and polarization transfer (cross-polarization) techniques to enhance NMR sensitivity and/or measure weak interactions. The potential use of these tools to study host-guest interactions is of particular interest. In certain systems the sensitivity problem of conventional NMR/MRI can be overcome by applying optical pumping (OP) methods to enhance nuclear spin polarization. For instance, OP of noble gases (such as xenon) is employed to dramatically increase their nuclear spin polarization by transferring angular momentum of laser light to electronic and then nuclear spins. Next, cryptophane complexes are ideal choices for fundamental studies of prototypical host-guest interactions. Of general interest when studying host-guest interactions is how (1) physical confinement at the nanoscale and (2) interactions between guest and host may affect the properties, dynamics, interactions, and/or reactivity of a trapped molecule and the host/guest complex as a whole. As a more specific example, we are interested in probing host-guest dynamic coupling, which refers to the relative motion of the guest within the host, determined by the relative sizes and geometries--as well as the interactions involved. With the development of new NMR methods and techniques, we hope to gain insight into mechanisms that underlie complex formation by probing the structures, dynamics and energetic contributions involved in ligand binding, where molecular contributions such as: orientational and motional freedom of the guest; and structure, dynamics, and ordering of the host can influence the behavior of inclusion complexes.
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Khastehdel, Fumani Ahmad. "QUANTUM CONFINED STATES AND ROOM TEMPERATURE SPIN COHERENCE IN SEMICONDUCTOR NANOCRYSTAL QUANTUM DOTS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1449151739.
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Andalkar, Amar. "Spontaneous spin polarization and hysteresis in cesium vapor pumped by linearly polarized light : an experimental, theoretical, and computational study /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9734.
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Batz, Marion. "Metastability exchange optical pumping in 3He gas up to 30 mT : efficiency measurements and evidence of laser-induced nuclear relaxation." Paris 6, 2011. http://www.theses.fr/2011PA066214.
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Les progrès en pompage optique (PO) par échange de métastabilité (EM) dans de l’hélium-3 gazeux à forte puissance laser, dont les applications sont variées, mais aussi à forte pression p3 et fort champ magnétique B ont fortement motivé la reprise d’investigations pour comprendre les processus limitant cette technique puissante. Nous présentons une étude systématique, expérimentale et théorique, de l’efficacité du POEM et des mécanismes de relaxation à B≤30 mT et p3=0. 63−2. 45 mbar. La polarisation nucléaire M de l’hélium-3 est mesurée par absorption en configuration longitudinale, en utilisant des faisceaux à 1083 nm de faible puissance, parallèles à B et à l’axe de la cellule, et de polarisations circulaires opposées pour sonder la distribution des populations dans l’état métastable. Nos tests détaillés montrent que cette méthode est fiable pour l’étude de la dynamique du POEM malgré la redistribution des populations par la lumière de pompage. La perte de M associée à l’émission de lumière polarisée par la décharge qui crée le plasma nécessaire au POEM décroît au-dessus de 10 mT, comme attendu, à cause du découplage hyperfin dans les états très excités. Pourtant cela n’améliore pas l’efficacité du POEM à forte puissance laser. Par contre, nous avons mis en évidence une relaxation supplémentaire liée à la présence du laser pompe. Les pertes importantes de M renforcées par PO, qui limitent actuellement les performances du POEM, sont étudiées quantitativement avec une approche basée sur un bilan de moment angulaire et un modèle détaillé, récemment développé, qui décrit les effets combinés du PO, de l’EM et de la relaxation, validé par comparaison aux résultats expérimentaux.
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Zhaksylykova, Indira. "Magneto-optic detection limits for semiconductor spintronics." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX099/document.
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Ce travail explore l'utilisation de l'effet magnéto-optique pour étudier la dynamique de spin des électrons de conduction dans les semi-conducteurs non magnétiques lorsqu'ils sont pompés avec des photons polarisés circulairement. En général, les moments magnétiques hors-équilibre induits optiquement dans les semi-conducteurs non magnétiques sont plus petits que ceux des matériaux magnétiques. L'effet magnéto-optique en principe offre une sensibilité suffisante pour détecter ces faibles moments magnétiques via une mesure de rotation Faraday dans la limite de bruit de photons. Nous avons comparés trois méthodes de détection: les polariseurs partiellement croisés, l’interféromètre de Sagnac et le pont optique. L'interféromètre de Sagnac se révèle fonctionnellement équivalent aux polariseurs partiellement croisés, avec une sensibilité diminuée par la perte de photons à chacun des séparateurs de faisceaux nécessairement présents dans cette configuration expérimentale. Par contre, il a été démontré précédemment que les interféromètres de Sagnac permettent de faire la distinction entre les rotations dites réciproques et non réciproques, et cette thèse propose de nouvelles géométries de Sagnac pour distinguer les rotations en fonction de leurs symétries en temps et en parité. La technique du pont optique présente les meilleures performances. Elle permet une mesure de l'angle de rotation de Faraday limitée par le bruit de photons, même avec des puissances lumineuses importantes reçues par les détecteurs, ce qui permet d'obtenir la meilleure figure de mérite possible. Dans les expériences conduites sur des matériaux magnétiques, un bruit de quelques nrad/√Hz a été mesuré pour une puissance de sonde de 10 mW. Une série de mesures de rotation Faraday pompe-sonde à température ambiante a été réalisée sur GaAs pompé optiquement. Les plus grands signaux sont obtenus lorsque le moment magnétique généré et détecté est maximisé en focalisant fortement les faisceaux pompe et sonde et en choisissant une longueur d'onde de la sonde accordée à une résonance optique dans la structure électronique. Les mesures en champ magnétique transversal montrent un champ Hanle de 0.43 T, à partir duquel on déduit la durée de vie de spin de 88 psThis work explores the use of the magneto-optical Kerr effect to study conduction electron spin dynamics in non-magnetic semiconductors when pumped with circularly polarized photons. Typically, non-equilibrium, optically-induced magnetic moments in non-magnetic semiconductors are orders of magnitude smaller than those of magnetized materials, including both magnetic and non-magnetic materials in an external magnetic field. The magneto-optical Kerr effect in principal offers sufficient sensitivity to detect such small magnetic moment via a measurement of the Faraday rotation angle of a probe beam in the photon shot noise limit. Three detection configurations have been experimentally compared: partially crossed polarizers, a Sagnac interferometer and an optical bridge. The Sagnac interferometer is shown to be functionally equivalent to partially crossed polarizers, although its sensitivity is compromised by lost photons at each of the obligatory beam splitters present in such a geometry. On the other hand, it has previously been shown that Sagnac interferometers can distinguish between so-called reciprocal and non-reciprocal rotations, and this thesis proposes novel Sagnac geometries to distinguish rotations according to their time and parity symmetries. The optical bridge technique allows for a photon-shot noise limited measurement of the Faraday rotation angle, even with large photon intensities on the detectors, thereby yielding the best possible figure-of-merit. In demonstrations on magnetic materials, a noise floor of a few nrad//√Hz was measured for a probe power of 10 mW. A series of room-temperature, pump-probe Faraday rotation measurements is performed on optically pumped GaAs to compare and contrast this method with standard polarized photo-luminescence techniques. The largest signals are found when the locally probed moment is maximized by strongly focusing the pump and probe beams, and by choosing a probe wavelength tuned to an optical resonance in the electronic structure. Measurements in transverse magnetic field show a Hanle field of 0.43 T, from which the spin lifetime of 88 ps is deduced
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Batz, Marion [Verfasser]. "Metastability exchange optical pumping in 3He gas up to 30 mT : efficiency measurements and evidence of laser-induced nuclear relaxation / Marion Batz." Mainz : Universitätsbibliothek Mainz, 2012. http://d-nb.info/1019667877/34.
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JAKUTIS, NETO JONAS. "Low gain Nd:YLF lasers operating in the quasi-three level transition and in Raman lasers." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10200.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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MALDONADO, EDISON P. "Estudo dos mecanismos de geracao de pulsos ultracurtos em lasers de neodimio com bombeamento continuo longitudinal." reponame:Repositório Institucional do IPEN, 1995. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10465.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Whiting, Nicholas. "Using High-Powered, Frequency-Narrowed Lasers For Rb/129Xe and Cs/129Xe Spin-Exchange Optical Pumping To Achieve Improved Production of Highly Spin-Polarized Xenon For Use In Magnetic Resonance Applications." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/dissertations/172.
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Nuclear magnetic resonance (NMR) spectroscopy has been extensively used to investigate numerous systems of interest, ranging from collections of molecules to living organisms. However, NMR suffers from one key drawback: an inherent lack of detection sensitivity, as compared to other common forms of spectroscopy. This is due to the minute nuclear magnetic moments and low nuclear spin polarization levels at thermal equilibrium (~10-5 to 10-6), and thus necessitates the use of relatively large sample volumes. One way to overcome this low detection sensitivity is to introduce a species with highly non-equilibrium nuclear spin polarization, such as `hyperpolarized' xenon-129. Hyperpolarized xenon can either be used as its own chemical sensor (due to its exquisitely sensitive chemical shift range), or the non-equilibrium polarization may be transferred from xenon to another molecule of interest (such as a protein or inclusion complex). Hyperpolarized xenon is produced through a process known as spin-exchange optical pumping (SEOP), where the angular momentum from resonant, circularly-polarized light is transferred to the electronic spins of an alkali-metal, and is subsequently transferred to the xenon nuclei through gas-phase collisions. While SEOP has been extensively characterized throughout the years, new experimental techniques and emerging technologies have considerably advanced the field in recent years, and may enable a new understanding of the underlying physics of the system. The first five chapters in this dissertation review background information and the principal motivations for this work. Chapter one reviews the basics of NMR, from the various components of the nuclear spin Hamiltonian and different spin-relaxation pathways to the reasons behind the low polarization of nuclear spins at thermal equilibrium and a few alternative methods to `boost' the NMR signal. Chapter two discusses the fundamental aspects of SEOP, including the electronic spin polarization of the alkali-metal, polarization transfer to the xenon nuclei, and different avenues for the spin polarization to be depleted. The third chapter covers the practical considerations of SEOP from the viewpoint of an experimentalist; namely, the experimental differences when using a variety of alkali metals and noble gases, as well as different SEOP apparatuses and experimental parameters. Chapter four details a variety of different light sources that may be used for SEOP; specifically, the use of laser diode arrays (LDAs) are reviewed, including LDAs that have been frequency-narrowed for more efficient light absorption by the alkali metal. The fifth background chapter covers a variety of magnetic resonance applications of hyperpolarized xenon, including molecular biosensors, specific and non-specific binding with proteins, materials studies, and in vivo applications. The sixth chapter is used as an overview of the dissertation research, which is presented in chapters seven through eleven. Chapter seven details the arrangement of the particular SEOP apparatus used in this research, as well as the experimental protocol for producing hyperpolarized xenon. The eighth chapter accounts the implementation and characterization of the first frequency-narrowed LDA used in this research, as well as an equal comparison to a traditional broadband LDA. Chapter nine introduces the use of in situ low-field NMR polarimetry, which was used to distinguish an anomalous dependence of the optimal OP cell temperature on the in-cell xenon density; the low-field set-up is also used to examine the build-up of nuclear spin polarization in the OP cell as it occurs. The tenth chapter covers the use of high power, frequency-narrowed light sources that are spectrally tunable independent of laser power; this allows for the study of changes to the optimal spectral offset as a function of in-cell xenon density, OP cell temperature, and laser power. Xenon polarization build-up curves are also studied to determine if the spectral offset of the laser affects the nuclear spin polarization dynamics within the OP cell. Finally, chapter eleven accounts the use of high power, broadband LDAs to perform SEOP in which cesium is used as the alkali metal; these results demonstrate (for the first time) that the xenon polarization generated by cesium optical pumping can surpass that of rubidium OP under conditions of high laser flux and elevated in-cell xenon densities.
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Volchkov, Valentin V. [Verfasser], and Tilman [Akademischer Betreuer] Pfau. "Optical pumping of a dense quantum gas at its limits : continuous Sisyphus cooling and demagnetization cooling towards degeneracy / Valentin V. Volchkov. Betreuer: Tilman Pfau." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1047337258/34.
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Pérez, Ramírez Alexander. "Bombeamento óptico com lasers de 13CO2 : espectroscopia de absorção fotoacústica no infravermelho e de emissão laser no Terahertz." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277205.
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Orientador: Daniel PereiraDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Neste trabalho duas cavidades laser seladas de 13CO2 de diferente capacidade de sintonia (110MHz e 200MHz) foram montadas e caracterizadas para realizar estudos de espectroscopia de absorcção fotoacústica no infravermelho (IV) e de emissão laser no infravermelho longí?nquo (IVL) mediante a técnica de bombeamento óptico de moléculas polares. Utilizamos o modelo molecular vibro-roto-torcional para moléculas tipo metanol para assim entendermos as regras de seleção e de polarização envolvidas no bombeamento óptico para realizar os estudos de espectroscopia fotoacústica e a geração e caracterização de linhas laser IVL. Medidas espectroscópicas de absorção fotoacústica de três isótopos do metanol, na fase gasosa, foram obtidas mediante o bombeamento óptico na banda de emissão 9P do laser de 13CO2 com capacidade de sintonia de 110MHz. Os isótopos utilizados foram o 13CD3OH, CD3OD e o 13CD3OD. Os espectros para o 13CD3OD são obtidos, até onde sabemos, pela primeira vez. Obtivemos um total de 36 espectros de absorção fotoacústica os quais serviram de orientação para conseguirmos, com o bombeamento destas moléculas, a geração de 7 linhas laser IVL, que foram caracterizadas quanto ao seu comprimento de onda, sua dessintonia, pressão ideal de operacão, polaridade e intensidade relativas. Duas destas linhas obtidas são linhas novas. Já, os dados de polarização relativa e de dessintonia são novos, mesmo para as linhas já conhecidas
Abstract: In this work two 13CO2 sealed-off lasers cavities with different tuning range (110 MHz and 200MHz) were mounted and characterized to realize spectroscopy studies of infrared photoacoustic absorption and of far infrared (FIR) laser emission by the optical pumping technique of polar molecules. We used the vibra-roto-torsional molecular model for like methanol molecules to understand the selection and polarization rules involved in the optical pumping to achieve the photoacoustic spectroscopic and the generation and characterization of FIR laser lines. Spectroscopic measurements of photoacoustic absorption for three methanol isotopes, in gas phase, were obtained by the optical pumping with the 9P band of the 13CO2 laser with 110MHz of tuning range. The isotopes used were 13CD3OH ,CD3OD e o 13CD3OD. The spectrums for the 13CD3OD are obtained, to our knowledge, by the first time. We have obtained a total of 36 photoacoustic absorption spectra which served as a guide to succeed, by the pumping of these molecules, generation of 7 FIR laser lines, which were characterized according to its wavelength, its offset, ideal pressure of operation, polarity and relative intensity. Two of these lines obtained are new lines. The relative polarization and offset data are new, even for the already known lines
Mestrado
Física Atômica e Molecular
Mestre em Física
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Wolber, Jan. "Hyperpolarized 129Xe as an NMR probe for functional studies." Thesis, Institute of Cancer Research (University Of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341895.
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Hughes, Alison Frances. "A new theory of lasers with application to photonic band gap materials." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368127.
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Ngcobo, Sandile. "Short-pulse generation in a diode-end-pumped solid-state laser." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4225.
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Thesis (MSc (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: This thesis consists of two parts; the first part is a discussion on the detailed history of the development of different types of modelocked lasers, especially the neodymium-doped lasers. The second part describes the design and development of a modelocked diode-end-pumped solid state Nd:YVO4 laser using Semiconductor Saturable Absorbers. The first part of this work will cover the history of modelocking where different types of lasers were used to generate ultrashort pulses. The discussion will mainly focus on neodymium-doped lasers such as Nd:YVO4, where we will look at the spectral properties such as energy levels, absorption and emission wavelengths of such a laser. The discussion will also look at different types of optical pump sources; such as diode lasers and flashlamps, where we will see the advantages of using diode lasers as pump sources due to their better operating conditions and efficiency. We will also look at two different types of diode pumping setup schemes, which are end-pumping and side pumping; where we will discover that diode-end-pumping is a better scheme for laser mode matching resulting in high efficiency and very good beam quality when compared to side pumping. The gain bandwidth of the laser material will also be discussed showing that a laser material with a very large gain bandwidth and broad emission bandwidth is suitable for generating ultrashort pulses, such as Ti:Sapphire crystal. The discussion will also cover ultrafast lasers that have a small amplification bandwidth suitable for diode-end-pumping and that produce high average output power. Ultrafast lasers with low amplification bandwidth such as Nd:YAG and Nd:YVO4 will be discussed showing that they can generate very short pulses with durations of down to 19 ps and 20 ps respectively and average output powers of 27 W and 20 W. The technique of creating ultrashort pulses which is called modelocking will be discussed, where passive modelocking will be shown to be more suitable for creating ultra short pulses in the femtosecond region and active modelocking in the picosecond region. The discussion will also cover saturable absorbers for passive modelocking where we will discuss the use of semiconductor saturable absorber mirrors to generate reliable self starting modelocked pulses. We will also cover the instabilities associated with using saturable absorbers where we will discuss different methods for reducing the instabilities by using gain media with the smallest saturation fluence. The second part of the work will deal with the design and development of SESAM modelocked diode-end-pumped Nd:YVO4 lasers. This part will include a discussion on the resonator design criteria’s for achieving a stable modelocked diode-end-pumped solid-state laser. The choice of using Nd:YVO4 as a gain medium will be shown to be influenced by its large cross sectional area, which is useful in increasing the gain bandwidth for possible ultrashort pulse generation. The resonator for high power continuous wave (cw) output has been designed using simulation software developed at St Andrews University. We will also discuss stability criteria such as the laser spot size inside the crystal and on the end mirror and how they can be incorporated into the resonator design software. The discussion will also include the pump setup design and the efficient cooling method of the crystal using a copper heat sink. The methodology of obtaining stable, thermal lens invariant, single transverse mode operation during power scaling of Nd:YVO4 lasers will be discussed. A lens relay approach is used to extend the cavity length so as to introduce spot size control in the designed diode-end-pumped Nd:YVO4 laser that will be shown to produce a maximum average output power of 10.5 W with an average beam quality factor M2 of 1.5. We will also discuss the incorporation of a single quantum well SESAM within the extended diode-end-pumped Nd:YVO4 laser resulting in cw-modelocked pulses at an average output power of 2.8 W with pulse repetition frequency of 179 MHz, equivalent to the cavity round trip time of 5.6 ns. The incorporation of the double quantum well SESAM will also be shown to produce stable Q-switched modelocked pulses at an average output power of 2.7 W with pulse repetition frequency of 208 KHz.
AFRIKAANSE OPSOMMING : Hierdie tesis bestaan uit twee dele. Deel 1 is ‘n indiepte bespreking rondom die ontwikkelingsgeskiedenis van Modusgebonde lasers, veral van Neodemiumdoteerde lasers. Deel 2 beskryf die ontwerp en ontwikkeling van ‘n Modusgebonde diodeentgepompde vastetoestand Nd:YVO4 laser deur van ‘n Halfgeleier Versadigbare Absorbeerder (SESAM) gebruik te maak. Die eerste afdeling fokus op Modusbinding om ultrakort pulse te ontwikkel in verskillende tipes lasers. Die bespreking sentreer rondom Neodemiumdoteerde lasers soos Nd:YVO4. In hierdie geval beskou ons ook die spektraaleienskappe van die laser vir beide die absorpsie en emissie golflengtes. Verder word verkillende tipes pompbronne ondersoek (soos diodelasers en flitslampe). Die voordele van diodelasers kom sterk na vore a.g.v. beter werking en effektiwiteit. Verskillende pompopstellings word ook ondersoek naamlik ent-en kantpomping. Entpomping kom hier na vore as die beter opsie i.t.v. laser-moduspassing. Dit lei tot ‘n hoër effektiwiteit wat ‘n beter straalkwaliteit tot gevolg het, in vergelyking met kantgepompde opstellings. Die versterkingsbandwydte word ook bespreek: ‘n groot versterkingsbandwydte en breë emissiebandwydte is geskik om ultrakort pulse te ontwikkel. Ti:Saffier is ‘n goeie voorbeeld. Ultravinnige lasers met ‘n klein versterkingsbandwydte word ook bespreek aangesien dit geskik is vir diodeentpomping wat dan ‘n hoë gemiddelde uitsetdrywing lewer. Nd:YAG en Nd:YVO4 word ondersoek en daar word getoon dat hul pulse van so kort as 19 ps en 20 ps onderskeidelik teen ‘n gemiddelde uitsetdrywing van 27 W en 20 W kan lewer. Die tegniek waarmee ultrakort pulse geskep word is Modusbinding: passiewe modusbinding is meer geskik vir femtosekonde pulse en aktiewe modusbinding is meer geskik vir pikosekonde pulse. Verder word versadigbare absorbeerders bespreek, vir hul gebruik in die betroubare selfinisiërende modusgebonde pulse. Die onstabiliteite geassosieer met versadigbare absorbeerders word ook bespreek asook verskillende metodes om dit te minimaliseer. Die tweede afdeling behandel die ontwerp en ontwikkeling van ‘n SESAM modusgebonde diode-entgepompde Nd:YVO4 laser. Die resonator ontwerpspesifikasies vir stabiele werking word ook bespreek. Die keuse van Nd:YVO4 as versterkingsmedium is a.g.v. die groot deursnitarea wat die versterkingsbandwydte verhoog, om ultrakort pulse te genereer. Die resonator vir hoë drywing kontinuestraal werking is ontwerp deur van St Andrews sagteware gebruik te maak. ‘n Bespreking van stabiliteitsspesifikasies soos die laser kolgrootte, binne die kristal asook op die entspieël volg, asook die pompmetodiek en effektiewe verkoeling van die kristal. Die totale metodiek rondom die verkryging van ‘n stabiele, termieselens invariante, enkele transversale modus laser word bespreek met die oog op drywingsverhoging. Die geval onder bespreking is waar die laser se kolgrootte beheer kan word op die entspieël deur die resonatorlengte aan te pas. Dit word getoon dat dit ‘n kontinuestraal laser van 10.5 W drywing kan lewer teen die maksimum gemiddelde straalkwaliteit van M2 = 1.5. Die byvoeging van ‘n enkele kwantumput SESAM in die laser het modusgebonde pulse tot gevolg. Die gemete waardes was 2.8 W gemiddelde drywing met ‘n pulsherhalingstempo van 179 MHz wat in lyn is met die pulsbewegingstyd in die resonator van 5.6 ns. Deur van ‘n dubbele kwantumput SESAM gebruik te maak word Q-geskakelde modusgebonde pulse verkry, teen ‘n gemiddelde uitsetdrywing van 2.7 W en ‘n pulsherhalingstempo van 208 KHz.
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ROSSI, WAGNER de. "Construcao e operacao de lasers de neodimio: estudo do comportamento temporal." reponame:Repositório Institucional do IPEN, 1995. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10435.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Currey, Ronnie. "Investigation of Specialized Laser and Optical Techniques to Improve Precision Atomic Spectroscopy of Helium." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1703412/.
Full textAbstract:
The aim of this thesis is to develop both Yb and Tm fiber laser sources with all fiber cavities. Both wavelength ranges provide useful laser sources for optical pumping of helium. The goal is to develop Tm laser sources operating at 2058 nm to optically quench 3He (2058.63 nm) and 4He (2058.69 nm) singlets (21S0). We also have developed Yb laser sources at 1083 nm to optical pump the triplet states of helium and laser cool an atomic beam of helium.
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Ferreira, João Carlos de Melo. "Fiber amplifiers in transparent and dynamic optical networks." Doctoral thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/14090.
Full textAbstract:
Doutoramento em Engenharia EletrotécnicaIn this thesis a study of optical fiber amplifiers in the context of transparent and dynamic optical networks is performed. We propose and validate a simplified model to estimate the gain profile and amplified spontaneous emission (ASE) noise of broadband counterpumped Raman fiber amplifiers (RFAs). The proposed model requires very low computational resources and it is suitable to be used in network planning tools. Based on the proposed model, we also present an algorithm to design flat gain counter-pumped RFAs for the extended C-band with low computational requirements. We experimentally verify that the pump-reflecting RFA presents a higher transient response due to channels add/drop, when compared to the conventional counter-pumped RFA. This makes this amplifier configuration unsuitable for transparent and dynamic optical networks. To mitigate the transient response due to channel add/drop, a pumpcontrolled gain-locked system based on the monitorization of the reflected pump power is proposed and validated numerically and experimentally. Following this approach, an efficient low-cost RFA suitable for dynamic optical networks is proposed. The dependence of the dynamical response of erbium-doped fiber amplifiers (EDFAs) on the pump wavelength, pump power, and temperature due to spectral hole burning (SHB) and site dependent pumping (SDP) is experimentally investigated. A dependence of the dynamic response on the pump wavelength, for amplifiers pumped around 1480 nm, is shown. In order to explain this dependence, the impact of SDP on the performance of EDFAs pumped at wavelengths around 1480 nm is investigated, both experimentally and numerically. As a result, an improved model incorporating the SDP effect for twolevel EDFAs is derived and experimentally validated.
Nesta tese é feito um estudo sobre amplificadores de fibra ótica no contexto de redes óticas transparentes e dinâmicas. Propomos e validamos um modelo simplificado para estimar o perfil do ganho e do ruído de emissão espontânea amplificada (ASE), para amplificadores de Raman (RFAs) contra propagantes. O modelo proposto requer baixos recursos computacionais e é adequado para ser usado em ferramentas de planeamento da rede. Com base no modelo proposto, apresentamos também um algoritmo com requisitos computacionais baixos para desenhar RFAs contra propagantes com ganho constante para a banda C estendida. Verificamos experimentalmente que um RFA contra propagante com reflexo da potência da bomba devido à adição/remoção de canais apresenta uma resposta transiente mais elevada, quando comparado com um RFA contra propagante convencional. Isto torna esta configuração inadequada para redes óticas transparentes e dinâmicas. Para mitigar a resposta transitória devido à adição/remoção de canais, um sistema de controlo do ganho baseado na monitorização da potência da bomba refletida é proposto e validado numérica e experimentalmente. Seguindo esta abordagem, um RFA contra propagante eficiente e de baixo custo adequado para redes óticas dinâmicas é proposto. A dependência da resposta dinâmica dos amplificadores de fibra dopada com érbio (EDFAs) em função do comprimento de onda da bomba, da potência da bomba e da temperatura devido ao spectral hole burning (SHB) e site dependent pumping (SDP) é investigada experimentalmente. Nos resultados obtidos é mostrada a dependência da resposta dinâmica em função do comprimento de onda da bomba, para amplificadores bombeados em torno de 1480 nm. Para explicar esta dependência, o impacto do SDP no desempenho de EDFAs bombeados em comprimentos de onda em torno de 1480 nm é investigado, tanto experimental como numericamente. Como resultado, um modelo mais completo, incorporando o efeito SDP para EDFAs de dois níveis é derivado e validado experimentalmente.
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Tsiminis, Georgios. "One- and two-photon pumped organic semiconductor lasers." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/927.
Full textAbstract:
This thesis describes a number of studies on organic semiconductors focused around using them as gain media for lasers. The photophysical properties of organic semiconductors are studied using a wide range of experimental techniques, allowing the evaluation of new materials and novel excitation schemes for use in organic semiconductor lasers. Polyfluorene is a well-established conjugated polymer laser gain medium and in this thesis its excellent lasing properties are combined with its two photon absorption properties to demonstrate a tunable two-photon pumped solid-state laser based on a commercially available organic semiconductor. A family of bisfluorene dendrimers was studied using a number of photophysical techniques to evaluate their potential as laser materials. Distributed feedback lasers based on one of the dendrimers are demonstrated with lasing thresholds comparable to polyfluorene. The same materials were found to have enhanced two-photon absorption properties in comparison to polyfluorene, leading to the fabrication of tunable two-photon pumped dendrimer lasers. A member of a novel family of star-shaped oligofluorene truxenes was evaluated as a laser gain material and the distributed feedback lasers made from them show some of the lowest lasing thresholds reported for organic semiconductors, partly as a consequence of exceptionally low waveguide losses in comparison to other single-material thin films. Finally, an organic laser dye is blended with a conjugated polymer, where the dye molecules harvest the excitation light of a GaN laser diode and transfer its energy to the polymer molecules. This is the first time such a scheme is used in an organic laser and in combination with a novel surface-emitting distributed Bragg reflector resonator allows the demonstration of a diode-pumped organic laser, a significant step towards simplifying organic lasers.
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Slaughter, Daniel Stephen, and d. slaughter@aip org au. "Superelastic Electron Scattering from Caesium." Flinders University. Chemistry Physics and Earth Sciences, 2007. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20071009.100421.
Full textAbstract:
This thesis describes an experimental study of superelastic electron scattering from
the 6^2P_3/2
state of caesium. The present status of electron-atom collision studies is
initially reviewed and the motivation behind the current work is then presented. A
description of the theoretical framework is subsequently provided in the context of
the present experimental study, followed by an overview of the several theoretical
approaches for describing electron-atom interactions which are currently available.
The apparatus and experimental setup used throughout the project are also described
in detail. Technical specifications and data are provided, including diagrams (where
appropriate) for a laser frequency locking system, electron gun and spectrometer,
atomic beam source and data acquisition system. The experimental procedures are
explained and discussed, including a detailed analysis of the optical pumping
process required to excite the atomic target. A substantial component of this project
was to address several potential sources of systematic error and to reduce these
wherever possible. All of the errors and uncertainties relevant to the experiment are
discussed in chapter 5.
In chapter 6 the results of the present superelastic electron scattering experiments are
reported for incident electron energies of 5.5eV, 8.5eV and 13.5eV, corresponding
to superelastic electron energies of 7eV, 10eV and 15eV. These results are presented
as three reduced Stokes parameters, P1, P2, P3 and a coherence parameter, P+ . For
comparison, predictions from a number of currently available theories are presented alongside the experimental results. Finally, conclusions are drawn on this work in the context of the current status of electron-atom scattering from alkali-metals.
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Beato, François. "Quelques résultats théoriques et expérimentaux sur les magnétomètres très bas bruit basés sur le pompage optique de l'hélium 4." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY065.
Full textAbstract:
Nous présentons une étude détaillée des magnétomètres hélium 4 à pompage optique en alignement. Ces capteurs fonctionnent intrinsèquement dans un régime de champ magnétique faible (B≲150 nT), mais leur gamme de fonctionnement peut être grandement étendue en utilisant une boucle de compensation du champ.En réutilisant les théories du pompage optique et de l’atome habillé développées dans les années 60, nous obtenons les expressions détaillées des signaux optiques de nos magnétomètres pour les trois raies D_0, D_1 et D_2. Nous étudions ainsi les différentes architectures de capteurs qui peuvent être réalisées, en prenant soin de détailler les deux modes de mesure permis par l’alignement (absorption et biréfringence linéaire). Nous mettons ainsi en avant des nouvelles architectures innovantes des magnétomètres à effet Hanle, en faisant notamment apparaître la possibilité de réaliser une mesure avec un seul accès optique. Nous détaillons également l’étude des magnétomètres à résonance paramétrique dans les deux configurations de mesure permises par l’alignement. Systématiquement nous appuyons nos résultats théoriques via des validations expérimentales.Enfin nous détaillons les sources intrinsèques d’imperfections (effet indésirable du faisceau sonde, light-shift …) et de bruits des capteurs. Cela nous permet de mettre en avant les points forts et faibles des architectures, ainsi que d’étudier leurs performances en terme de sensibilitéThis work presents a detailed study of helium 4 optically pumped magnetometers based on atomic alignment. Although their physical behavior is restricted to low magnetic fields (B≲150 nT), the dynamic range of such sensors may easily be extended using a back action loop on the magnetic field.We explicitly derive analytic expressions of the optical signals of helium magnetometers based on atomic alignment for the three atomic transitions D_0, D_1 et D_2. Doing so we are able to specifically study the different sensor architectures possible. We carefully present the two different ways of measuring a signal using atomic alignment: absorption and linear birefringence. We highlight new architectures of Hanle magnetometers, notably the possibility of measuring a field with one only optical access. We take a particular interest also in parametric resonance magnetometers to write their driving equations either in absorption and birefringence. We systematically complete our theoretical studies with experimental verifications.We finish by studying the intrinsic sources of imperfections (pumping of the probe beam, light-shift …) and noise of the sensors. Thus we discuss pros and cons of the architectures and analyze their theoretical sensitivity
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Hollingworth, Andrew Roy. "Semiconductor optoelectronic infrared spectroscopy." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/842674/.
Full textAbstract:
We use spectroscopy to study infrared optoelectronic inter and intraband semiconductor carrier dynamics. The overall aim of this thesis was to study both III-V and Pb chalcogenide material systems in order to show their future potential use in infrared emitters. The effects of bandstructure engineering have been studied in the output characteristics of mid-IR III-V laser diodes to show which processes (defects, radiative, Auger and phonon) dominate and whether non-radiative processes can be suppressed. A new three-beam pump probe experiment was used to investigate interband recombination directly in passive materials. Experiments on PbSe and theory for non-parabolic near-mirror bands and non-degenerate statistics were in good agreement. Comparisons with HgCdTe showed a reduction in the Auger coefficient of 1-2 orders of magnitude in the PbSe. Using Landau confinement to model spatial confinement in quantum dots (QDs) "phonon bottlenecking" was studied. The results obtained from pump probe and cyclotron resonance saturation measurements showed a clear suppression in the cooling of carriers when Landau level separation was not resonant with LO phonon energy. When a bulk laser diode was placed in a magnetic field to produce a quasi quantum wire device the resulting enhanced differential gain and reduced Auger recombination lowered Ith by 30%. This result showed many peaks in the light output which occurred when the LO phonon energy was a multiple of the Landau level separation. This showed for the first time evidence of the phonon bottleneck in a working laser device. A new technique called time resolved optically detected cyclotron resonance, was used as a precursor to finding the earner dynamics within a spatially confined quantum dot. By moving to the case of a spatial QD using an optically detected intraband resonance it was possible to measure the energy separation interband levels and conduction and valence sublevels within the dot simultaneously. Furthermore this technique has been shown that the inhomogeneous broadening of the photoluminescence spectrum is not purely affected by just size and composition. We suggest that other processes such as state occupancy, In roughing, and exciton binding energies may account for the extra energy.