Dissertations / Theses on the topic 'Emitters'
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Johnson, Eric (Eric M. ). "Self-installation of drip irrigation emitters for prototype emitter testing." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105700.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (page 31).
In this thesis, I tested methods of adhering factory-made drip emitters to the interior of short segments of piping. Different types of adhesive and pipe material combinations were tested, and I selected three combinations for further testing. Performance similar to factory-installed drip emitters was achieved at low pressure, but the necessary watertight seals repeatedly burst at higher water pressures. Alterations to the drip emitter and installation procedure are recommended to increase reliability and resilience of the installation.
by Eric Johnson.
S.B.
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Culham, Stacey. "Polymetallic triplet emitters." Thesis, Northumbria University, 2013. http://nrl.northumbria.ac.uk/36124/.
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This work is concerned with the synthesis and property investigation of a relatively new class of cyclometallated Ir(III) and Pt(II) complexes in which two metal centres are coordinated to a common heterocycle resulting in a rigid polymetallic assembly. Highly luminescent materials which can emit and absorb in a red region of the spectrum were targeted. There are three main parts of the thesis. The first part investigates how luminescent properties of the diplatinum systems are affected by the bridging ligand. A series of novel mono- and dinuclear Pt(II) complexes has been prepared and their luminescent and redox properties investigated. The main observation is that the introduction of the second metal centre leads to a substantial red-shift in absorption and emission. In the second part the role of changing the ligand substituents in a cyclometallated complex has been investigated to determine the extent to which luminescence is affected by the nature of the substituents. A series of mono- and dinuclear Pt(II) complexes have been prepared using substituted pyrazine bridging ligands. It was found that electron donating substituents such as –OMe in the benzene cyclometallating ring cause a red-shift, while electron withdrawing substituents such as –F cause a blue-shift in emission. The final part of the work describes the synthesis of cyclometallated homometallic bis Ir(III) complexes. A series of bis- Ir(III) complexes have been prepared using a terdentate cyclometallating N^C^N coordinating 1,3-di(2-pyridyl)benzene derivative as an auxiliary ligand. It was found that the nature of the bridging ligand determines the overall stability of the complex. Pyrimidine-linked systems were found to be the most stable, while pyrazine analogues readily photodecompose/isomerise. Pyridazine-linked systems lead to ionic complexes where one chloride ligand is shared by two Iridium metal centres.
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Bates, R. "Silicon heterostructure intersubband emitters." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596474.
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It is believed that the Silicon Germanium (SiGe) materials system offers numerous benefits over GaAs/AlGaAs for operation within the THz gap - absorption coefficients are lower due to the non-polar nature of the SiGe lattice and the potential for integration with Si chips exists. Furthermore, operating within the valence band allows surface normal emission to be observed and vertical cavity surface emitting lasers to be fabricated using transitions between light (LH) and heavy (HH) hole subbands and poly-Si/silicon dioxide Bragg reflectors. This dissertation reports upon recent advances made in FIR Quantum Cascade Emitters (QCEs) based within the SiGe materials system. Initial measurements were designed purely to demonstrate the ability of the vertical intersubband transition to absorb radiation. Such structures were also observed to emit and spectroscopy was performed allowing the origin of such emission to be verified as being due to intersubband transitions. QCEs were then designed and processed, allowing the observation of the first surface-normal emission from a QCE in the absence of a grating to be observed. Further designs demonstrated the primary dependence upon the strain within the quantum wells of the energy of the LH1-HH1 transition. The scalability of the active regions has also been demonstrated - the strain symmeterised growth allowing hundreds of layers to be grown at a uniformly high standard. A shift from vertical (intrawell) to diagonal (interwell) transitions using photon assisted tunnelling lead to the theoretical observation of population inversion within the system. One of the key requirements for lasing, the existence of population inversion demonstrates both the potential and feasibility for a QCL to be fabricated in SiGe.
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Mahlmeister, Nathan Howard. "Graphene based thermal emitters." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/24326.
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Mid-Infrared thermal emission sources based on graphene were investigated both experimentally and simulated using the finite element method modelling software package COMSOL. Devices were fabricated by transferring graphene onto various substrates. The thermal emission of few-layer and single graphene on SiO2/Si, under a pulsed square wave drive current, was characterised using spatially resolved thermal emission measurements. It was determined that the devices with single-layer graphene maintained characteristic properties of graphene, while few-layer graphene displayed properties typical of a semi-metal. The effect of thermal management on the emission was investigated by comparing simulations to the emission from these devices and a hexagonal boron nitride encapsulated few-layer graphene device. Limiting the vertical heat dissipation was shown to improve device modulation speed. The emission from the graphene devices was determined to be grey-body in nature. Metamaterial structures, including ring resonators and split ring resonators, were integrated with the encapsulated devices in order to narrow the emission spectra. The emission and reflectance of the devices was characterised using Fourier transform infrared spectroscopy. A tuneable electromagnetically induced transparency like spectral response was observed for devices with metamaterial structures. The resonance peaks were shifted by altering the unit cell parameters. Finally, gallium nitride nano-rod arrays were investigated for the potential to incorporate both spectral control and thermal management into the underlying substrate, in addition to the possibility of the optical generation of graphene plasmons. It was determined that the conventional wet transfer technique was inadequate to transfer the graphene onto the nano-rods. Therefore, a modified transfer technique was utilised, with a significant improvement in the graphene coverage observed. Optical characterisation of the nano-rods using Fourier transform infrared reflectance spectroscopy indicated the excitation of localised surface phonon polaritons, while no evidence was observed in the graphene reflectance spectra of the generation of graphene plasmons.
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Taminiau, Tim Hugo. "Optical antennas for single emitters." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/132097.
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The interaction of light with matter is a central topic in both fundamental science and applied technology. At the heart of this interaction lies the absorption or emission of a photon by an electronic transition in for example an atom, molecule or semiconductor. Because such quantum emitters are generally much smaller than the wavelength of light, they interact slowly and omnidirectionally with light, limiting their absorption and emission.
At radio frequencies similar issues were encountered and addressed long ago. Electrical circuits radiate little because they are much smaller than the corresponding wavelength. To enable wireless communication, they are connected to antennas that have dimensions in the order of the wavelength. These antennas are designed to effectively convert electrical signals into radiation and vice versa. The same concept can be applied in optics.
The central idea of this thesis is that the interaction of a quantum emitter with light can be improved by near-field coupling it to the resonant plasmon modes of a metal nano-particle, which then acts as an optical antenna. In this way, excitation and emission rates can be enhanced, and the angular, polarization, and spectral dependence controlled. Chapter 1 of this thesis outlines these concepts and introduces optical antennas for single emitters.
The experimental demonstration of optical antennas requires the near-field coupling of a single emitter to a resonant optical antenna. We fabricated optical monopole antennas on scanning probes, so that they can be precisely positioned near single fluorescent molecules. In this way we directly mapped the changes in the excitation and emission of a single quantum emitter as it is scanned near the antenna.
Chapter 2 presents the results for the excitation part of the interaction. The enhanced excitation field at the antenna is highly confined (within 25 nm); the emitter only interacts with the antenna mode over this short distance. The antenna resonances were probed directly in the near-field and show that the antenna is indeed an optical analog of a monopole antenna.
The experiments in Chapter 3 demonstrate how the antenna controls the emission. If the emitter is placed at the right position and if the antenna is tuned to resonance, the angular emission of the coupled system is determined by the antenna mode, regardless of the orientation of the emitter. In Chapter 4, we exploit that fact. We demonstrate, theoretically and experimentally, that the radiation from a single emitter coupled to a multi-element optical Yagi-Uda antenna is highly directed. We show that by reciprocity such a high directivity both enhances the excitation field and the collection efficiency.
An intuitive way to understand optical antennas is as cavities for surface plasmon polaritons. In chapter 5, I present an extended description of the interaction of dipolar emitters with radiation through nano-rod antenna modes, by treating the antenna as a cavity. The results demonstrate how the properties of the antenna modes evolve from macroscopic perfectly conducting antennas to nanoscale plasmonic antennas, and highlight the similarities and differences between optical and conventional antennas.
The results presented in this thesis show that optical antennas provide a new way to link single emitters to light. By designing the antenna the absorption and emission properties of the emitter can be tailored. More generally, optical antennas enhance and control light-matter interaction on the nano-scale, making them promising tools for applications in topics as diverse as high resolution near-field scanning optical microscopy, non-linear optics and spectroscopy, and photovoltaic devices.La interacción entre luz y materia es fundamental tanto en ciencia básica como en tecnología aplicada. En el corazón de esta interacción están la emisión y absorción de fotones en transiciones electrónicas de, por ejemplo, átomos, moléculas o semiconductores. Tales emisores cuánticos son más pequeños que la longitud de onda de la radiación con la que interaccionan. La interacción es entonces lenta y omnidireccional, lo que limita los procesos de absorción y emisión. En radio frecuencias este mismo problema fue resuelto tiempo atrás. Los circuitos eléctricos radián poco por ser más pequeños que las ondas de radio. La comunicación inalámbrica es posible sólo si los circuitos están conectados a antenas con dimensiones del orden de la longitud de onda. Las antenas son diseñadas para convertir efectivamente señales eléctricas en radiación y viceversa. Este principio se extender a la óptica. La idea central de esta tesis es que la interacción entre la luz y un emisor cuántico incrementa cuando éste es acoplando, en el campo cercano, a los modos plasmónicos resonantes de una nano-partícula metálica. La partícula actúa entonces como una antena óptica. Es posible entonces aumentar las tasas de excitación y emisión, y controlar la dependencia angular, espectral y en polarización. El capítulo 1 de ésta tesis explica estos conceptos e introduce las antenas ópticas para emisores individuales. Para implementar experimentalmente una antena óptica es necesario acoplar en campo cercano un emisor individual a una antena resonante. Como las antenas ópticas monopolares fueron fabricadas sobre sondas de barrido, podemos ubicarlas con precisión cerca a una molécula fluorescente. Es así como escaneando un emisor cuántico singular cerca a la antena es posible mapear los cambios en la excitación y la emisión. El capítulo 2 presenta los resultados relativos a la parte de la interacción correspondiente a la excitación. El campo excitado en la antena está altamente confinado (25 nm); el emisor solo interactúa con los modos de la antena dentro de esta pequeña región. Las resonancias, probadas directamente en el campo cercano, muestran que en efecto la antena es el análogo óptico a una antena monopolar. Los experimentos en el capítulo 3 muestran como la antena controla la emisión. Cuando el emisor se ubica en la posición correcta y la antena está en resonancia, la emisión del sistema acoplado es determinada por el modo de la antena, independientemente de la dirección del emisor. El capítulo 4 explora esta característica. Teórica y experimentalmente, hemos demostrado la alta direccionalidad de la radiación de un emisor individual cuando es acoplado a una antena Yagi-Uda de múltiples elementos. Por reciprocidad, esta direccionalidad incrementa tanto el campo de excitación como la eficiencia de acoplamiento. En una forma intuitiva las antenas ópticas se pueden entender como cavidades para los plasmones-polaritones de superficie. Tratando las antenas como cavidades, el capítulo 5 presenta una descripción de la interacción entre los emisores dipolares y la radiación mediada por los modos de las nano-antenas. Los resultados muestran como las propiedades de estos modos evolucionan desde las antenas macroscópicas perfectamente conductoras hasta las nano-antenas plasmónicas. Los resultados también explican las diferencias entre las antenas ópticas y las convencionales. Los resultados presentados en esta tesis prueban que las antenas ópticas son una nueva alternativa para acoplar luz a emisores cuánticos individuales. Las propiedades de absorción y emisión del emisor pueden ser controladas diseñando adecuadamente las antenas. Las antenas ópticas permiten amplificar y controlar la interacción entre radiación y materia en la escala nanométrica, convirtiéndolas en herramientas importantes en campos muy diversos. Por ejemplo, en microscopia óptica de campo cercano, en información cuántica, en óptica no lineal, en espectroscopia y en dispositivos fotovoltaicos
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Geiß, Barbara. "Donor-Acceptor Substituted Triplet Emitters." kostenfrei, 2009. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/3972/.
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Krishnan, Jagadamma Lethy. "Characterisation of nanostructured light emitters." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=17192.
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Group III-nitride semiconductors are the dominant inorganic solid state light emitting materials, spanning the UV to infra-red spectral range. InGaN/GaN based LEDs and lasers are commercially available and intense research is being pursued to improve their efficiency. One practical approach is the development of functionalised and/or improved materials patterned on a nanometre length scale. This thesis presents the optical, morphological and compositional characterisation of III-nitride based nanostructured light emitters. The III-nitride nanostructures studied are GaN coalesced above arrays of either nanopyramids or nanocolumns, semipolar and nonpolar InGaN QWs on the facets of GaN nanopyramids, and thin epilayers of AlInN and AlInGaN. Spatially resolved optical characterisation of nano-ELOG GaN layers revealed a shift in the exciton-related band edge emission across the coalesced layer. This is related to Si doping and to strain effects. Study of the semipolar {1011} InGaN QWs grown on the facets of GaN nanopyramids identified a blue shift in QW emission energy as the sampled region is moved up the pyramid facets. This shift is found to follow the release of the tensile strain towards the top of nanopyramid. Luminescence properties of nearly lattice matched AlInN epilayers investigated using CL, PL and PLE spectroscopic techniques revealed that the emission and bandgap energy of the AlInN layers are at higher energy than that of GaN. Results obtained from polarisation resolved PL measurements of AlInN epilayers point to two possible implications: the observed higher energy AlInN emission is either related to defects or this emission is due to carrier recombination occurring in InN clusters similar to those of InGaN epilayers. Optical properties of thin AlInGaN epilayers investigated using PL and PLE spectroscopy revealed a redshift in bandgap energy with increase in InN fraction. The observed spatial intensity fluctuations are discussed in terms of the InN compositional fluctuations and inhomogeneous strain effects.
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Gant, Dean Alan. "Comparison of alkali ion emitters." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28043.
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Natrella, M. "Photonic terahertz emitters and receivers." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1470214/.
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The research work presented in this thesis is concerned with the design, fabrication and characterisation of Continuous Wave (CW) Photonic Terahertz (THz) Emitters employing antenna-integrated Uni-Travelling-Carrier Photodiodes (UTC-PDs), based on the Indium Phosphide (InP) materials system. The solution employing photonic techniques for the generation of sub-millimetre and THz waves, via photomixing of lasers operating at 1550 nm, is a major candidate for the realisation of tuneable, power efficient, compact and cost effective THz sources operating at room temperature. The availability of sources endowed with such properties would make many important applications possible in this frequency range, such as ultra broad band wireless communications, spectroscopic sensing and THz imaging. The UTC-PDs enable high optical to electrical (O-E) conversion efficiency and are key components for the realisation of a photonic terahertz emitter. In this thesis the fabrication and characterisation of test vertically illuminated UTC-PDs, achieved using materials grown by Solid Source Molecular Beam Epitaxy at UCL and the fabrication of high performance waveguide UTC-PDs are reported, as milestones towards the development of a simple, repeatable and high yield fabrication process. A comprehensive study of UTC-PD impedance and frequency photo response, carried out using experimental techniques, circuit analysis and 3D full-wave electromagnetic modelling, is presented. The results of this investigation provide valuable new information for the optimisation of the UTC-PD to antenna coupling efficiency. New THz antenna and antenna array designs, obtained by means of full wave modelling, are also presented, and shown to be suitable for integration with both standard silicon lenses and a novel solution employing a ground plane. The accurate antenna design, along with the results of the UTC-PD impedance investigation, enables the prediction of the power radiated by antenna integrated UTC-PDs, not only in terms of trend over the frequency range but also of absolute level of emitted power. 3D full-wave modelling has also been used at optical frequencies, to address the problem of the optical fibre-to-chip coupling efficiency, which is another fundamental factor for the optimisation of a photonic THz emitter. Among other features, this analysis enables a better understanding of how the light is absorbed throughout the device structure and provides key information for future realisation of travelling-wave photodetectors. An additional experimental tool for the analysis of THz emission, namely the sub-wavelength aperture probe, has been modelled and characterised, revealing interesting properties for the characterisation of antenna far-fields and near fields, and hence providing a valuable tool for THz antenna analysis and design.
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Clegg, James. "Polarisation microscopy of single emitters." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/30775.
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This thesis contains a report on the development of a new type of confocal microscope. The microscope aims to allow the user to be able to determine the three dimensional orientation of single fluorescent emitters. The microscope has at its heart a binary spatial light modulator that allows us to control the excitation electric field in the pupil of the microscope objective. This allows us to exploit the fact that the excitation of, and emission from, a single fluorescent emitter is polarisation and orientation dependent. By changing the field in the excitation pupil we can generate a set of images that when taken together can be analysed to find the emitter orientation. We show that the microscope allows us to resolve the orientation of single fluorescent molecules and nitrogen vacancy centres in nanodiamond. We designed the microscope from scratch using extensive mathematical modelling techniques. We anticipate that these models will be useful to other researchers. One example is that our model of the polarisation distortions introduced during scanning is relevant to any galvanometer-based scanning system. We also developed a full model of a confocal microscope that includes the dipole-like nature of many samples. We use this to calculate, amongst other things, the optical sectioning properties of confocal microscopes. This allows us to validate previous models that ignored polarisation distortions of high numerical aperture lenses and also to make calculations where previous models would have been inadequate, for example in calculating the sectioning strength of sheets of aligned dipoles. As well as developing numerical models, we invented a new method for controlling the polarisation of light using a binary spatial light modulator. This work has applications in materials science, and industrial applications.
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Piechotka, Markus [Verfasser]. "Design and development of miniaturized epoxy-based colloid emitters and solid-state ion-emitters / Markus Piechotka." Gießen : Universitätsbibliothek, 2015. http://d-nb.info/1074437462/34.
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Koehler, Ralf. "Constraining Cosmology with Lyman-alpha Emitters." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-100483.
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Purnell, Sasha Justine. "Fetal dosimetry from natural alpha emitters." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311370.
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Diaz, Gómez Maqueo Pablo (Pablo Ly). "Electrospray emitters For diffusion vacuum pumps." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67181.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 85-87).
Following similar principles as regular diffusion vacuum pumps, an electrospray emitter is set to produce a jet of charged particles that will drag air molecules out of a volume. To be a feasible concept, the emitted particles should have enough momentum to make the colliding air particles being effectively removed from the volume. Also the density of the droplets should be such that the mean free path of air molecules to electrosprayed droplets is in the order of magnitude of the testing setup. A theoretical model is developed for estimating the pumping speed and the importance of the conductivity of the working fluid is identified. Experimental results show an interesting effect. as the pressure difference between two volumes separated by an aperture, is reduced when an electrospray emitter is on. It is showed that a single emitter is expected to have a very low pump capacity, so an array of emitters is proposed as solution. This thesis also comments on the applicability of powder compression molding for the fabrication of emitter arrays. Powder compression molding consists in manufacturing the emitter array out of a plastic - metallic powder feedstock. It consists on 4 steps: (1) Mixing of feedstock, (2) Compression molding, (3) Debinding and (4) Sintering. Initial experiments on compression molding are successful in reproducing arrays of micropillars.
by Pablo Diaz Gomez Maqueo.
S.M.
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Dvorson, Leonard 1974. "Field emitters with integrated focusing electrode." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/80243.
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Gow, Paul C. "Schottky enhanced photo-Dember terahertz emitters." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/410297/.
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The unique properties of terahertz (THz) radiation make it useful for application in the field of imaging. The use of THz time-domain spectroscopy (THz-TDS) systems for the identification and characterisation of various materials is becoming more widespread, with this technology being applied in industry, security and scientific research. The common method for generating THz in commercial TDS systems is through the use of photoconductive antennas (PCA's). These are semiconductor-based devices capable of generating several W of power. PCA's require an external bias to generate a strong electric field across a small electrode gap. However, the high fields generated cause electromigration of the electrode metals and can result in damage to the antenna. This thesis investigates the lateral photo-Dember (LPD) effect; a method of generating THz radiation from a semiconductor without the need for an applied electrical bias. The LPD effect relies on the difference in mobilities between electrons and holes to create opposing dipoles parallel to the semiconductor surface. The selective suppression of dipoles formed underneath a metal mask due to reflection then introduces the asymmetry required for observable THz radiation. In this thesis the generation mechanism behind the LPD effect is investigated using 1D and 2D models, as well as the effect of the presence of a metal mask to suppress dipoles. The output from LPD emitters is enhanced through multiplexing and two different designs are investigated and fully characterised. The novel double-metal multiplexed emitters are then used to demonstrate THz beam shaping and focusing through control of the optical pump beam and a lensless THz-TDS system is proposed.
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McBryde, Duncan. "Multiple lateral photo-Dember terahertz emitters." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/390180/.
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Pulsed terahertz time-domain systems (THz-TDS) offer many applications for spectroscopy and imaging. Typically terahertz generation is achieved by using a photoconductive antenna to generate an electric field (of about 10 kV cm-1) across a semiconductor. By creating such an electric field electro-migration occurs within the photoconductive antenna to eventually bridge the antenna electrodes. As a result photoconductive switches used for terahertz generation have a limited lifetime dependent on the voltage applied to them. This thesis investigates the lateral photo-Dember (LPD) effect as an alternative emitter that does not require an applied electric field. The photo-Dember effect relies on the difference in electron and hole mobility within semiconductors creating a current surge on photo-excitation. The lateral photo-Dember effect works by partially covering regions of the diffusion area to selectively suppresses the terahertz emission radiated by diffusion current. By selecting lateral currents the LPD emitters work in the same configuration as photoconductive antennas while only requiring a metallic boundary near photo-excitation. We investigate the mechanism of the photo-Dember effect and the suppression that causes the LPD effect. Both 1D and 2D models are demonstrated to for calculating diffusion currents within semiconductors and are used within finite element modelling to demonstrate dipole suppression. Optical fluence, beam position and polarisation are characterised within GaAs LPD emitters with SI-GaAs showing a competing generation mechanism from the Schottky barrier at high fluences. We find that the emitter dependence on optical polarisation is due to plasmonic enhancement that occurs on the metal boundary. We demonstrate a simple to fabricate multiplexed LPD emitter based on metals with different reflectivities within the terahertz regime that can be scaled over a large area and propose a design using plasmonic enhancement.
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Ge, Dandan. "Advanced Anisotropic Hybrid Plasmonic Nano-emitters." Thesis, Troyes, 2021. http://www.theses.fr/2021TROY0005.
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Bien que les nanosystèmes plasmoniques hybrides basés sur l'interaction entre les émetteurs quantiques et les nanostructures métalliques aient suscité beaucoup d'attention en raison de la possibilité de développer des nanosources contrôlables, le contrôle de la position relative des nano-émetteurs et des nanostructures métalliques reste difficile. Cette thèse vise à développer des nano-émetteurs plasmoniques hybrides anisotropes via une polymérisation à deux photons en champ proche qui est déclenchée par une amélioration localisée du champ à partir de plasmon de surface supportés par des nanoparticules métalliques. En piégeant les nano-émetteurs (QD) à l'intérieur du polymère ou à sa surface, la distribution du nano-émetteur peut être contrôlée en conséquence en contrôlant la distribution spatiale du polymère au voisinage des nanostructures métalliques. En diminuant le nombre de QD à l'intérieur des lobes de polymère, on obtient un nano-émetteur hybride à base de cube avec un seul QD contenuAlthough the hybrid plasmonic nanosystems based on the interaction between quantum emitters and metallic nanostructures have been receiving much attention because of the possibility for developing controllable nanosources, controlling the relative position of nano-emitters and metal nanostructures remains challenging. This thesis has aimed at developing anisotropic hybrid plasmonic nano-emitters via near-field two-photon polymerization that is triggered by localized field enhancement from surface plasmon supported by metal nanoparticles. By trapping the nano-emitters (QDs) inside the polymer or at its surface, the distribution of the nano-emitter can be controlled accordingly by controlling the spatial distribution of the polymer in the vicinity of the metal nanostructures. By decreasing the number of QDs inside polymer lobes, a hybrid cube-based nano-emitters with only a single QD contained is achieved
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Vemuri, Padma Rekha. "Surface Plasmon Based Nanophotonic Optical Emitters." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc5584/.
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Group- III nitride based semiconductors have emerged as the leading material for short wavelength optoelectronic devices. The InGaN alloy system forms a continuous and direct bandgap semiconductor spanning ultraviolet (UV) to blue/green wavelengths. An ideal and highly efficient light-emitting device can be designed by enhancing the spontaneous emission rate. This thesis deals with the design and fabrication of a visible light-emitting device using GaN/InGaN single quantum well (SQW) system with enhanced spontaneous emission. To increase the emission efficiency, layers of different metals, usually noble metals like silver, gold and aluminum are deposited on GaN/InGaN SQWs using metal evaporator. Surface characterization of metal-coated GaN/InGaN SQW samples was carried out using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Photoluminescence is used as a tool for optical characterization to study the enhancement in the light emitting structures. This thesis also compares characteristics of different metals on GaN/InGaN SQW system thus allowing selection of the most appropriate material for a particular application. It was found out that photons from the light emitter couple more to the surface plasmons if the bandgap of former is close to the surface plasmon resonant energy of particular metal. Absorption of light due to gold reduces the effective mean path of light emitted from the light emitter and hence quenches the quantum well emission peak compared to the uncoated sample.
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Chen, Kevin Chia-lun. "Lead-related quantum emitters in diamond." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/121736.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 39-45).
This thesis reports on quantum emission from Pb-related color centers in diamond following ion implantation and high temperature vacuum annealing. First-principles calculations predict a negatively-charged Pb-vacancy center in a split-vacancy configuration, with a zero-phonon transition around 2.3 eV. Cryogenic photoluminescence measurements performed on emitters in nanofabricated pillars reveal several transitions, including a prominent doublet near 520 nm. The splitting of this doublet, 5.7 THz, exceeds that reported for other group-IV centers. These observations are consistent with the PbV center, which is expected to have the combination of narrow optical transitions and stable spin states, making it a promising system for quantum network nodes.
by Kevin Chia-lun Chen.
S.M.
S.M. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Villapando, Alyanna Zsalee. "Membrane deflection in inline drip emitters." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123244.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (page 25).
This study explores the behavior of membranes found within inline drip emitters when subjected to a concentrated load. Knowing the response of the membrane can be useful in optimizing future emitter designs for characteristics such as lower activation pressure. Two different types of membranes were studied, one from the Jain Turbo Cascade® emitters, and the other from the Jain Turbo Top® emitters. These membranes were placed in a fixture, and a texture analyzer fitted with a ball-end probe was used to measure the force exerted by the membrane at a given deflection. The results were compared to analytical models of the deflection of a simply-supported or clamped rectangular plate with a point load, and it was found that these models do not accurately describe the measured behavior. A sensitivity analysis of the models show that changes in the value of the membrane thickness have the greatest effect on change in theoretical deflection at a given force.
by Alyanna Zsalee Villapando.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Weynand, Vance Leo. "Evaluation of the application uniformity of subsurface drip distribution systems." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/211.
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The goal of this research was to evaluate the application uniformity of subsurface drip distribution systems and the recovery of emitter flow rates. Emission volume in the field, and laboratory measured flow rates were determined for emitters from three locations. Additionally, the effects of lateral orientation with respect to slope on emitter plugging was evaluated. Two different emitters were tested to evaluate slope effects on emitter plugging (type Y and Z). The emitters were alternately spliced together and installed in an up and down orientation on slopes of 0, 1, 2 and 4% and along the contour on slopes of 1 and 2%. The emitters were covered with soil and underwent a simulated year of dosing cycles, and then flushed with a flushing velocity of 0.6 m/s. Initial flow rates for the two emitter types were 2.38 L/hr with a C.V. of 0.07. There was no significant difference in flow rates among slopes for type Y emitters, but there was a significant difference between the 1% and 2 % contour slopes for type Z emitters. Application uniformity of three different laterals at each site was evaluated. Sections of the lateral from the beginning, middle and end were excavated and emission volumes were recorded for each emitter. Application uniformity of laterals ranged from 48.69 to 9.49%, 83.55 to 72.60%, and 44.41 to 0% for sites A, B, and C, respectively. Mean emitter flow rate was 2.21, 2.24, and 2.56 L/hr for sites A, B, and C, respectively under laboratory conditions. Application uniformity under laboratory conditions ranged from 70.97 to 14.91%, 86.67 to 79.99%, and 85.04 to 0.00% for sites A, B, and C, respectively. A flushing velocity of 0.15 m/s with no chlorination, shock chlorination of 3400 mg/L and flushing velocity of 0.15 m/s, and shock chlorination of 3400 mg/L and flushing velocity of 0.6 m/s treatment regiments were applied to all laterals collected to assess emitter flow rate recovery to the nominal flow rate published by the manufacturer. All laterals showed an increase in the number of emitters within 10% of the published nominal flow rate.
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Hernández, García David. "Selective thermal emitters based on photonic crystals." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/284201.
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Un dels límits fonamentals que afecta l'eficiència de conversió en cèl·lules fotovoltaiques és la distribució espectral de la radiació solar. D'una banda, només els fotons amb energia superior al gap del semiconductor poden convertir-se en electricitat a la cèl·lula. Els fotons de baixa energia no generen parells electró-forat. D'altra banda, l'excés d'energia dels portadors generats per fotons de molt alta energia es perd ràpidament per termalització en el propi dispositiu. Aquests fotons d'alta energia no generen una major energia elèctrica, pel que l'excés d'energia òptica es perd. Per superar aquesta limitació, la investigació s'ha centrat majoritàriament en millorar la conversió directa de fotons d'alta i baixa energia a través de, per exemple, l'ús d'up- i down-converters. Una alternativa menys estudiada consisteix en adaptar la radiació solar al dispositiu com a pas previ a la conversió. Aquesta adaptació es realitza mitjançant l'ús d'emissors selectius òpticament adaptats al semiconductor. Un emissor selectiu és un material amb una emissió tèrmica que ocupa una banda espectral estreta, en comptes d'emetre en tot l'espectre freqüencial. Aquests emissors són una alternativa eficient per obtenir grans conversions, treballant a temperatures al voltant dels 1500 K, donat que un material calentat pel Sol, o una altra font d'energia, pot reemetre llum amb una distribució espectral molt més adequada al dispositiu fotovoltaic. Aquest mode d'operació es coneix com a conversió d'energia termofotovoltaica. A la natura existeixen materials capaços de comportar-se com emissors selectius. Els òxids de terres rares representen un interesant camp d'investigació. Aquests òxids tenen una emissió tèrmica molt baixa en tot l'espectre excepte a certes freqüències. Aquestes freqüències d'emissió són úniques i selectives i provenen de ressonàncies a l'estructura cristal·lina del material. El desavantatge en la seva utilització radica en què la posició espectral d'aquests pico d'emissió, propis del material i la seva estructura, no pot ser controlada. A més, aquestes bandes d'emissió són relativament estretes, generant una baixa densitat de potència radiada. Per tant, existeix la necessitat de treballar amb materials amb una banda d'emissió selectiva que pugui ser dissenyada i controlada convenientment. La solució és l'ús de cristalls fotònics (materials artificials amb propietats òptiques que no existeixen en la natura). Encara que la seva fabricació presenta molts reptes, aquests cristalls artificials permeten el control de l'emissió espontània, suprimint-la o potenciant-la a la banda freqüencial d'interès. Existeixen varies interaccions que permeten aquest control: l'efecte de banda prohibida, la interacció per plasmons o fonons, o l'efecte de microcavitat. Tots permeten modificar l'espectre d'emissió tèrmica d'un material. La present tesis doctoral està dedicada a l'estudi de les propietats d'emissió tèrmica, i estabilitat tèrmica, d'emissors selectius basats en cristalls fotònics. S'han analitzat varies estructures: cristalls fotònics basats en silici macroporós, quasi-cristalls fotònics i microcavitats metàl·liques. També, en col·laboració amb altres grups d'investigació, s'han analitzat les propietats tèrmiques de cristalls col·loïdals. En el present treball, es mostra que els cristalls i quasi-cristalls basats en silici macroporós poden inhibir eficientment la radiació tèrmica de manera controlable, sent a més estables a alta temperatura fins 1500 K. Respecte els cristalls metàl·lics, l'estudi realitzat mostra la seva alta selectivitat espectral, encara que aquests emissors han de treballar a temperatures inferiors a 1100 K per garantir la seva estabilitat estructural i òptica.One of the fundamental limits of conversion efficiency in photovoltaic cells is the broadband distribution of solar spectrum. On one hand, only photons with energy higher than the semiconductor's bandgap can be converted in the device, on the other hand, carriers generated by high energy photons rapidly loose their excess of energy by thermalization with the lattice. To overcome this limitation, and span the useful convertible region of solar spectrum, many approaches have focused on improving the direct photon to electron conversion by the development of up- and down-converters. A less studied alternative, however, is the use of spectrally narrow distributed emitters, optically matched with the gap energy of the photovoltaic cell, instead of direct sunlight. Indeed, a material heated by the sun, or another energy source as methane or hydrogen, can re-emit light with suitable spectral distribution and significant higher power density, improving conversion efficiencies in solar cells. This way of operation is known as thermophotovoltaic energy conversion. Several materials have been considered to be used as emitters in thermophotovoltaic systems. Silicon carbide is a common one, thanks to its high stability at temperatures up to >2000 K. However, its broadband spectral emission limits the conversion efficiency in the photovoltaic device and forces to work at elevated temperatures. Selective emitters, which stand for materials whose thermal emission occupies a narrow spectral region, are a promising alternative to reach elevated conversion efficiencies at lower temperatures. Natural selective emitters as rare earths have attracted considerable research interest as they present unique emission peaks with the highest emittance level. This approach, however, presents some drawbacks, the spectral position where strong emission appears is not controllable, and the width of the emission band is relatively narrow, leading to a low power density emitted by the source. An advantageous way to engineer the selective emission of a thermal source and control the spectral position and bandwidth of strong emission, is by making use of photonic crystals (articial materials engineered to show optical properties that may not be found in nature). The spectral control of the spontaneous emission in such materials is a unique feature of photonic crystals, although their fabrication, mainly in three-dimensions, is still challenging. Several interactions between photonic crystals and radiation have been reported: the photonic bandgap effect, surface plasmon polaritons, phonon polaritons, or the microcavity effect, to give some examples. All these approaches allow engineering the thermal emission of materials to match the energy band of the photovoltaic cell and benefit the optical to electrical conversion efficiency, although some limitations arise when utilized in high temperature thermophotovoltaic systems which will be analyzed during the realization of this thesis. This thesis is therefore devoted to the study of the thermal emission properties and thermal stability of photonic crystal based selective emitters. Various structures have been analyzed: macroporous silicon crystals, photonic quasi-crystals and metallic microcavities. A study in self-assembled colloidal crystals was also started and the preliminary results are presented in the appendix of the document. Here, it is demonstrated that macroporous silicon crystals and quasi-crystals can inhibit thermal radiation in a controllable manner with thermal stability up to 1500 K. The great selective emission properties of metallic microcavities is also demonstrated, although the working temperature of such structures is limited below 1100 K to prevent degradation of the metallic layer.
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Langner, Maik. "Laterally modified microcavity systems containing organic emitters." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-67568.
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The scope of this work is an in-depth investigation of dielectric mirror microcavities with central organic dye layers, which are preferably modified in at least one lateral dimension. The large quality factor of the planar resonator in conjunction with comparatively stable and spectrally broad emitting molecules allows for a detailed analysis of several aspects of microresonator systems. Their optical properties are analyzed both with transmission and luminescence measurements as well as in the lasing regime.
The first part presents the resonant mode properties of planar and laterally structured microcavities. With the help of a high-resolution imaging micro-photoluminescence setup, working either in the spatial (near field) or vectorial (far field) regime, the polarization splitting is studied in a detuned microcavity, containing the dye 4,4'-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) in a matrix of 4,4'-di(N-carbazolyl)- biphenyl (CBP). With the help of a thickness gradient, a relation between the large spectral distance of the cross-polarized states and the mode position within the stop band is investigated. In shadow-mask prepared, laterally restricted devices (5x5 µm2 square boxes), the three-dimensional confinement introduces sets of discrete modes, which experience a similar polarization splitting. The origin in this case is a different phase shift of electromagnetic waves during internal total reflection at a boundary.
By using a concentration gradient planar microcavity sample of the dye 4-(dicyanomethylene)-2-methyl-6-(4-(dimethylamino)styryl)-4H-pyran (DCM) in a tris-(8-hydroxyquinoline)aluminum (Alq3) matrix, the influence of the number of emitters on the lasing characteristics is subsequently analyzed. Depending on the pumping conditions, and thus the involvement of the Förster resonant energy transfer, an optimal composition is identified. After a qualitative evaluation of the long-term stability upon various excitation energies, the attention is focussed to the modification of the stimulated emission properties of photonic boxes. The stronger field concentration and altered density of states leads to a significant improvement of the values for the coupling factor fi and the threshold levels. Furthermore, new properties arise, namely simultaneous multimode and off-axis laser emission. With an inhomogeneous excitation of the box, it is possible to selectively excite single modes above the threshold.
The work ends with experimental results of metal structures as additional optical element in the organic microcavity layer. Here, the aim is is to understand the passive influence of these possible contact- devices on the lasing performance. For this purpose, the lasing is studied at an interface of an areal thin metal layer, which is incorporated in the organic layer.
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Stevens, Renaud. "Modulation Properties of Vertical Cavity Light Emitters." Doctoral thesis, Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3240.
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Diehl, Laurent. "Development of Si/SiGe quantum cascade emitters." Online version, 2004. http://bibpurl.oclc.org/web/24144.
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Wölfl, Friedrich. "Intensity noise studies of semiconductor light emitters." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342990.
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Daniels, Ruth. "Multimetallic emitters for bioimaging and display applications." Thesis, Northumbria University, 2017. http://nrl.northumbria.ac.uk/36272/.
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The luminescent properties of transition metal complexes of heavy metals such as platinum(II) and irdium(III) are often highly luminescent and therefore are interesting for use as phosphorescent dopants in organic light-emitting diodes (OLEDs) and as luminescent probes in bioimaging. The majority of complexes investigated to date contain only one metal centre with multimetallic complexes becoming more widely studied in recent decades. This work explores the synthesis of novel dinuclear emitters based on cyclometallated Pt(II) and Ir(III) centres. In particular, complexes in which the metal centres are rigidly-linked via cyclometallating bridging ligands. The complexes described in this work are highly luminescent with high quantum yields in degassed solution and relatively short luminescence lifetimes. Dinuclear platinum(II) complexes linked via pyrimidine-based bis-bidentate ligands incorporating mono- and bis-thiophene cyclometallating units have been prepared and their photophysical properties investigated. These complexes were observed to emit in the orange (610 nm) and near-infrared (730 nm) regions of the spectrum for the mono- and bis-thiophene respectively, with relatively high quantum yields (φ = 0.15–0.85). A further dinuclear platinum(II) complex, rigidly-linked via a bis-tetradentate bridging ligand offering O^N^C^N coordination, was successfully prepared. To the best of our knowledge, this is the first example of di-platinum(II) complex in which the two metal centres are linked via this type of bridging ligand. Dinuclear iridium(III) complexes linked via bis-bidentate bridging ligands based on the central heterocycle pyrimidine have been prepared. These pyrimidine-linked complexes exhibited high quantum yields in degassed dichloromethane solution at room temperature, in the range 0.88-1.0. A representative structure is shown below. Variation of the monodentate chloride ligands to alternative ligands such as cyanide and acetonitrile was also investigated. Incorporation of a cyanide ligand was observed to blue-shift the emission relative to the analogous chloro complex. The effect of varying the central heterocycle of the bis-bidentate bridging ligand was investigated. The identity of the central heterocycle of the bridging ligand has been shown to have significant effects on the properties of the resulting dinuclear Ir(III) complexes, as is discussed below. Di-iridium(III) complexes linked via 2,5-pyrazine based bridging ligands have been successfully prepared. However, photodegradation of the complexes was observed in chlorinated solvents. To resolve this problem, a bis-bidentate bridging ligand incorporating a thiazolo[5,4]thiazole core was employed and the resulting di-iridium complex showed improved photostability. A 2,3-pyrazine-linked dinuclear iridium complex was synthesised and was observed to have a twisted geometry at room temperature and therefore, is chiral. Through a high-temperature NMR experiment, it was shown that this complex racemises at 80 °C. Finally, incorporating pyridazine as the central heterocycle leads to the sharing of a monodentate chloride ligand between the two iridium centres. This leads to the formation of a cationic dinuclear iridium(III) complex. This complex was investigated as a luminescent probe in bioimaging.
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Hillebrand, Anne. "Coloured graph models : associating emitters and ships." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:54e2170e-ec6b-4bdc-886f-d9bc1468fce8.
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This thesis examines graph-theoretic approaches to problems arising in emitter- to-platform association, for example in associating emitters and ships. The first part of this thesis focuses on emitters that are observed by two different sensors, which can only determine the bearing the observed signal was emitted from. The aim is to pair observations from the two sensors, that originate from the same emitter. In this thesis it is shown that different types of observations can be represented as one of c colours and each observed bearing as a row or a column in an n by n grid. Given the horizontal and vertical projections of a coloured grid, the aim is to reconstruct the original layout of the coloured squares on the grid. Deciding whether two sets of positive natural numbers are the horizontal and vertical projections of a coloured grid is NP-complete for two or more colours [24, 35, 47] and has close connections to colour degree matrix problems. Necessary and sufficient conditions are known for a demand matrix to be a colour degree matrix of an edge-coloured forest [9, 22]. In this thesis the first step beyond forests is taken: necessary and sufficient conditions for a demand matrix to be realisable by a graph with at most one cycle are proved. As part of the proof some directly forced structures are discovered, that is, structures that must exist in every realisation. Moreover, corresponding results for multi-graphs and pseudoforests with at most k cyclic components are presented. This part concludes with O (n2 ) time algorithms to check these conditions and return a witness if one of the conditions is violated. Finally O(n3) time algorithms to find a realisation, if one exists, are described. The second part of this thesis introduces the coloured L-model. This is an original idealised graph model, developed to explore the combinatorial properties of the emitter-to-platform association problem, referred to as the reverse radar problem in this thesis. The aim is to decide which groups of observed radars originate from the same ship, taking into account which combinations of radar models are known to be carried by different types of ships. It is shown what exactly makes finding a solution to this idealised version of the reverse radar problem NP-hard, and that there are tractable cases equivalent to finding (weighted) matchings in related graphs, which have bounded pathwidth. Restricting to graphs with bounded pathwidth is a reasonable simplification, as signals come in along bearings (i.e. along a cycle) and a cycle has pathwidth two. New algorithms to find (weighted) matchings in graphs with bounded pathwidth and treewidth are presented, which can be used to solve the reverse radar problem in this model. Finally, the likelihood and two-time models are introduced, which complement the coloured L-model by generalising measurement errors and by introducing time. It is shown that the problem remains NP-hard, even for very simple cases and some tractable cases are described.
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SAMIEE, MAHMOOD. "COLD ELECTRON EMITTERS BASED ON POLYCRYSTALLINE DIAMOND." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1116185810.
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Kobayashi, Masakazu. "Lyman alpha emitters in hierarchical galaxy formation." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136886.
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Samiee, Mahmood. "Cold electron emitters based on poly crystalline diamond." Cincinnati, Ohio : University of Cincinnati, 2005. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1116185810.
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Smith, Richard Charles. "Electron field emission properties of tip based emitters." Thesis, University of Surrey, 2005. http://epubs.surrey.ac.uk/843091/.
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Large area displays such as laptop computers and flat screen televisions have enormous market potential. There are numerous technologies in existence today, including LCD (liquid crystal displays) and plasma, however they each suffer from unique limitations, mainly the size of the display and operating conditions. There is still a need for a method of depositing electronic materials over large areas at suitable temperatures. This is important since the construction of panels using sub-modules such as crystalline silicon wafers is very difficult and expensive. The displays based on liquid crystals that use thin film transistor (TFT) driven active matrix addressing is the most common flat screen technology at present. However, there are great problems associated with yield in fabrication, especially for screen dimensions over 14 inches. Hence the screens are very expensive. Field emission displays utilising the phenomenon of field emission in which electrons escape their work function and "jump" from the surface of the semiconductor into a vacuum has been proposed as a competing technology. Each pixel is controlled by many tip based emitters, therefore improving the yield. This thesis explores the field emission properties and mechanisms of tip based emitters, and also explore the possibility of utilising carbon nanotubes as electron sources for field emission displays.
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Tomczak, Nikodem. "Single light emitters in the confinement of polymers." Enschede : University of Twente [Host], 2005. http://doc.utwente.nl/57484.
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Thijssen, Arthur Christianus Theodorus. "Polarisation engineering of nanophotonic structures containing quantum emitters." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601176.
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In this thesis I will investigate photonic structures that can be utilised to entangle the electron spin of a self-assembled quantum dot with a photon. Charged. quantum dots, whose emitted photons are trapped or guided by the photonic structure, can be utilised as quantum memories and form the basic building block of the interface. It will be shown, using a dyadic Green's function method, that photonic structures need to fulfil! two criteria in order to implement a spin-to-photon interface. Criterion one is the support of a degenerate mode, criterion two requires the quantum dot to couple equally to the two orthogonal modes. Only a subset of photonic structures fulfill these requirements. Two structures that fulfill these criteria are investigated in more detail using the dyadic Green's function method developed, and I show that both structures enable in-plane spin readout, which had not been demonstrated yet. The first, a cross configuration of two nanowire waveguides, couples a spin state to different waveguides of the cross configuration. By recombining two of the four arms and interfering the outputs spin readout is made possible. It will be shown that the device has two working regimes for spin readout depending on the quantum dot position. The structure works well in both regimes. The second structure, a photonic crystal waveguide, enables in-plane spin readout by positioning the quantum dot on a circular polarisation singularity resulting in directional coupling of different spin states. Subsequently, I will show that this structure is able to generate spin-photon and photon-photon entanglement by reflecting photons of the waveguide.
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Fu, Wai-yuen, and 傅惠源. "A comprehensive approach to high efficiency light emitters." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841537.
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The Best MPhil Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2008-2009published_or_final_version
Electrical and Electronic Engineering
Master
Master of Philosophy
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Liu, Yuh-Shiuan. "Ultraviolet emitters grown by metalorganic chemical vapor deposition." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50415.
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This thesis presents the development of III-nitride materials for deep-ultraviolet (DUV) light emitting devices. The goal of this research is to develop a DUV laser diode (LD) operating at room temperature. Epitaxial structures for these devices are grown by metalorganic chemical vapor deposition (MOCVD) and several material analysis techniques were employed to characterize these structures such as atomic force microscopy, electroluminescence, Hall-effect measurement, photoluminescence, secondary ion mass spectrometry, transmission electron microscopy, transmission line measurement, and X-ray diffraction. Each of these will be discussed in detail. The active regions of III-nitride based UV emitters are composed of AlxGa1-xN alloys, the bandgap of which can be tuned from 3.4 eV to 6.2 eV, which allows us to attain the desired wavelength in the DUV by engineering the molar fraction of aluminum and gallium. In order to emit photons in the DUV wavelength range (> 4.1 eV), high aluminum molar fraction AlxGa1-xN alloys are required. Since aluminum has very low ad-atom mobility on the growth surface, a very low group V to group III precursor ratio (known as V/III ratio), high growth temperature, and low growth pressure is required to form a smooth surface and subsequently abrupt heterointerfaces. The first part of this work focuses on developing high-quality multi-quantum well structures using high aluminum molar fraction ([Al] > 60%) AlxGa1-xN alloys. Optically pumped DUV lasers were demonstrated with threshold power density as low as 250 kW/cm² for the emission wavelength as short as 248.3 nm. Transverse electric (TE) -like emission dominates when the lasers were operating above threshold power density, which suggests the diode design requires the active region to be fully strained to promote better confinement of the optical mode in transverse direction. The second phase of this project is to achieve an electrically driven injection diode laser. Owing to their large bandgap, low intrinsic carrier concentration, and relatively high dopant activation energy, the nature of these high aluminum molar fraction materials are highly insulating; therefore, efficiently transport carriers into active region is one of the main challenges. Highly conducting p-type material is especially difficult to achieve because the activation energy for magnesium, a typical dopant, is relatively large and some of the acceptors are compensated by the hydrogen during the growth. Furthermore, due to the lack of a large work function material to form a p-type ohmic contact, the p-contact layer design is limited to low aluminum molar fraction material or gallium nitride. Besides the fabrication challenges, these low aluminum molar fraction materials are not transparent to the laser wavelength causing relatively high internal loss (αi). In this work, an inverse tapered p-waveguide design is employed to transport holes to active region efficiently while the graded-index separate-confinement heterostructure (GRINSCH) is employed for the active region design. Together, a multi-quantum well (MQW) ultraviolet emitter was demonstrated.
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Cuthbertson, A. "Self-aligned bipolar transistors with polysilicon contacted emitters." Thesis, University of Southampton, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356059.
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Girgel, Ionut. "Development of InGaN/GaN core-shell light emitters." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720648.
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Gallium nitride (GaN) and its related semiconductor alloys are attracting tremendous interest for their wide range of applications in blue and green LEDs, diode lasers, high-temperature and high-power electronics. Nanomaterials such as InGaN/GaN core-shell three-dimensional nanostructures are seen as a breakthrough technology for future solid-state lighting and nano-electronics devices. In a core-shell LED, the active semiconductor layers grown around a GaN core enable control over a wide range of wavelengths and applications. In this thesis the capability for the heteroepitaxial growth of a proof-of-principle core-shell LED is advanced. A design that can be applied at the wafer scale using metalorganic vapor phase epitaxy (MOVPE) crystal growth on highly uniform GaN nanorod (NR) structures is proposed. This project demonstrates understanding over the growth constraints of active layers and dopant layers. The impact of reactor pressure and temperature on the morphology and on the incorporated InN mole fraction was studied for thick InGaN shells on the different GaN crystal facets. Mg doping and effectiveness of the p-n junction for a core-shell structure was studied by extensive growth experiments and characterization. Sapphire and Si substrates were used, and at all the stages of growth and fabrication. The structures were optimized to achieve geometry homogeneity, high-aspect-ratio, incorporation homogeneity for InN and Mg dopant. The three-dimensional nature of NRs and their light emission provided ample challenges which required adaptation of characterization and fabrication techniques for a core-shell device. Finally, an electrically contacted core-shell LED is demonstrated and characterized. Achieving a proof-of-principle core-shell device could be the starting point in the development of nanostructure-based devices and new physics, or in solving technical problems in planar LEDs, such as the polarization of emitted light, the quantum-confined Stark effect, efficiency droop, or the green gap.
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Kelsall, Colin Clancy. "Cavity absorber-emitters for high-temperature solar thermophotovoltaics." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120194.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 63-64).
Solar energy has been an important component of the world's energy infrastructure for many years, but certain limitations have hindered its ability to become a primary source of renewable energy. In particular, intermittency and fundamental limitations on conversion efficiency have restricted adoption of direct photovoltaic conversion with PV cells. Recent developments in more advanced cell chemistries and concentrated solar power systems (CSP) seek to address some of these limitations and enable higher grid penetration of solar derived power. This thesis examines one of these such technologies, solar thermophotovoltaics (STPV), and presents opportunities to improve on past work in the field to enable higher conversion efficiencies and lower cost solar power. STPV power systems typically utilize a monolithic absorber-emitter component that is heated with concentrated sunlight through a highly absorptive surface. The monolith radiatively illuminates a low-bandgap PV cell from a different, spectrally selective emitter surface, producing electricity. This added spectral selectivity allows for improved photovoltaic conversion efficiencies compared to a standard PV cell illuminated with the solar spectrum. STPV systems, however, often operate above 1000°C and are hindered by substantial parasitic thermal losses. In this thesis we first present an overview of the loss mechanisms currently limiting STPV system efficiencies and some theoretical approaches to address these losses. Previously demonstrated STPV systems have significant drops in efficiency through re-emission losses from the hot absorber surface. Selective absorber coatings can reduce these losses; however, experimentally demonstrated efficiency improvements have been limited due to non-ideal spectral selectivity and high-temperature instability. Through an alternative approach, we present a purely geometric solution to mitigate re-emission losses by varying the area ratio, defined as the ratio of thermal emitter area to solar absorber area. We model how our solution could theoretically improve previously demonstrated STPV systems and also discuss the practical limitations of our approach. Secondly, we investigate the potential of integrating a cavity-based geometry for the absorber-emitter monolith in place of typical planar designs. By incorporating a cavity in place of the planar absorber-emitter, we take advantage of both increased absorption across the full solar spectrum and enable very high area ratios in a compact design. Third, we address how thermal gradients might develop within the absorber-emitter monolith and how these gradients might impact system performance. We present a numerical model capable of predicting PV cell performance degradation under uneven illumination resulting from emitter temperature gradients. Finally, we validate our model through experiments using cavities made from high-temperature refractory materials and a high-powered laser to emulate highly concentrated sunlight. By integrating a cavity-type absorber-emitter with state-of-the-art spectrally selective surfaces and filters, the maximum system efficiency demonstrated in previous works could be increased from 6.8% to upwards of 9% without any improvements in spectral selectivity. This cavity-type approach, which has the potential to improve solar absorber performance both for STPV and other solar thermal technologies, could help realize the full potential of these systems as efficient and useful methods of solar energy conversion.
by Colin Clancy Kelsall.
S.M.
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Lyth, Stephen Matthew. "Multiwall carbon nanotube inks as electron field emitters." Thesis, University of Surrey, 2007. http://epubs.surrey.ac.uk/844470/.
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The work presented in this thesis is concerned with pure, water-soluble multiwall carbon nanotube inks, in particular their use in the fabrication of inexpensive field emission (FE) cathodes. This work is divided into three parts. Firstly, with the aim of fabricating a transparent FE cathode, nanotube inks are spin-coated onto transparent substrates, which subsequently are subject to laser treatment. An improvement in the FE properties with increasing laser fluency is observed, resulting in threshold fields of less than 6 V/mum (glass substrates) and less than 0.5 V/mum (plastic substrates). Secondly, with the aim of tailoring the geometric enhancement factor to improve the FE properties, nanotube inks are deposited onto paper substrates of varying surface morphology, via dip-coating. The FE properties are found to dramatically improve with increasing surface roughness of the paper, and a threshold field of less than 1 V/mum is achieved. Additionally, laser treatment is used to improve the threshold field. A 3-terminal device is fabricated with nanotube ink on paper substrates, operating with a gate voltage of 60 V and an anode voltage of 400 V. Finally, the effect that the work function has upon the FE properties of nanotube ink is investigated. An improvement in the threshold field from 0.42 to 0.25 V/mum is observed after lithium functionalisation was used to reduce the work function from 5.1 eV to 4.5 eV. Additionally, staircase-like current-field characteristics are observed for carboxylic-functionalised carbon fibres and these effects are discussed in terms of resonant tunnelling.
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Woodhead, Christopher Stephen. "Enhancing the light output of solid state emitters." Thesis, Lancaster University, 2017. http://eprints.lancs.ac.uk/88416/.
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The work in this thesis focuses on improving the light output of room temperature emitting materials, and nanostructures as a stepping stone for use as single photon sources. The primary nanostructures studied are III-V based type-II emitting quantum dots/quantum rings (QDs/QR’s), which emit at telecom wavelengths either in the O-band (GaSb/GaAs QRs) or the C-band (InAs/GaAs QDs capped with GaAsSb). Individual exciton emission at low temperature was observed in these samples using micro-photoluminescence for what we believe is the first time. This was achieved by reducing the excitation area of the sample using micropillars and gold aperture masks, combined with increasing the extraction efficiency of light using a solid immersion lens. The observation of individual exciton emission enabled their contribution to the power dependent blueshift of type-II quantum dots to be studied. The integration of the InAs/GaAs QDs with silicon was explored by studying their emission when they are grown on both GaAs and silicon substrates. Studies such as this are an important step towards integrating QDs with on-chip communications. Finally, solid immersion lenses formed from a UV-curable epoxy are explored as a method for increasing light out of 2D materials. It was found that for Tungsten Diselenide (WSe2) the solid immersion lens increased the intensity of the emitted photoluminescence, as well as preventing the monolayer from degrading. This method could prove to be an excellent method for increasing the light output of 2D material based LED’s, especially WSe2 based single photon sources.
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Chen, Li. "SILICON CARBIDE PRESSURE SENSORS AND INFRA-RED EMITTERS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1195161915.
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O'Regan, Bryan J. "Resonantly enhanced thermal emitters based on nanophotonic structures." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7801.
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The manipulation of photons, especially the control of spontaneous emission, has become a core area of photonics research in the 21st century. One of the key challenges is the control of the broadband emission profile of thermal emitters. Recently, attention has focused on resonant nanophotonic structures to control the thermal emission with most of the work concentrating on the mid-infrared wavelength range and/or based on metallic nanostructures. However, the realisation of a high temperature, single wavelength, narrowband and efficient thermal source, remains a challenge. In this project, four individual nanophotonic resonant structures are presented for the control of thermal emission, all operating in the near-infrared (≈ 1.5 μm) wavelength range. The work is split over two different emission materials; gold and doped silicon. While I present two successful designs of narrowband thermal emitters from gold, the main backbone of the research is concentrated on doped silicon as the emission material. By combining the weak broadband absorption of doped silicon with a photonic crystal resonator, resonantly enhanced narrowband absorption is achieved. Using Kirchhoff's law of thermal radiation which equates the absorptivity and emissivity, narrowband absorption leads to narrowband emission, which is the underlying principle used throughout the work presented in this thesis to achieve narrowband thermal emission. One common oversight in many of the presented thermal emitter designs is the angular emission dependence, i.e. how the emission wavelength behaves away from surface normal. Typically, since the majority of the devices are based on periodic structures, the resonant emission wavelength changes with emission angle, which is not ideal. Here, the angular sensitivity is considered and addressed, by constructing a device that is based on localised confined resonances and not on propagating resonances, it is possible to achieve a truly monochromatic source i.e. one with the same emission wavelength in all directions, all the way up to an angle of 90°. Finally, the devices presented here demonstrate that weak absorption together with photonic resonances can be used as a wavelength-selection mechanism for thermal emitters, both for the enhancement and the suppression of emission away from the resonant wavelength.
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Fu, Wai-yuen. "A comprehensive approach to high efficiency light emitters." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42841537.
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Searle, Andrew. "Application of nanostructured emitters for high efficiency lighting." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:81731b64-c40b-4c76-9c90-dae7c956e29f.
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This is the first study comparing morphologies of CNT films on Kanthal wire, with their field emission properties, and as such offers ways to design better cylindrical emitter devices. A low turn-on field was achieved (0.35 V/µm), the field emission results have been explained using a simple model, and a fluorescent lamp was fabricated. Whilst previous work has been done on the link between “as grown” CNT films and their respective field emission properties on flat substrates, very little work has been done on linking morphology to emission performance on wire substrates, where the morphology can be very different. Microscopic structures such as towers, ridges and clumps consisting of many aligned or entangled CNTs were grown using an aerosol chemical vapour deposition (a-CVD) technique. Hydrogen added to the carrier gas resulted in a decrease in defect density in the growth of undoped CNTs, and an increase in defect density in the growth of nitrogen doped CNTs (N-CNTs) and boron doped CNTs (BCNTs). In-situ transmission electron microscopy (TEM) studies show that damage to CNT tips results in a significantly higher turn-on field compared to undamaged tips. This can be recovered by making the CNT emit current for several minutes which makes the tip recrystallize due to heat caused by the Nottingham effect. The field emission properties of the “as grown” CNT films are dominated by protruding CNTs found at the edges of ridge and tower microscopic structures. The field emission properties are also related to the dimensions of these structures with the longest ridges (hence those with the longest protruding CNTs) resulting in the lowest turn-on electric field. The ridge and tower structures act to accommodate protruding CNTs at their edges and their physical dimensions (mainly width) act to separate these emitters so that screening is minimised. This work shows that efficient emitters can be fabricated effectively from simple a-CVD techniques and microscopic structures act to improve, not degrade, field emission properties.
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Grandi, Samuele. "Single quantum emitters : resonance fluorescence and emission enhancement." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/48463.
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Single photons are highly desirable for encoding, sending and processing quantum information. Suitable engineering of single quantum emitters and their environment can lead to a reliable single photon source and to mediated photon-photon interactions, essential assets for quantum communication and computation purposes. Dye molecules, our chosen single quantum emitter, have attracted much attention in recent years due to their high photostability and narrow emission lines. In this thesis I present a detailed analysis of the optical properties of single dibenzoterrylene molecules in an anthracene matrix. Single photon emission is demonstrated at room and cryogenic temperatures. In the latter case, an analysis of the second-order correlation function of the emission of a single molecule is studied at various temperatures. The data agree with a full solution of the optical Bloch equations over a wide range of temperature, and provide some insight into the dephasing process of the molecules. I then present a technique for integrating single dye molecules with nano-photonic devices. These are hybrid plasmonic waveguides, designed to guide light and to enhance the interaction with a single emitter by a tight confinement of the waveguide mode. Single molecules are deposited over the waveguides and a first evidence of coupling is presented. I conclude with proposed improvements to the optical setup and to the deposition methods. Finally, I present another type of integrated device, where the light matter interaction is enhanced by inserting single quantum emitters into coupled optical resonators. The theoretical description for the case of resonant two-photon absorption from single atoms in coupled photonic crystal cavities is developed. I conclude by proposing a possible realisation of this system, and describing the first steps towards the fabrication of such a device.
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Elarabi, Asem S. Amar. "Polarization behavior of high-Tc superconducting terahertz emitters." Kyoto University, 2018. http://hdl.handle.net/2433/235090.
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Aljarrah, Mohannad T. "Modeling and Experimental Validation of Radiative Heat Transfer in Porous Nanocomposites as Selective Emitters for Low Temperature Thermophotovoltaic Systems." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1259561401.
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Peter, F. "Advanced emitters and detectors for terahertz time-domain spectroscopy." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-61479.
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The idea of terahertz-time-domain spectroscopy (THz-TDS) is to exploit a single cycle, spectrally broad THz radiation pulse to gain insight into the response of matter. Photoconductive devices and nonlinear crystals are utilized in both the generation as well as the coherent detection of THz radiation. The relatively high cost and the complexity of commonly used titanium-sapphire lasers hinder a more widespread use of pulsed THz systems for commercial applications. Er-doped femtosecond fiber lasers operating at 1.55 μm could offer a viable alternative. In this thesis nonlinear crystals and photoconductive emitters are discussed for excitation in the near infrared (NIR) window of between 800 nm to 1550 nm. The main focus of this thesis is a detailed study of substrate materials for an interdigitated photoconductive antenna. Photoconductive antennas with microstructured electrodes provide high electric acceleration fields at moderate voltages because of small electrode separations. The scalability of these devices allows for large active areas in the mm^2 range, which are sufficient for excitation at large optical powers. In comparison with conventional emitter structures, these antennas have more favourable characteristics regarding THz power, spectral properties, and ease of handling. Depending on the utilized substrate material, photoconductive antennas can then be operated using different excitation wavelengths. By employing substrates with short carrier trapping times these antennas can be operated as THz-detectors. Moreover the design of electrode structures for generating radially and azimuthally polarized THz waves are presented. A second topic deals with the signal analysis and signal interpretation of THz pulses transmitted through several material systems. These experiments show the potential for tomographic and spectroscopic applications. The third part deals with THz emission by frequency mixing in nonlinear organic and inorganic crystals. Hereby the focus is on polaritonic phase matching in GaAs. Furthermore, indications of THz tunability by the excitation wavelength were found by utilizing waveguide structures. However, the observed tuning range is much lower then theoretically predicted. Specific reasons for this are discussed.