Dissertations / Theses on the topic 'Optical physical characterisation'
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Nish, Adrian. "Studies on optical characterisation of carbon nanotube suspensions." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:1ecd4f04-0178-4d8b-bf3a-cd6f8d744b92.
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This thesis reports studies done on single-walled carbon nanotubes (SWNTs) using optical spectroscopy as the primary investigative technique. It focuses on advances in sample preparation which have been made possible through improvements to the method of photo-luminescence excitation (PLE) mapping of nanotubes. An introduction to the field and some theoretical models are presented initially to provide a background to the experimental chapters which follow. A description of the standard procedure for sample preparation in aqueous surfactants is then followed by a detailed introduction to PLE mapping, including modeling of SWNT spectra. The next chapter discusses improvements to the sample preparation method by using organic polymer solutions instead of aqueous surfactants for suspending the nanotubes. The results show reductions in the distribution of SWNT species which are solubilised, leading to significant improvements in the resolution of the optical absorbance spectra and an increased photoluminescence yield. Two experiments which were performed on the novel polymer-SWNT systems are then described. The first shows (via PLE mapping) that energy is transfered to the SWNTs when the polymer is photo-excited. The possible mechanisms behind this, as well as the implications for using carbon nanotubes as an additive in polymer photovoltaics, are discussed. The second experiment details a recent magneto-PL study of SWNTs embedded in films produced from the polymer solutions. Here, the improved optical signatures and absence of strain at low temperatures have revealed a previously unseen high field intensity dependence. The behavior has been explained by the magnetic field induced mixing of the excitonic states.
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McBride, Gillian M. "Physical and optical characterisation of carbon-silicon layers produced by rapid thermal chemical vapour deposition." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286865.
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Kloser, Rudolf J. "Seabed biotope characterisation based on acoustic sensing." Thesis, Curtin University, 2007. http://hdl.handle.net/20.500.11937/524.
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The background to this thesis is Australia’s Oceans Policy, which aims to develop an integrated and ecosystem-based approach to planning and management. An important part of this approach is the identification of natural regions in regional marine planning, for example by establishing marine protected areas for biodiversity conservation. These natural regions will need to be identified on a range of scales for different planning and management actions. The scale of the investigation reported in this thesis is applicable to spatial management at 1 km to 10 km scale and monitoring impacts at the 10s of m to 1 km biotope scale. Seabed biotopes represent a combination of seabed physical attributes and related organisms. To map seabed biotopes in deep water, remote sensing using a combination of acoustic, optical and physical sensors is investigated. The hypothesis tested in this thesis is that acoustic bathymetry and backscatter data from a Simrad EM1002 multi-beam sonar (MBS) can be used to infer (act as a surrogate of) seabed biotopes. To establish a link between the acoustic data and seabed biotopes the acoustic metrics are compared to the physical attributes of the seabed in terms of its substrate and geomorphology at the 10s m to 1 km scale using optical and physical sensors. At this scale the relationship between the dominant faunal functional groups and both the physical attributes of the seabed and the acoustic data is also tested. These tests use data collected from 14 regions and 2 biomes to the south of Australia during a voyage in 2000. Based on 62 reference sites of acoustic, video and physical samples, a significant relationship between ecological seabed terrain types and acoustic backscatter and bathymetry was observed.These ecological terrain types of soft-smooth, soft-rough, hard-smooth and hard-rough were chosen as they were the most relevant to the biota in their ability to attach on or burrow into the seabed. A seabed scattering model supported this empirical relationship and the overall shape of backscatter to incidence angle relationship for soft and hard seabed types. The correlation between acoustic data (backscatter mean and standard deviation) and the visual and physical samples was most consistent between soft-smooth and hard-rough terrain types for a large range of incidence angles (16o to 70o). Using phenomenological backscatter features segmented into 10 common incidence angle bins from -70o to 70o the length resolution of the data decreased to 0.55 times depth. The decreased resolution was offset by improved near normal incidence (0o to 30o) seabed type discrimination with cross validation error reducing from 32% to 4%. A significant relationship was also established between the acoustic data and the dominant functional groups of fauna. Faunal functional groups were based on the ecological function, feeding mode and substrate preference, with 8 out of the 10 groups predicted with 70% correctness by the four acoustically derived ecological terrain types. Restricting the terrain classification to simple soft and hard using the acoustic backscatter data improved the prediction of three faunal functional groups to greater than 80%. Combining the acoustic bathymetry and backscatter data an example region, Everard Canyon, was interpreted at a range of spatial scales and the ability to predict the preferred habitat of a stalked crinoid demonstrated.Seabed terrain of soft and hard was predicted from the acoustic backscatter data referenced to a common seabed incidence angle of 40o. This method of analysis was selected due to its combined properties of high spatial resolution, consistent between terrain discrimination at the widest range of incidence angles and consistent data quality checking at varying ranges. Based in part on the research reported in this thesis a mid-depth Simrad EM300 multibeam sonar was purchased for use in Australian waters. A sampling strategy is outlined to map all offshore waters with priority within the 100 m to 1500 m depths.
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Kloser, Rudolf J. "Seabed biotope characterisation based on acoustic sensing." Curtin University of Technology, Faculty of Science and Engineering, Department of Imaging and Applied Physics, 2007. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=18566.
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The background to this thesis is Australia’s Oceans Policy, which aims to develop an integrated and ecosystem-based approach to planning and management. An important part of this approach is the identification of natural regions in regional marine planning, for example by establishing marine protected areas for biodiversity conservation. These natural regions will need to be identified on a range of scales for different planning and management actions. The scale of the investigation reported in this thesis is applicable to spatial management at 1 km to 10 km scale and monitoring impacts at the 10s of m to 1 km biotope scale. Seabed biotopes represent a combination of seabed physical attributes and related organisms. To map seabed biotopes in deep water, remote sensing using a combination of acoustic, optical and physical sensors is investigated. The hypothesis tested in this thesis is that acoustic bathymetry and backscatter data from a Simrad EM1002 multi-beam sonar (MBS) can be used to infer (act as a surrogate of) seabed biotopes. To establish a link between the acoustic data and seabed biotopes the acoustic metrics are compared to the physical attributes of the seabed in terms of its substrate and geomorphology at the 10s m to 1 km scale using optical and physical sensors. At this scale the relationship between the dominant faunal functional groups and both the physical attributes of the seabed and the acoustic data is also tested. These tests use data collected from 14 regions and 2 biomes to the south of Australia during a voyage in 2000. Based on 62 reference sites of acoustic, video and physical samples, a significant relationship between ecological seabed terrain types and acoustic backscatter and bathymetry was observed.These ecological terrain types of soft-smooth, soft-rough, hard-smooth and hard-rough were chosen as they were the most relevant to the biota in their ability to attach on or burrow into the seabed. A seabed scattering model supported this empirical relationship and the overall shape of backscatter to incidence angle relationship for soft and hard seabed types. The correlation between acoustic data (backscatter mean and standard deviation) and the visual and physical samples was most consistent between soft-smooth and hard-rough terrain types for a large range of incidence angles (16o to 70o). Using phenomenological backscatter features segmented into 10 common incidence angle bins from -70o to 70o the length resolution of the data decreased to 0.55 times depth. The decreased resolution was offset by improved near normal incidence (0o to 30o) seabed type discrimination with cross validation error reducing from 32% to 4%. A significant relationship was also established between the acoustic data and the dominant functional groups of fauna. Faunal functional groups were based on the ecological function, feeding mode and substrate preference, with 8 out of the 10 groups predicted with 70% correctness by the four acoustically derived ecological terrain types. Restricting the terrain classification to simple soft and hard using the acoustic backscatter data improved the prediction of three faunal functional groups to greater than 80%. Combining the acoustic bathymetry and backscatter data an example region, Everard Canyon, was interpreted at a range of spatial scales and the ability to predict the preferred habitat of a stalked crinoid demonstrated.
Seabed terrain of soft and hard was predicted from the acoustic backscatter data referenced to a common seabed incidence angle of 40o. This method of analysis was selected due to its combined properties of high spatial resolution, consistent between terrain discrimination at the widest range of incidence angles and consistent data quality checking at varying ranges. Based in part on the research reported in this thesis a mid-depth Simrad EM300 multibeam sonar was purchased for use in Australian waters. A sampling strategy is outlined to map all offshore waters with priority within the 100 m to 1500 m depths.
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Mukherjee, Kalparupa. "Investigation into trapping mechanisms and impact on performances and reliability of GaN HEMTs through physical simulation and electro-optical characterization." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0401/document.
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Le Nitrure de Gallium est devenu un matériau incontournable pour le développement de dispositifs semi-conducteurs aux performances très supérieures aux composants silicium. L'immense potentiel du dispositif HEMT AlGaN / GaN provient du gaz d'électrons à haute densité et à forte mobilité formé au niveau de son hétéro-structure. Cependant, le fonctionnement sous champ électrique, température et conditions de stress élevés rend le dispositif vulnérable aux problèmes de fiabilité qui limitent son efficacité et sa durée de vie. Les pièges présents dans la structure, qui limitent la densité porteurs du canal et pénalisent la réponse du dispositif, constituent le facteur majeur déterminant plusieurs effets électriques parasites et la fiabilité du dispositif. L’industrie du GaN est confrontée à la nécessité de disposer de dispositifs de haute fiabilité si bien qu’il est nécessaire de faire des progrès dans l’analyse de l’impact des pièges pour en déduire des solutions technologiques permettant leur inhibition.La motivation de ce travail est d’identifier les signatures électriques associées à l’activité de différents pièges ainsi que leurs conséquences sur les performances et la fiabilité des HEMT GaN grâce à une étude dédiée des dispositifs de la technologie GH-25 conçue pour des applications RF de puissance fonctionnant jusqu’à 20 GHz. L’étude utilise des simulations physiques TCAD. Une analyse détaillée des effets indépendants et interdépendants est réalisée afin d'identifier l'impact relatif des pièges pour des études de cas où les caractéristiques électriques présentent des écarts importants par rapport à la réponse idéale du dispositif.La méthodologie utilisée pour développer un modèle TCAD représentatif et dérivé de la physique interne est décrite en accordant une attention particulière au courant de fuite de grille qui reflète l'influence de processus physiques fondamentaux ainsi que les effets parasites couramment rencontrés dans les dispositifs GaN. Les simulations ciblées établissent un lien entre l'observation d'un problème de fiabilité et son origine sous-jacente dans les phénomènes de piégeage.L’établissement d’associations entre la localisation spatiale des pièges et les dégradations qu’ils pourraient provoquer est un objectif important de cette thèse.Plusieurs stratégies de simulation sont présentées, permettant d’explorer le comportement des pièges en régime permanent et en régime transitoire et donnant une perception détaillée de la manière dont les paramètres des pièges affectent les caractéristiques opérationnelles. Des approches pour distinguer les interactions de pièges différents sont également décrites. L’étude centrale de cette thèse est un phénomène de courant de fuite parasite complexe, identifié dans le procédé GH 25comme conséquence du vieillissement accéléré. Connu sous le nom de «belly-shape», il représente un exemple intéressant de la façon dont les stratégies développées peuvent être appliquées pour discerner la causalité, l'impact et l'évolution des pièges responsables du phénomène. Afin d'approfondir l'analyse des modes de piégeage, nous avons procédé à des tests de vieillissement accéléré et des caractérisations électro-optiques afin de modifier la dynamique générale du mécanisme de piégeage et d'observer la modulation du mécanisme du piégeage sur la réponse du dispositifGallium Nitride has emerged as a terrific contender to lead the future of the semiconductor industry beyond the performance limits of silicon.The immense potential of the AlGaN/GaN HEMT device is derived from the high density, high mobility electron gas formed at its hetero-structure. However, frequent subjection to high electric field, temperature and stress conditions makes the device vulnerable to reliability issues that restrict its efficiency and life time. A dominant contributor to several parasitic and reliability issues are traps present within the semiconductor structure which restrict the channel density and aggravate the device static and dynamic response. As the GaN industry addresses an increasing demand for superior devices, reliability analysis is of critical importance. There is a necessity to enable advancements in trap inhibition which would allow the realization of stronger, efficient devices.The motivation of this work is to recognize distinct ways in which various traps affect the performance and reliability metrics of GaN 0.25 µm HEMTs through a study of devices of the GH-25 process optimized for high power applications up to 20 GHz. The investigation employs physical TCAD simulations to provide insight and perspective to electrical and optical characterizations. Detailed analysis into independent and interrelated effects is performed to identify the relative impact of traps in circumstances presenting notable deviations from the ideal device response.The methodology to develop a representative TCAD model derived closely from internal physics is described with special focus on the sensitive gate leakage characteristic which reflects the influence of fundamental physical processes as well as parasitic effects commonly encountered in GaN HEMTs. Targeted simulations provide a pivotal link between the observation of a reliability issue and its underlying origin in trapping phenomena. Establishing associations between the spatial location of traps and the degradations they could trigger is an important objective of this thesis.Several simulation strategies that explore trapping behavior in various steady state and transient environments are discussed which allow detailed perception into the manner and extent to which trap attributes affect operational considerations. Approaches to distinguish disparate trap interactions are also described. The central case study in this thesis is an abstruse parasitic leakage phenomenon, identified in the GH 25 process as a consequence of aging stress. Referred to as the “belly shape”, it presents an interesting example of how the developed strategies can be applied to discern the causality, impact and evolution of the responsible traps. In order to take a deeper look into trapping modes, further aging and LASER characterizations are performed to alter the general occupational dynamics and observe the modulation of trap control over device response
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RADIS, MICHELA. "Influence of material optical characteristics on vision and fruition of Cultural Heritage." Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2687256.
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For Cultural Heritage materials is important to guarantee a correct conservation and vision of the artefacts, enhancing the observer experience assuring the best visual and conceptual appearance of artefacts. Several factors affect the visual appearance of artistic materials. However, available measurement methodologies for the material characterisation are not able to accurately predict the visual appearance of materials usually used in cultural heritage.
Goals of the thesis research was to identify the visual attributes that mainly affect the appearance of artworks, investigate the correlation between measured data and visual human response and individuate if there are measured conditions that allow a better correlation. Finally, provide useful suggestion to aid in planning and selecting adequate conservative intervention, such as restoration work. In order to reach these purposes, different samples representative of materials used in artistic artefacts were selected and realised and two different visual testes were set up and carried out investigating the influence of lighting and viewing conditions on the human visual response of selected visual attributes: glossiness, colour (saturation), brightness and sparkling. The first visual test takes into account how the human visual responses on glossiness and saturation are affected by the lighting and viewing conditions using coloured samples with different levels of gloss obtained brushed on them different mixture of natural varnishes. While, in the second visual test were identified the elements that mainly affect the human perception of sparkling and brightness in monochromatic samples with mica particles, a mineral easily found in ornamental stones. At the end of each visual test, all responses were statistical analysed and, then, the results were compared with the corresponding objective measured data. In this way, it was possible to define what measurement conditions allow to have a better correlation with the subjective assessment.
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Morris, Iestyn L. "Optical characterisation of semiconductors." Thesis, Aberystwyth University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386969.
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Fitzmaurice, Anthony J. "Characterisation of nonlinear optical materials." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240597.
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Fermann, Martin. "Characterisation techniques for special optical fibres." Thesis, University of Southampton, 1988. https://eprints.soton.ac.uk/404728/.
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Special optical fibres are introduced with the emphasis on rare-earth-doped fibres and fibres with crystal-like properties. Characterisation techniques for these types of fibre are discussed and several applications are described. In particular, optical time-domain reflectometry is used to demonstrate a distributed temperature sensor based on the temperature dependence of the absorption in rare-earth-doped fibres. Further, energy transfer between ytterbium and erbium is characterised and an erbium fibre laser sensitised with ytterbium is demonstrated. Finally, techniques for the creation of crystal-like properties in optical fibres are developed and second-order nonlinear phenomena in these fibres are analysed both experimentally and theoretically.
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Hillman, Christopher Wyndham John. "Scanning near-field optical microscope characterisation of microstructured optical fibre devices." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/15484/.
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This thesis details work relating to the characterisation of microstructured fibres using SPM techniques. More specifically the optical properties of the fibres have been investigated by the use of a scanning near-field optical microscope and atomic force microscopy. The SNOM was constructed and fully characterised as part of this work. The current state of research into microstructured fibre fabrication, theory and applications is currently benefitting from a great deal of interest from academia and commercial investors alike. New fibre structures are being produced at a rate previously impossible. With this increase comes a need to be able to characterise more effectively the fibres that are produced. SNOM provides a number of significant features that address this issue. In this work four recently fabricated microstructured fibres have been investigated at a number of wavelengths. In each case accurate mode pro- files have been measured and compared with resolution that would be extremely difficult to obtain with traditional mode profiling techniques. A theoretical model has also been used to predict the mode profiles. Measurements of the mode profiles after propagation in free space are presented and are compared to a theoretical beam propagation technique. An interferometric technique at 1550nm was used to image electric field amplitude and phase of the fibre modes, including results on the phase evolution of the mode as it propagates in free space.
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Xu, Jiansheng. "Characterisation and magneto-optical enhancement of thin film TbFeCo." Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317538.
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Acreman, Andrew. "Gold nanoparticle liquid crystal composites : synthesis, characterisation and optical nonlinearities." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/379319/.
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This thesis presents a theoretical and experiment investigation into the optical properties of gold nanoparticle liquid crystal composites. The experimental work can be divided into four sections; the synthesis of the nanoparticles, the creation of the gold nanoparticle liquid crystal composites and the investigation into their electro-optical properties and the nonlinear properties of hybrid photoconductive cells. A large variety of gold nanoparticles were chemically synthesised with varying size distributions and functionalized. The samples functionalized with chemicals containing aromatic chemical groups were observed to aggregate. The optical properties of these aggregates were investigated by measuring their absorption and scattering efficiencies. The samples displayed a decrease in their molar absorption coefficient from 10 cm⁻¹μM⁻¹ to 4.61 cm⁻¹μM⁻¹ and an increase in the molar scattering coefficient by several orders of magnitude. Gold nanoparticles were also synthesised directly in the liquid crystal host by sputter doping. In this case it was found that the size of these particles could be increased by heating the host liquid crystal above the clearing temperature of the liquid crystal. The synthesised nanoparticles as well as samples from other groups were used to produce gold nanoparticles liquid crystal composites. With the exception of one sample functionalized with mesogenic compounds all of the samples displayed a solubility lower that the samples synthesised by sputtering indicating that, unless carefully selected, the thiol surfactants were detrimental to the solubility of the nanoparticles in a liquid crystal. Four samples, a pure liquid crystal and three doped with low concentrations (0.01% by weight) of gold nanoparticles were used to fill hybrid photoconductive cells. Two of the samples, made from comparatively larger, less soluble, nanoparticles displayed a dramatic increase in the nonlinearity of over an order of magnitude in comparison to the undoped liquid crystal. While previous work has illustrated that ferro-electric nanoparticles can lead to a similar increase in the nonlinearities, however these can be attributed to increases in the display parameters of the host liquid crystal. A electro-optic characteristics of the gold nanoparticle samples showed no such increase. The two samples which displayed an increase in the nonlinearity also displayed a substantial increase in the conductivity, and consistently it was concluded that this was the cause of the increase in the nonlinearity. The theoretical section of the thesis models thermal nonlinearities which could be observed in high concentration liquid crystal gold nanoparticle composites. By considering the attenuation of the pump and probe beams throughout the cell and the effect that this has on the thermal profile within the cell an excellent agreement with experimental data was achieved. The model further predicted that due to this attenuation there exists an optimum concentration of absorbents. The model was further extended to consider the effect of a magnetic field induced reorientation of the liquid crystal. This adaptation accounted for the thermal change in the diamagnetic anisotropy and elastic constants as well as the change in the thermal refractive index grating and absorption of the nanoparticles due to the reorientation of the liquid crystal. The reorientation caused a decrease in the magnitude of the refractive index grating from 9x10⁻⁵ cm²W⁻¹ to zero by the application of a magnetic field of the order of 0.01 Tesla. If the field was further increased the medium would switch from a self-defocusing to a self-focusing regime.
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Jefferies, G. "The optical characterisation of nonlinear Langmuir-Blodgett film forming materials." Thesis, Cranfield University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282440.
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Lochran, Stephen. "An optical, electro optic and thermal characterisation of various organic crystals." Thesis, University of Strathclyde, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249852.
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Rees, Peter. "Characterisation of the waveguide dependence of optical mode loss in semiconductor lasers." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/108204/.
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The improvement of optical mode loss in semiconductor lasers is of significant commercial value, contributing to lower threshold current densities and higher above-threshold slope efficiencies. While it has improved significantly with successive developments in semiconductor laser design resulting from improvements to the fabrication process, characterisation methods for the measurement of optical mode loss have not kept pace. Today values of optical mode losses as low as 1cm-1 are frequently reported, and yet the precision and accuracy of its measurement are rarely better than 1cm-1 itself. To address this, I demonstrate that a modulated approach to the segmented contact method for the measurement of modal absorption and loss can measure optical mode losses with precisions as low as 0.1cm-1. I also demonstrate the removal of non-linearity from detection system using a novel approach to amplitude calibration by flux superposition. I apply this improved methodology in the comparison of InAs QD samples with differing waveguide core dimensions (2440Ǻ and 3740Ǻ), finding a reduction in optical mode loss between these samples from (4.8±0.4)cm-1 to (2.25±0.10)cm-1. In addition to measuring the optical mode loss at the lasing wavelength I investigated the origins of the observed wavelength dependence of optical mode loss below the material band-edge, comparing experimental values of modal absorption and loss spectra with a waveguide model. I show the wavelength dependent optical mode loss of wide waveguide core samples agrees well with losses predicted from model incorporating free carrier absorption, intervalence band absorption and waveguide dispersion. I also show that in both samples optical mode losses and their respective wavelength dependences are insensitive to changes in temperature from 298-370K. I also investigate the causes of oscillating modal absorption and loss seen in narrow waveguide core samples.
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Roelens, Michaël Alberic Freddy. "Precise intensity and phase characterisation of optical telecommunication signals." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/42380/.
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In this thesis, the accurate characterisation of a range of high speed optical telecommunication signals is presented. The main technique used to determine both the intensity and the phase profiles of these signals is based on spectrograms, and various developments and extensions of this method are presented. Finally, data modulated pulses in a 40 Gbit/s system are characterised before and after propagation in an installed fibre link, and excellent agreement is found between the information retrieved from the spectrogram method, independent intensity measurements and theoretical expectations.
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Gordon, Neil Andrew. "Characterisation and control of coupled optical springs for future gravitational wave detectors." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6532/.
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The detection of gravitational waves in the years to come will be the result of decades of work by institutions around the world to design and construct instruments to probe the characteristic strain of space-time on the smallest scales. Once detected, an entirely new field of study will be open to astronomy, allowing probing of the interior structure of massive celestial objects and insight into the very beginning of the universe. However, this will by no means signal the end of this work. Efforts will continue to push the sensitivity limits of detectors ever lower, at the same time widening our gravitational wave horizon to encompass sources at greater distances. Soon, gravitational wave detectors are expected to be operating at the Standard Quantum Limit throughout much of their detection bandwidth. Novel techniques will need to be employed to probe beneath this level. One such method involves the use of opto-mechanical rigidity, or "optical springs". This technique couples the suspended optics of a Fabry-Pérot cavity together using only the radiation pressure force transferred between them, transforming the system into the harmonic oscillator regime and thus increasing sensitivity in a narrow band about the associated resonance. If this technique is to be applied to a large-scale gravitational wave detector, the effect must be well-characterised and robust control methods investigated. Importantly, the optical spring effect is observed to arise in any gravitational wave detector operating with high power, providing further motivation for the study of control systems to cope with them. It has further been suggested that multiple optical springs may be employed in a single system, either for improved optical stability such that electronic feedback may be reduced, or else to favourably re-shape the noise spectrum of the instrument for wider-band sensitivity improvement. We present the design and commissioning of an experiment at the Glasgow 10m Prototype Interferometer Laboratory to investigate characterisation and control methods for coupled optical spring systems. The experimental system consists of two 10m cavities coupled mechanically by a shared end test mass. Each cavity can be detuned to facilitate opto-mechanical coupling, the combined effects of which are studied. The design of this experiment is covered from initial simulations through mechanical design, testing and installation. Robust digital control loops are built, providing techniques for reliable lock-acquisition of high-finesse optical cavities and maintenance of stability in the presence of strong opto-mechanical effects. A number of experiments are performed to examine the interactions between optical springs in both cavities and the control loops which maintain them. We observe marked power stability over significant periods of time to enable precision measurement of optical spring resonant responses in both cavities, and confirm the power-dependence of the optical spring effect. Techniques are described for the maintenance of stable cavity lock in the presence of strong optical springs and anti-springs, and complex responses resulting from couplings of multiple springs to loop gains are characterised. This work will inform the design of future gravitational wave detectors, which are expected to employ optical spring technologies in order to push further beneath the Standard Quantum Limit.
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Finnan, Craig James. "The growth and characterisation of crystalline photoreactive materials for optical limiting applications." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288603.
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Andersson, Kent. "Preparation and Characterisation of Sputtered Titanium- and Zirconium Nitride Optical Films." Licentiate thesis, Solid State Physics Group, Department of Technology, Uppsala University, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:fhs:diva-4530.
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Multilayered interference coatings based on titanium- and zirconium nitride and designed for solar control have been prepared using reactive d c magnetron sputtering. Preparation effects and degradation mechanisms were investigated. It was shown that the quality of the nitride strongly depends on the degree of crystallinity in the underlying oxide. It has been shown that the nitride layer partly oxidizes as the top oxide layer is deposited. The degradation is enhanced with temperature. A thin sacrificial layer of aluminium deposited between successive depositions of nitride and oxide is shown to improve the optical performance of the coating as preparedm as well as after accelerated ageing tests. The optical properties of opaque and semitransparent films of zirconium nitride have been studied. A thorough investigation of the influence of composition, deposition rate, substrate temperature and film thickness on the optical response of the film was performed. Both photometric and ellipsometric methods were used to determine thicknesses and the optical constants at wavelengths ranging from 0.23 to 25 μm. The resulting values of n and k, in the wavelength intervals where these independent methods are applicable, have been shown to agree extremely well. The results so far indicate an even larger potential for zirconium nitride based solar control coatings as compared to the titanium nitride based. Access to optical constants derived from films of zirconium nitride of variable quality made multilayer modelling a powerful tool in the design and analysis of solar control coatings.
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Aesa, Abdulsattar Ahmad. "Characterisation of laser processed bio-compatible materials and the realisation of electro optical diffraction gratings." Thesis, University of Hull, 2018. http://hydra.hull.ac.uk/resources/hull:16591.
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Laser processing methods using excimer lasers have become very attractive for processing materials and the fabrication of micro and nano optical components. Diffraction gratings are used in a wide range of applications and require different fabrication methods. These components can be fabricated from a variety of biocompatible polymers. In this work, an Argon Fluoride (ArF) excimer laser operating at a wavelength of 193 nm has been used to process chitosan and agarose substrates. These materials have been characterised for differing laser processing conditions. Diffraction gratings and component demonstrators have been realised using Laser Direct writing (LDW) and nanoimprinting lithography (NIL). Characterisation of the ArF 193 nm laser work involves ablation threshold, optical absorption measurements and quantification of structural and morphological changes. This results can be used to identify the ideal laser fluence to be used for the production of a diffraction grating and similar optical components fabricated from chitosan. An ablation threshold of chitosan at 193 nm wavelength has been measured as 85 mJcm−2 and an optical absorption coefficient of 3×103 cm−1. A diffraction grating structure, measuring 12 μm, was generated in biocompatible materials films; chitosan and agarose, using a laser processing method. The results showed that the interaction between the laser and these materials can potentially open the pathway for a wide range of practical, real world applications such as optical and biomedical applications. Diffraction gratings with a feature size of 1 μm were successfully formed on the biocompatible material free standing films using a NIL technique. Microstructure cross grating patterning made of chitosan and agarose have been fabricated by ArF excimer laser processing using a mask projection ablation technique. Temperature rise calculations have been carried out by COMSOLTM Multi-Physics v5.3 using a Finite Element Method (FEM), to predict the temperature rise during laser ablation processing of chitosan and agarose. In addition, COMSOLTM Multi-physics v5.3 has been used to simulate the electric field in the vicinity of a diffraction grating that is illuminated with light from a HeNe laser emitting at a wavelength of 632.8 nm. The final experimental work investigated the possibility of realising 5CB liquid crystal doped chitosan diffraction gratings doped with Sudan Black B (SBB) dye to enhance the absorption properties at 632.8 nm. Diffraction gratings was fabricated using two intersecting beams from a HeNe laser. Polymer Dispersed Liquid Crystal (PDLC) chitosan doped with 5CB and SBB dye diffraction gratings were experimentally characterised.
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Gill, Devinder Singh. "Fabrication and characterisation of thin film optical waveguides by pulsed laser deposition." Thesis, University of Southampton, 1996. https://eprints.soton.ac.uk/398737/.
Full textAbstract:
This thesis describes 3 years research on the fabrication and characterisation of thin film optical waveguides using the pulsed laser deposition technique. Optical waveguides have many advantages over their bulk counterparts due to the high intensity-length product that can be achieved by tight beam confinement in a waveguide mode. These waveguides can also form the key elements necessary for assembling a complete thin-film optical integrated circuit. The thin films were deposited in a vacuum chamber that was designed and built in the first 6 months of the research program, at the Department of Physics, Southampton University. The chamber was equipped with several novel designs such as a target manipulation mechanism that enabled many films to be grown from a single target, and a CO2 laser for substrate heating which proved intrinsically cleaner and more efficient than conventional heating methods. The crystal structure of the films was investigated using x-ray diffraction techniques and the chemical composition was determined by Rutherford backscattering spectroscopy and energy-dispersive x-ray analysis. Crystalline and stoichiometric KNbO3 thin film optical waveguides were fabricated onto heated MgO substrates, for the first time, using pulsed laser deposition. The chemical composition and deposition rate of the films were measured as a function of the oxygen partial pressure, excimer laser fluence, substrate temperature and target-substrate distance. For this material only, it was necessary to use a potassium enriched ceramic target to compensate for the potassium deficiency in the films. Amorphous thin films of the chalcogenide glass, Ga-La-S were deposited onto CaF2 and glass substrates at room temperature. The refractive indices of the films were measured using the dark-mode prism coupling technique and the values were dependent on the excimer laser fluence. The photosensitive properties of the films were investigated and shown to induce a permanent refractive index change as large as -1%. On the basis of these results, grating structures were fabricated on the surface of the films using both laser and e-beam addressing. Finally, a crystalline layer of neodymium doped Gd3Ga5O12 was deposited onto a heated Y3Al5012, substrate. The waveguide lased at ~1.06µm when pumped with light from a Ti:sapphire laser at 808nm. This is the first ever lasing result from a waveguide structure that has been fabricated by pulsed laser deposition.
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Steer, Brian. "Selective characterisation of engineered nanoparticles in aerosols using nucleation and optical techniques." Thesis, University of Kent, 2014. https://kar.kent.ac.uk/48699/.
Full textAbstract:
The aim of this project is to develop novel approaches for the detection and characterisation of engineered and other potentially harmful nanoparticles in the air. In particular we wish to distinguish specific nanomaterials from the background atmospheric aerosol to provide a means of measuring human exposure to nanomaterials that may present a risk to health. Ideally, solutions should be practically deployable in the field. The metrics considered for measurement across this project are: size, number, chemical nature and surface area. Two main approaches are chosen to address these requirements: online size selective surface area controlled nucleation, and quantitative assessment of size resolved Raman spectroscopic maps. The first approach is based on the discovery of a different regime type of heterogeneous nucleation. In this case nucleation probability is determined by the surface area of the aerosol rather than the number of nuclei present. A portable DMA has also been developed allowing for the pre-separation of particles according to size in a compact package. Combining this DMA with the novel nucleation technology provides a means of measuring surface area distributions of particles. Finally, a novel Raman spectroscopic methodology is presented for the chemically specific quantification of aerodynamically size selected samples. Particles are first aerodynamically size segregated from the air in a wide size range sampler. These size fractionated samples are analysed by Raman spectroscopy. Imaging analysis is then applied to Raman spatial maps to provide chemically specific quantification against the substrate as a proxy for background aerosol. Analysing this data in combination with the known deposition efficiency of aerosols in the respiratory tract (provided by the sampling method), can then provide a complete exposure measurement approach.
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McCoy, Anoma Dayawansa. "Intensity noise suppression using a semiconductor optical amplifier : characterisations and applications." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/65501/.
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In this thesis I present a comprehensive system-level study of the intensity noise suppression offered by a saturated semiconductor optical amplifier (SOA), and its application to high channel count spectrum-sliced and optical code division multiplexed (OCDMA) systems incorporating low-cost incoherent light sources. Preliminary investigations into incorporating a saturated SOA to reduce low frequency noise of a highly coherent fibre distributed feedback laser are also presented.
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Steer, Matthew John. "Optical and structural characterisation of III-V semiconductor qauntum wire and quantum dot structures." Thesis, University of Sheffield, 1998. http://etheses.whiterose.ac.uk/3458/.
Full textAbstract:
This thesis describes an extensive study of the optical and structural properties of GaAs/AlGaAs V-groove quantum wire and InAs/GaAs self-organised quantum dot structures. For the optical characterisation, the spectroscopic techniques of photoluminescence (PL), photoluminescence excitation (PLE), cathodoluminescence (CL) and electroluminescence (EL) have been used. In addition important information concerning the structural properties of the quantum wires and quantum dots has been obtained by high resolution transmission electron microscopy (TEM) measurements. Initial characterisation and optimisation of the quantum wire structures was conducted using CL and TEM imaging. Further optical characterisation of optimised structures was performed using a micro-focusing PL set-up which produced a laser spot size of -'2µm, allowing individual wires to be studied. Excitation under both high and low power density conditions revealed important information concerning the quality of the growth and the nature of the one-dimensional` confinement within the structure. Structures were grown with the quantum wires placed in the intrinsic region of a p-i-n junction. EL spectroscopy measurements allowed the observation of subband filling effects and an enhanced luminescence intensity for the quantum wire for low forward bias currents. This latter behaviour has important implications for device applications. An investigation of these p-i-n samples in magnetic fields up to 14T, revealed further evidence for 1D confinement in the quantum wires and 2D confinement of carriers in a vertical quantum well. This vertical quantum well, a feature that arises automatically during the growth, appears to channel carriers into the quantum wire, providing a possible mechanism for the enhanced wire electroluminescence intensity observed. In addition, evidence is presented for a possible excitonic-free carrier transition which is observed for high carrier densities in the wires. TEM structural analysis of self-organised InAs/GaAs quantum dots has shown that the dots can show a high degree of surface ordering, aligning themselves on the step edges of the underlying substrate. Excitation under high laser power densities using the micro-PL set-up has shown subband separations of around 75meV, which is very promising for room temperature opto-electronic device applications. In addition, very narrow line width emission has been observed from individual quantum dots on a small sub-micron etched mesa which contains -100 dots. The electronic structure of the quantum dots has been probed using resonant PL and PLE. These techniques have revealed important information regarding carrier relaxation mechanisms that exist in the quantum dots. In PLE features are observed at approximately 60 and 90meV from the detection energy and which move rigidly in energy when the detection energy is varied. This behaviour is attributed to carrier relaxation by the emission of multiple LO- phonons, a process that appears to bypass any `phonon bottleneck'. Similar features are also observed in resonantly excited PL spectra. Two distinct carrier relaxation mechanisms are demonstrated by this technique: a non-resonant mechanism from the upper excited state and a resonant mechanism involving the emission of multiple LO phonons, from the first excited state.
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Gregory, Tiffany Jane. "Optical characterisation and Zeeman studies of dilute magnetic single layer and multiple quantum well structures." Thesis, University of Hull, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305914.
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Vienne, Guillaume. "Fabrication and characterisation of ytterbium:erbium codoped phosphosilicate fibres for optical amplifiers and lasers." Thesis, University of Southampton, 1997. https://eprints.soton.ac.uk/394566/.
Full textAbstract:
This thesis deals with the fabrication, characterisation, and applications of ytterbium: erbium codoped fibres. The fibres are fabricated by modified chemical vapour deposition (MCVD) combined with the solution doping technique. The properties of phosphate glasses are reviewed and we show that the fabrication process must be adapted to cope with the low viscosity of the phosphate glass. We identify the three major pitfalls which initially plagued the fabrication process and show how they can be avoided. We also describe how all glass double-clad fibres can be fabricated. The composition of the core glass is measured by energy dispersive X-ray spectrometry and inductively coupled plasma mass spectrometry. The latter technique offers sufficient accuracy to evaluate erbium and ytterbium absorption cross-sections. Raman and infrared spectroscopy are also used to gain insight into the structure of the glass. Techniques to evaluate the suitability of our fibres for efficient devices are presented and some loss mechanisms are investigated. Addition of aluminium to Er/Yb codoped phosphosilicate fibres in the region [Al]<[P] is studied for the first time to our knowledge. We show that the ternary Al/P/Si system is not a simple juxtaposition of the binary Al/Si and P/Si systems. Nevertheless, we find evidence that the rare-earths remain essentially coupled to phosphate sites for the region [Al] < [P], although addition of aluminium still appears to reduce rare-earth clustering. Finally, we present a model of Er/Yb devices based on the formalism of the rate equations, and give examples of how it can be useful to predict the effect of modifications in fibre design. To conclude we present the devices which have benefited from this work, particularly single frequency grating feedback lasers and cladding pumped lasers.
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Wilkie, Stuart. "The preparation and optical characterisation of novel organic crystals with applications in non linear devices." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248563.
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Reich, Daniel Maximillian [Verfasser]. "Efficient Characterisation and Optimal Control of Open Quantum Systems - Mathematical Foundations and Physical Applications / Daniel Maximillian Reich." Kassel : Universitätsbibliothek Kassel, 2015. http://d-nb.info/1073888851/34.
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Zachmann, Nils. "Characterisation of a Gas Modulation Refractometer for Detection of Gases at 1550 nm." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-148557.
Full textAbstract:
Only very few molar polarizabilities are known with high accuracy; and when so, they are in general only known at a given wavelength. There is therefore a need to assess the molar polarizability with high accuracy of various gases, at different wavelengths. The molar polarizability of a gas is a measure of the susceptibility of a molecule to have its charge distribution affected by light. It is also the entity that relates the index of refraction to the (molar) density of a gas in Lorentz-Lorenz equation. Hence, for high precision measurements of the density of a gas, it is important to know the molar polarizability of the gas to high accuracy. In this work a GAMOR system has been used to determine the wavelength-dependent molar polarizability of Ar at 1550 nm. However, a high accuracy assessment of the molar polarizability of a gas requires that the gas density is known with high accuracy. Since this is not trivial to assess, the molar polarizability of argon has been assessed in terms of that of nitrogen, which is assumed to be known with high accuracy. Hence, to minimise measurement errors, the measurement cavity was alternately filled with nitrogen and argon and the ratio between the signals provided by the GAMOR system represents the ratio of the molar polarizabilities of the two gases. It was found that the molar polarizability of argon was 0.94393(5) times that of nitrogen. Since the latter one has been assessed to 4.34828(3) x 10^-6 m^/mol, the molar polarizability of argon could be assessed to 4.10446(5) x 10^-6 m^3/mol.
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Mang, Matthias M. "Interferometric spatio-temporal characterisation of ultrashort light pulses." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:163c5374-1466-4c4d-a0f5-c4e66b27e2ac.
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The main topic of this thesis is the development of novel diagnostics for the characterisation of infrared femtosecond and extreme-ultraviolet (XUV) attosecond pulses. High-resolution interferometric methods are applied to high harmonic radiation, both to measure the properties of the XUV light and to relate this information to the physics of the fundamental generation process. To do so, a complete high harmonic beamline has been built and optimised to enable the observation of strong signatures of the macroscopic response of the medium. The distinct spatial characteristics of long and short trajectories are studied, as well as the interference between them. An interferometric measurement allows the extraction of the atomic dipole phase, which gives direct access to the sub-cycle electron dynamics. A major focus of this thesis is on the development of a novel method which simultaneously characterises two independent electric fields as a function of any degree of freedom in which it is possible to shear one of the beams. Since each field alternately takes the role of the reference to retrieve the other field, this technique is referred to as mutual interferometric characterisation of electric-fields (MICE). One of the key features of MICE is that no sheared but otherwise identical replica of the test pulse needs to be generated, which is a typical requirement of self-referencing techniques. Furthermore, no a priori information is needed for the reconstruction. The strength and the wide applicability of MICE are demonstrated using two fundamentally different examples. First, the temporal pulse profiles of two infrared femtosecond pulses are simultaneously reconstructed in a single laser shot. In the second demonstration, the MICE approach is used to simultaneously reconstruct the wavefronts of two high harmonic beams. Having this new technique at hand, the phase properties of the different quantum trajectories are compared. All pulse characterisation techniques implicitly assume full coherence of the beam. This, however, is often not the case in practice, in particular when dealing with complex XUV light sources. Here the standard characterisation techniques fail to provide an accurate description of the electric field. Instead, the electric field must be seen as a statistical mixture of different contributions to the overall field. Here an interferometric experiment is first proposed and then performed involving multiple lateral shears to measure the two-point correlation function of high harmonic radiation. This directly provides information about the existence and the magnitude of partial coherence of high harmonics.
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Senior, Roger J. "Microwave Frequency Characterisation of Squeezed Light From an Optical Parametric Oscillator." Thesis, 2006. http://hdl.handle.net/1885/44519.
Full textAbstract:
The quantum statistics of a laser result in noise when measurements of the beam are
made. This noise sets a classical limit beyond which a laser cannot be used with increasing
sensitivity. This quantum noise limit is imposed on many of the uses of lasers currently,
especially in power limited devices such as optical communications. The statistics of the
laser photon field can be modified to produce a non-classical state resulting in lower noise
than the quantum noise limit when detected appropriately. This state, called a squeezed
state, has been measured previously from a cavity enhanced optical parametric oscillator
(OPO) only at frequency sidebands within the linewidth of the cavity.
¶
This thesis reports measurements of squeezing at microwave frequency sidebands on
an optical beam produced by an optical parametric oscillator. This is the first reported
measurement of squeezing at frequency sidebands at higher longitudinal modes of the
cavity from an OPO. Noise reduction below the quantum noise limit is measured at sideband
frequencies of 5 MHz, 1.7 GHz, 3.4 GHz and 5.1 GHz, corresponding to the zeroth,
first, second and third longitudinal modes from the squeezed beam. These results are the
highest frequency sideband measurements of squeezing to date. In addition to measuring
squeezing at different longitudinal modes for the fundamental Gaussian spatial mode,
non-classical noise reduction is measured at the same frequencies for a squeezed higher
order spatial mode, TEM10.
¶
A single mode theoretical model of the OPO is presented, based on the work of ref.
[1]. Computer simulations of the squeezing predicted by this model are developed and
compared to the experimental results, showing excellent agreement between the different
longitudinal modes for each of the two spatial modes measured.
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Dragomir, Nicoleta. "Microscopic characterisation of photonic devices." Thesis, 2004. https://vuir.vu.edu.au/15522/.
Full textAbstract:
The work presented in this thesis sets out to explore the optical properties of optical fibres by means of non-invasive microscopic techniques such as Differential Interference Contrast (DIC) microscopy. It seeks to provide the fibre optic industrial and research community with an alternative tool that is cost effective, having the accuracy and robustness of the existing techniques in addition to being non-destructive relative to the optical fibre. The development of non-invasive microscopic imaging methods for exploring the physical properties of optical fibres is essential as alternative methods to the well-known standard ones that are often destructive.
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Kouskousis, Betty. "Microscopic characterisation of fibre Bragg gratings." Thesis, 2009. https://vuir.vu.edu.au/15498/.
Full textAbstract:
The focus of this thesis is the study of microscopic characterization of optical fibres and fibre Bragg gratings, by the use of a non-invasive microscopic technique, namely differential interference contrast microscopy. The thesis aims to provide detailed information on the structural and optical properties of optical fibres and fibre Bragg gratings. Furthermore, the thesis provides researchers with a new tool in the determination of various specimen parameters such as phase and refractive index distribution.
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(8407140), Saadia T. Chaudhry. "CHAIN-LENGTH PROPERTIES OF CONJUGATED SYSTEMS: STRUCTURE, CONFORMATION, AND REDOX CHEMISTRY." Thesis, 2021.
Find full textAbstract:
The development of solution-processable semiconducting polymers has brought mankind’s long-sought dream of plastic electronics to fruition. Their potential in the manufacturing of lightweight, flexible yet robust, and biocompatible electronics has spurred their use in organic transistors, photovoltaics, electrochromic devices, batteries, and sensors for wearable electronics. Yet, despite the successful engineering of semiconducting polymers, we do not fully understand their molecular behavior and how it influences their doping (oxidation/reduction) properties. This is especially true for donor-acceptor (D-A) p-systems which have proven to be very efficient at tuning the electronic properties of organic semiconductors. Historically, chain-length dependent studies have been essential in uncovering the relationship between the molecular structure and polymer properties. Discussed here is the systematic investigation of a complete D-A molecular series composed of monodispersed and well-defined conjugated molecules ranging from oligomer (n=3-21) to polymer scale lengths. Structure-property relationships are established between the molecular structure, chain conformation, and redox-active opto-electronic properties for the molecular series in solution. This research reveals a rod-to-coil transition at the 15 unit chain length, or 4500 Da, in solution. The redox-active optical and electronic properties are investigated as a function of increasing chain-length, giving insight into the nature of charge carriers in a D-A conjugated system. This research aids in understanding the solution behavior of conjugated organic materials.
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Petreski, Bill Petar. "Characterisation of optical fibre amplifiers: amplifiers for the 632.8 nm He-Ne wavelength in praseodymium-doped ZBLAN." Thesis, 1997. https://vuir.vu.edu.au/15750/.
Full textAbstract:
An investigation of small-signal amplification on the 3Po-3F2 transition in a praseodymium-doped fluorozirconate optical fibre at the 632.8 nm He-Ne wavelength, has been conducted. The optical gain is fundamentally related to the
spectroscopic characteristics of praseodymium-doped in a fluorozirconate glass host together with optical fibre parameters, that determine the physical characteristics of
the waveguide. These parameters have been experimentally determined independently of the gain and used to model the performance of the amplifier.