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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Spectral response modelling and analysis of heterojunction bipolar phototransistors

Khan, Hassan January 2010 (has links)
The optoelectronics industry continues to demand improved materials, devices and systems for the generation, transmission, detection, amplification and processing of optical signals. Heterojunction phototransistors (HPTs), in recent years, have attracted considerable interest for optical detection due to their intrinsic gain, low noise performance, high-frequency operation and process and the device layer compatibility with heterojunction bipolar transistors for high-speed optoelectronic monolithic microwave/millimetre-wave integrated circuit (OEMMIC) photoreceivers. A key performance parameter of HPTs is their spectral response (SR) which is critical in their usage in optical applications. The SR depends on several inherent factors including material absorption coefficient, refractive index, device structure, doping and temperature of operation along with the external factors such as bias voltage and the energy of incident radiation. The spectral response and optical characteristics of GaAs-based and InP-based sHPTs have been successfully predicted for the first time through an advanced absorption theoretical model. The model is based on the accurate prediction of photocarriers in the active layers of the phototransistor which, when related to the base current of the transistor in forward active mode, enables the prediction of optical characteristics. The importance of collection efficiency in accurate SR modelling is highlighted and the layer dependence of the optical flux absorption profile at near-band gap wavelengths is also investigated and its generalisation as a single-exponential has been refuted for GaAs-based HPTs. Analytical modelling of the spectral response has also been developed from the resolution of continuity equations that govern the excess optically generated minority carrier variation in the active layers of the HPT, taking into account the related physical parameters. Realistic boundary conditions have been considered for efficient device operation and a detailed optical flux absorption profile is constructed for accurate device modelling. This analytical model provides insight into the direct influence of various parameters (such as base width and carrier concentration) on the device performance, thus, providing a valuable optimization tool for the future design of HPTs in optical receivers. The measured results at 635 nm, 780 nm 808 nm and 850 nm for AlGaAs/GaAs HPTs and 980 nm, 1310 nm and 1550 nm for InP/InGaAs HPTs show good agreement with the predicted data, validating the proposed theoretical model. Finally, a detailed absorption model and photoresponse of double heterojunction phototransistors in a top/surface-illuminated orientation has been analyzed with a modified small-signal model. The effect of incident optical illumination on intrinsic small-signal parameters such as resistances and capacitances has been discussed and analyzed for photoresponse modelling.
2

Polychromatic determination of spectral response of PV devices

Sara, Ira D. January 2014 (has links)
This thesis introduces a novel spectral response (SR) measurement technique using polychromatic filters (filters with very broad spectral transmittances) to determine SR of large area PV devices. Conventionally, SR of a photovoltaic (PV) device is determined by illuminating the device under test (DUT) with a series of monochromatic beams at different wavelengths as described in the international standard IEC 60904-8, or beams of limited spectral content using narrow band pass filters or monochromator. One significant problem associated with the application of the narrow band pass filters for a large-area SR measurement is that low light intensity produced on the measurement plane particularly in certain wavelength ranges: the ultraviolet and infrared. This can produce weak signal responses from a tested PV device. In addition, the imperfection of the filter s mounting position can shift the peak wavelength of the filter s transmittance at angle of incidence greater than 10°. This can cause stray light on the measurement plane. The proposed SR measurement method is called the 'polychromatic SR fitting method' or, in short, it is known as the 'polychromatic method'. The advantage of this method is that higher beam intensity can be produced on the measurement plane as a result of large spectral transmittance of the polychromatic filters. This can improve the signal strength of a tested PV device. This new SR measurement method works by comparing the variations in the currents which are measured at different spectra to the currents which are calculated at the same spectral conditions using the SR model. Validations of this method for a large- and small-area SR determinations show that it is potentially feasible as a new technique for determining SR of a PV device with deviations within ±2% across the wavelength bands.
3

Numerical modeling of CdS/CdTe Thin Film Solar Cell using MEDICI

Muthuswamy, Gokul 26 October 2005 (has links)
Thin Film CdS/CdTe Solar cells have been an attrative alternative to silicon solar cells because of their low cost. Numerical Modeliong using using various tools pertinent only to solar cells have been employed to study the device properties. In this work a powerful device simulation tool MEDICI is used to develop a quantitative device model. The model is modified to accommodate a glass layer and an AM1.5 spectrum is used as the simlation of light source. Analysis of the response of solar cell J-V parameters like voc and Jsc to changes in acceptor concentration, CdTe thickness and changes in the work function of the back contact under intrinsic conditions were done. Trap levels were then added in the midgap regionof the device and the earlier variations were comprehensively studied to establish the trap parameters. Further this model was extended to perform the C-V analysis of the device. Finally two cases were analysed having their energy band profile as the baseline to fix their corresponding J-V responses. The anamolous behaviour of the J-V curves namely the rollover and crossover effects were noted in detail.
4

Optical response of polycrystalline mercuric iodide photoconductive detectors

Chegoor, Prashant 01 June 2005 (has links)
Mercuric Iodide in its tetragonal form has received a lot of attention for many years as a prospective room temperature X-ray and y-ray detector. Its basic properties are well suited for this purpose. Its wide band gap of 2.1eV contributes to a high dark resistivity of 1012ohm-cm or higher. A high atomic number of its constituent atoms (Hg-80, I -53) and a density of 6.3g/cm3 result in its efficient interaction with incident X-ray or y-ray radiation. Single crystalline mercuric iodide has been thoroughly studied and successfully utilized in commercial radiation detectors. But with the urgent need for large area ,low cost efficient X-ray detectors, focus has now shifted towards the development and understanding of the properties of thin film Polycrystalline Mercuric iodide detectors. Such detectors also have the advantage of being most suited for direct X-ray detection i.e. a direct conversion of incident X rays into electric signals which are then used to obtain an equivalent image in digital X-ray imaging. They also can be used in applications where a scintillator intermediate is used to generate visible light from incident high energy photons.Therefore it is important to study their optical response in order to understand and evaluate their Optical Properties. The present work focuses on obtaining the Optical response of the thin film Mercuric iodide photoconductive detectors .These films were grown on TEC-15 LOF glass with a Tin Oxide (SnO2) coating on it, which acts as a growth surface for the films and also functions as the front contact of the detector.Palladium which is sputtered on top of this film acts as the back contact. There are a total of seven contacted devices on each film sample and each device has been tested for its optical response in terms of Spectral Response and I-V characteristics in both light and dark conditions.
5

Ultrafast third-order nonlinearities in novel zwitterionic molecules

Smith, Euan Christopher January 1998 (has links)
No description available.
6

Design, Assembly And Calibration Of An Experimental Setup For Various Optical Measurements

Uzgel, Evren 01 January 2004 (has links) (PDF)
The experimental setup which consisted of the Jarrell-Ash Ebert type scanning monochromator, the Hamamatsu Si PIN Photodiode, a PC connected ADC card and a Tungstenstriplamp operated at different temperatures was assembled. The different parts needing calibration were calibrated with spectral response calibration techniques suitable for our purposes and connected to the experimental setup in a proper way. Spectral response calibrations and transmission measurements in the range 450-800 nm were carried out.
7

Modélisation spectrale de détecteurs matriciels infrarouge HgCdTe : application à un micro-spectromètre / Spectral modeling of HgCdTe infrared detector arrays : application to a micro-spectrometer

Mouzali, Salima 16 November 2015 (has links)
Face à l’émergence de l’imagerie multi et hyperspectrale, il existe une demande croissante de connaissance fine de la réponse spectrale des détecteurs infrarouge. Dans ce travail de thèse, nous proposons une démarche de modélisation optique des réponses spectrales des plans focaux infrarouge HgCdTe. L’objectif est de mieux maîtriser les origines physiques des oscillations observées sur les réponses spectrales des pixels d’une matrice de détection, ainsi que des disparités de longueurs d’onde de coupure. Ces phénomènes étaient peu étudiés dans la littérature; pourtant, ils sont responsables en partie du bruit spatial fixe qui limite les performances des détecteurs. Nous proposons une description qui conserve l’interprétation physique des phénomènes observés (absorption, interférences,…), tout en permettant d’extraire les paramètres technologiques (responsables de ces non-uniformités) de la façon la plus indépendante possible. Le principe repose sur la décomposition du comportement global du détecteur, qui peut sembler complexe, en une multitude de briques élémentaires, simples à modéliser. L’étude a été appliquée au cas particulier d’un micro-spectromètre infrarouge intégré au plan de détection. Une analyse de sensibilité sur le modèle proposé a alors permis d’évaluer la précision nécessaire sur les paramètres technologique afin d’obtenir une bonne qualité de restitution de spectres. Cette démarche est généralisable à d’autres architectures de détecteurs et d’autres technologies de fabrication, à condition de maîtriser les propriétés optiques des matériaux mis en jeu. / Due to the emergence of multi and hyperspectral imaging, there is an increasing demand for the control of the spectral response of infrared detectors. In this thesis, we propose an optical modelling approach of the spectral response of HgCdTe focal plane arrays. The aim is to better identify the physical origins of the oscillations observed on the spectral responses of the pixels belonging to the same detector array, as well as the cutoff wavelength disparities. These phenomena were not studied in the literature; though, they are partly responsible for the fixed pattern noise that limits the performance of the detectors. We propose a description that takes account of the physical interpretation of the observed phenomena (absorption, interference…), while allowing the extraction of the technological parameters (that are responsible for such non-uniformities) in the most independent way possible. The principle is based on the decomposition of the global behaviour of the detector, which may seem complex, as a multitude of elementary phenomena, which are easy to model. The study was applied to the particular case of a micro-spectrometer integrated to an infrared detection array. A sensitivity analysis of the proposed model was then performed to deduce the necessary precision on the technological parameters to obtain good quality spectra restitution. This approach can be generalized to other architectures detectors and other manufacturing technologies, provided that the optical properties of the materials involved are well known.
8

Relação entre parâmetros de qualidade de água e dados do sensor OLI, Landsat 8, no Guaíba, Rio Grande do Sul, Brasil

Tebaldi, Charles January 2015 (has links)
A bacia hidrográfica do Guaíba possui uma área de 2.253 km² e apresenta uma população de mais de um milhão de habitantes, a grande maioria concentrada na região metropolitana de Porto Alegre. Estudos apontam um elevado nível de poluição nas suas águas, deixando-as longe das condições sanitárias adequadas. A utilização de técnicas de sensoriamento remoto para o gerenciamento de rios e lagoas se baseia no fato de que a descarga de sedimentos, a eutrofização e o aumento na produtividade de algas estão associadas às mudanças nas propriedades ópticas da camada superficial do corpo de água. O objeto deste trabalho é a análise das variáveis limnológicas das águas do Lago Guaíba - transparência, concentração de sedimentos em suspensão (CSS) e concentração de material orgânico (CMO) – no dia 20 de dezembro de 2013 e a relação entre elas e a resposta espectral nas bandas do visível (0,45 a 0,67 m), do sensor OLI - Landsat 8, naquela e em mais 6 datas durante o ano de 2014 em um transecto do Lago. Realizou-se a análise de correlação entre as variáveis limnológicas e os dados de reflectância. Observou-se uma relação inversamente proporcional entre transparência e CSS. Estatisticamente, a correlação (-0,605) se mostrou com nível de confiança de 0,05 entre a banda 2 (0.45 e 0.51m), do sensor OLI e a transparência da água. Para CSS também se verificou uma correlação ao nível de significância de 0,01 com a transparência da água, gerando um coeficiente de regressão (R²) 0,87 entre eles. A transparência apresentou correlação (-0,644) com CMO ao nível de significância de 0,05. Encontrou-se uma relação baixa (0,443) entre CSS e a banda 2, significante a 95%. As demais correlações das bandas do visível com CSS e CMO os resultados não foram significativos. Os resultados permitiram espacializar a distribuição espacial da transparência, CSS e CMO da água, através de mapas e, com isso, caracterizar o Guaíba de maneira satisfatória para o dia 20 de dezembro de 2013. A análise considerando apenas um transecto monitorado apresentou resultados satisfatórios apenas para as relações: “transparência e banda 2” e “CSS e banda 2”. A baixa correlação com as demais bandas do espectro do visível do sensor OLI – Landsat 8 e os dados limnológicos mostram como é complexo trabalhar com dados de sensoriamento remoto utilizando sensor multiespectral em um corpo d’água natural como o Guaíba. / The Guaíba watershed has an area of 2,253 km ² and has a population of over one million population, mostly concentrated in the metropolitan region of Porto Alegre. Studies indicate a high level of pollution in its waters, leaving them far from adequate sanitary conditions. The use of remote sensing techniques for the management of rivers and Lakes is based on the fact that the discharge of sediments, eutrophication and the increase in productivity of algae are associated to changes in optical properties of the surface layer of the water body. The objective of this work is the analysis of limnological variables in the waters of Lake Guaiba - transparency, concentration of suspended sediment (CSS) and concentration of organic material (CMO) - on December 20, 2013 and the relation between them and the spectral response bands in the visible bands (0.45 to 0.67 m), the OLI sensor - Landsat 8, and more 6 dates between 2014 in a transect of the Lake. There was the analysis of correlation between the variables limnological and reflectance data. There was an inverse relation between transparency and CSS. Statistically, the correlation (-0.605) proved with 0.05 level trusty between the band 2 (0.45 and 0.51m), the OLI sensor and water transparency. The CSS also has been a correlation to the 0.01 significance level to the transparency of the water, beget a regression coefficient (R²) 0.87 between them. Transparency correlated (-0.644) with CMO at the 0.05 significance gap. A low proportion (0.443) between CSS and the band 2, significant at 95% was found. The other correlations of the visible bands and CSS and CMO and the results were not significant. Results allowed spacialized distribution transparency, CSS and CMO of water, through maps and thereby characterize the Guaiba Lake on December 20, 2013. The analysis considering one transect monitored show satisfactory just a results for relationship: "transparency and band 2" and "CSS and Band 2". Low correlation with other visible spectrum bands of the visible sensor OLI - Landsat 8 and limnology data show how complex work with remote sensing data using multispectral sensor in a natural body of water as the Guaiba Lake.
9

Relação entre parâmetros de qualidade de água e dados do sensor OLI, Landsat 8, no Guaíba, Rio Grande do Sul, Brasil

Tebaldi, Charles January 2015 (has links)
A bacia hidrográfica do Guaíba possui uma área de 2.253 km² e apresenta uma população de mais de um milhão de habitantes, a grande maioria concentrada na região metropolitana de Porto Alegre. Estudos apontam um elevado nível de poluição nas suas águas, deixando-as longe das condições sanitárias adequadas. A utilização de técnicas de sensoriamento remoto para o gerenciamento de rios e lagoas se baseia no fato de que a descarga de sedimentos, a eutrofização e o aumento na produtividade de algas estão associadas às mudanças nas propriedades ópticas da camada superficial do corpo de água. O objeto deste trabalho é a análise das variáveis limnológicas das águas do Lago Guaíba - transparência, concentração de sedimentos em suspensão (CSS) e concentração de material orgânico (CMO) – no dia 20 de dezembro de 2013 e a relação entre elas e a resposta espectral nas bandas do visível (0,45 a 0,67 m), do sensor OLI - Landsat 8, naquela e em mais 6 datas durante o ano de 2014 em um transecto do Lago. Realizou-se a análise de correlação entre as variáveis limnológicas e os dados de reflectância. Observou-se uma relação inversamente proporcional entre transparência e CSS. Estatisticamente, a correlação (-0,605) se mostrou com nível de confiança de 0,05 entre a banda 2 (0.45 e 0.51m), do sensor OLI e a transparência da água. Para CSS também se verificou uma correlação ao nível de significância de 0,01 com a transparência da água, gerando um coeficiente de regressão (R²) 0,87 entre eles. A transparência apresentou correlação (-0,644) com CMO ao nível de significância de 0,05. Encontrou-se uma relação baixa (0,443) entre CSS e a banda 2, significante a 95%. As demais correlações das bandas do visível com CSS e CMO os resultados não foram significativos. Os resultados permitiram espacializar a distribuição espacial da transparência, CSS e CMO da água, através de mapas e, com isso, caracterizar o Guaíba de maneira satisfatória para o dia 20 de dezembro de 2013. A análise considerando apenas um transecto monitorado apresentou resultados satisfatórios apenas para as relações: “transparência e banda 2” e “CSS e banda 2”. A baixa correlação com as demais bandas do espectro do visível do sensor OLI – Landsat 8 e os dados limnológicos mostram como é complexo trabalhar com dados de sensoriamento remoto utilizando sensor multiespectral em um corpo d’água natural como o Guaíba. / The Guaíba watershed has an area of 2,253 km ² and has a population of over one million population, mostly concentrated in the metropolitan region of Porto Alegre. Studies indicate a high level of pollution in its waters, leaving them far from adequate sanitary conditions. The use of remote sensing techniques for the management of rivers and Lakes is based on the fact that the discharge of sediments, eutrophication and the increase in productivity of algae are associated to changes in optical properties of the surface layer of the water body. The objective of this work is the analysis of limnological variables in the waters of Lake Guaiba - transparency, concentration of suspended sediment (CSS) and concentration of organic material (CMO) - on December 20, 2013 and the relation between them and the spectral response bands in the visible bands (0.45 to 0.67 m), the OLI sensor - Landsat 8, and more 6 dates between 2014 in a transect of the Lake. There was the analysis of correlation between the variables limnological and reflectance data. There was an inverse relation between transparency and CSS. Statistically, the correlation (-0.605) proved with 0.05 level trusty between the band 2 (0.45 and 0.51m), the OLI sensor and water transparency. The CSS also has been a correlation to the 0.01 significance level to the transparency of the water, beget a regression coefficient (R²) 0.87 between them. Transparency correlated (-0.644) with CMO at the 0.05 significance gap. A low proportion (0.443) between CSS and the band 2, significant at 95% was found. The other correlations of the visible bands and CSS and CMO and the results were not significant. Results allowed spacialized distribution transparency, CSS and CMO of water, through maps and thereby characterize the Guaiba Lake on December 20, 2013. The analysis considering one transect monitored show satisfactory just a results for relationship: "transparency and band 2" and "CSS and Band 2". Low correlation with other visible spectrum bands of the visible sensor OLI - Landsat 8 and limnology data show how complex work with remote sensing data using multispectral sensor in a natural body of water as the Guaiba Lake.
10

Relação entre parâmetros de qualidade de água e dados do sensor OLI, Landsat 8, no Guaíba, Rio Grande do Sul, Brasil

Tebaldi, Charles January 2015 (has links)
A bacia hidrográfica do Guaíba possui uma área de 2.253 km² e apresenta uma população de mais de um milhão de habitantes, a grande maioria concentrada na região metropolitana de Porto Alegre. Estudos apontam um elevado nível de poluição nas suas águas, deixando-as longe das condições sanitárias adequadas. A utilização de técnicas de sensoriamento remoto para o gerenciamento de rios e lagoas se baseia no fato de que a descarga de sedimentos, a eutrofização e o aumento na produtividade de algas estão associadas às mudanças nas propriedades ópticas da camada superficial do corpo de água. O objeto deste trabalho é a análise das variáveis limnológicas das águas do Lago Guaíba - transparência, concentração de sedimentos em suspensão (CSS) e concentração de material orgânico (CMO) – no dia 20 de dezembro de 2013 e a relação entre elas e a resposta espectral nas bandas do visível (0,45 a 0,67 m), do sensor OLI - Landsat 8, naquela e em mais 6 datas durante o ano de 2014 em um transecto do Lago. Realizou-se a análise de correlação entre as variáveis limnológicas e os dados de reflectância. Observou-se uma relação inversamente proporcional entre transparência e CSS. Estatisticamente, a correlação (-0,605) se mostrou com nível de confiança de 0,05 entre a banda 2 (0.45 e 0.51m), do sensor OLI e a transparência da água. Para CSS também se verificou uma correlação ao nível de significância de 0,01 com a transparência da água, gerando um coeficiente de regressão (R²) 0,87 entre eles. A transparência apresentou correlação (-0,644) com CMO ao nível de significância de 0,05. Encontrou-se uma relação baixa (0,443) entre CSS e a banda 2, significante a 95%. As demais correlações das bandas do visível com CSS e CMO os resultados não foram significativos. Os resultados permitiram espacializar a distribuição espacial da transparência, CSS e CMO da água, através de mapas e, com isso, caracterizar o Guaíba de maneira satisfatória para o dia 20 de dezembro de 2013. A análise considerando apenas um transecto monitorado apresentou resultados satisfatórios apenas para as relações: “transparência e banda 2” e “CSS e banda 2”. A baixa correlação com as demais bandas do espectro do visível do sensor OLI – Landsat 8 e os dados limnológicos mostram como é complexo trabalhar com dados de sensoriamento remoto utilizando sensor multiespectral em um corpo d’água natural como o Guaíba. / The Guaíba watershed has an area of 2,253 km ² and has a population of over one million population, mostly concentrated in the metropolitan region of Porto Alegre. Studies indicate a high level of pollution in its waters, leaving them far from adequate sanitary conditions. The use of remote sensing techniques for the management of rivers and Lakes is based on the fact that the discharge of sediments, eutrophication and the increase in productivity of algae are associated to changes in optical properties of the surface layer of the water body. The objective of this work is the analysis of limnological variables in the waters of Lake Guaiba - transparency, concentration of suspended sediment (CSS) and concentration of organic material (CMO) - on December 20, 2013 and the relation between them and the spectral response bands in the visible bands (0.45 to 0.67 m), the OLI sensor - Landsat 8, and more 6 dates between 2014 in a transect of the Lake. There was the analysis of correlation between the variables limnological and reflectance data. There was an inverse relation between transparency and CSS. Statistically, the correlation (-0.605) proved with 0.05 level trusty between the band 2 (0.45 and 0.51m), the OLI sensor and water transparency. The CSS also has been a correlation to the 0.01 significance level to the transparency of the water, beget a regression coefficient (R²) 0.87 between them. Transparency correlated (-0.644) with CMO at the 0.05 significance gap. A low proportion (0.443) between CSS and the band 2, significant at 95% was found. The other correlations of the visible bands and CSS and CMO and the results were not significant. Results allowed spacialized distribution transparency, CSS and CMO of water, through maps and thereby characterize the Guaiba Lake on December 20, 2013. The analysis considering one transect monitored show satisfactory just a results for relationship: "transparency and band 2" and "CSS and Band 2". Low correlation with other visible spectrum bands of the visible sensor OLI - Landsat 8 and limnology data show how complex work with remote sensing data using multispectral sensor in a natural body of water as the Guaiba Lake.

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