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1
Kumar, Nikhil P. "Light beam propagation in complex crystals." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/405772.
Full textAbstract:
Recent advancement in Photonics have brought about a new era of miniaturisation. Along came a need for technology to allow the manipulation of light at the micrometer scale, with precise control over beam propagation. The past decades have seen numerous studies devoted to periodic nanophotonic structures, Photonic Crystals (PhCs), which brought out different temporal and spatial functionalities such as frequency bandgaps, waveguiding, or managing diffractive properties of the beam. More recently, attention was paid to equally accessible artificial nanophotonic structures, where gain and losses are modulated on the wavelength scale: Gain Loss Modulated Materials (GLMMs). Therefore, the aim of my PhD was providing a deep analysis on beam propagation in GLMMs, identifying the spatial propagation effects they held and proposing realistic scenarios in which they could be implemented, in existing and evolving technology and devices. We built our studies from a solid understanding of GLMMs of prior works performed, however, using a paraxial approximation, which reduces the predictions accuracy by excluding propagation at large angles. The methodology adopted is a combination of analytical predictions and numerical confirmation of the predicted effects. We initially investigated the high anisotropy of beam amplification/attenuation within GLMMs. As predicted by the plane wave expansion method, the propagation of light beams within such structures is sensitive to the propagation direction. We provided a numerical proof in 2D periodic Loss Modulated Materials (LMM) with square and rhombic lattice symmetry, by solving the full set of Maxwell¿s equations, using the finite difference time domain method, which entails no approximation. Anisotropy of amplification/attenuation leads to the narrowing of the angular spectrum of beams with wavevectors close to the edges of the first Brillouin Zone. The effect provides a novel tool to filter out high spatial harmonics from noisy beams, while being amplified. A later study lead us to analyse the focalisation performance of a flat LMM slab. Flat lensing was analytically predicted by the dispersion curves obtained from a coupled mode expansion of Maxwell¿s equations, and then numerically confirmed. For a range of frequencies coinciding with a high transmission window at resonant Bragg frequencies (bandgap frequencies for PhCs), light beams undergo negative (anomalous) diffraction through LMMs. The phase shifts accumulated within the structure are then compensated by normal diffraction in free space, leading to a substantial focalization beyond it. The predicted phenomena are generic for spatially modulated materials and other kinds of waves. Thus, we also discussed, for the first time, propagation in LMM acoustic crystals, predicting high angular transmission bands. While these initial studies assumed hypothetical LMM materials, in a realistic scenario, loss modulations are always accompanied by refractive index modulations, as predicted by Kramers-Kronig relations. During the final phase of my PhD, we focused on more realistic structures exhibiting both index and loss modulations, namely metallic photonic crystals (MPhCs), made of 2D rhombic arrays of metallic cylinders embedded in air. We explored their ability to tailor the spatial propagation of light beams. Indeed, MPhCs support self-collimated propagation and negative diffraction. In this later case, flat lensing was demonstrated, leading to the focalization of beams behind MPhCs slabs. Also, the anisotropic attenuation of light within MPhCs enables spatial filtering. Finally, we initiated studies towards the implementation of GLMMs as an intrinsic mechanism to improve the beam quality from Broad Area Semiconductor (BAS) amplifiers. Along the development of my PhD, we proposed, analysed and established spatial beam propagation effects in GLMM, from purely ideal LMM structures to more realistic structure as MPhCs or BAS amplifiers.Els avenços recents en Fotònica han començat una nova era de miniaturització, apareixent la necessitat tecnològica de manipular la llum a l'escala micromètrica, amb un control precís de la propagació del feixos. Les darreres dècades han estat testimoni de nombrosos estudis dedicats a estructures periòdiques nanofotòniques, Cristalls Fotònics (PhC), amb propietats temporals i espacials, com ara bandes prohibides de freqüència, guies d'ones, o el control sobre la difracció dels feixos de llum. Més recentment, s'han considerat altres estructures artificials nanofotòniques igualment accessibles, amb guanys i pèrdues modulades a l'escala de la longitud d'ona, Materials Modulats amb Guanys i Pèrdues (GLMMs). Així, l'objectiu de la meva tesi doctoral és proporcionar una anàlisi profunda sobre la propagació dels feixos de llum en GLMMs, identificant efectes espacials i proposant escenaris reals per implementar-los, en tecnologies i dispositius ja existents o en desenvolupament. Els treball parteix d'estudis previs que proporcionen una comprensió sòlida dels GLMMs, malgrat que es basen en l'aproximació paraxial, reduint la precisió de les prediccions ja que s'exclou la propagació a angles grans. La metodologia adoptada és una combinació de prediccions analítiques i confirmació numèrica dels efectes predits. Inicialment, s'investiga l'alta anisotropia d'amplificació/atenuació de feixos dins GLMMs. Tal com es prediu amb el mètode d'expansió en ones planes, la propagació del feixos en aquestes estructures és molt sensible a la direcció; proporcionant la prova numèrica en Materials 2D amb Pèrdues Modulades (LMM) amb simetria de xarxa quadrada i romboïdal, resolent el conjunt complet de les equacions de Maxwell (mètode de diferències finites en domini temporal), sense cap aproximació. L'anisotropia de l'amplificació/atenuació redueix l'espectre angular dels feixos amb vectors d'ona propers als límits de la primera zona de Brillouin; efecte que proporciona una nova eina per filtrar harmònics espacials de feixos amb soroll, mentre s'amplifiquen. Un estudi posterior duu a analitzar la possibilitat de focalitzar amb una làmina plana LMM. L'efecte es prediu analíticament amb les corbes de dispersió (expansió en modes acoblats de les equacions de Maxwell) i es confirma numèricament. Per a un rang de freqüències dins la finestra d'alta transmissió de les freqüències ressonants de Bragg (banda prohibida per a PhC), la difracció és negativa (anòmala) a través de l'LMM. La difracció normal de l'espai lliure compensa la fase negativa acumulada en l'estructura i el feix focalitza després de la làmina. Els fenòmens predits són genèrics pels materials modulats espacialment i altres tipus d'ones. També s'estudia, per primera vegada, la propagació en cristalls acústics LMM, predient bandes angulars d'alta transmissió. Malgrat inicialment es consideren materials LMM ideals, en un escenari més realista, les modulacions de pèrdues van sempre acompanyades de modulacions d'índex de refracció segons les relacions de Kramers-Kronig. La fase final de la meva Tesi se centra en estructures més realistes tant amb modulacions d'índex com de pèrdues: cristalls fotònics metàl·lics (MPhCs), formats per distribucions periòdiques ròmbiques de cilindres metàl·lics en aire, explorant-ne la capacitat per controlar la propagació de feixos de llum. En MPhCs és possible tant la propagació col·limada com la difracció negativa. En aquest últim cas, es demostra la focalització per làmines planes de MPhCs. A més, l'atenuació anisòtropa de la llum permet el filtratge espacial. Finalment, s'explora l'aplicació dels GLMMs com a mecanisme intrínsec per millorar la qualitat dels feixos emesos per amplificadors de semiconductors (BAS). Al llarg de la meva tesi doctoral, s’han proposat, analitzat i establert mecanismes de control de la difracció de feixos de llum en GLMM, des d'estructures purament ideals LMM a més realistes com MPhCs o amplificadors BAS.
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Maigyte, Lina. "Shaping of light beams with photonic crystals : spatial filtering, beam collimation and focusing." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/277571.
Full textAbstract:
The research developed in the framework of this PhD thesis is a theoretical, numerical and experimental study of light beam shaping (spatial filtering, beam collimation and focusing) in the visible frequency range using photonic crystal structures. Photonic crystals (PhCs) are materials with periodic, spatially modulated refractive index on the wavelength scale. They are primarily known for their chromatic dispersion properties. However, they can also modify the spatial dispersion, which allows managing the spatial properties of the monochromatic light beams.
In the first part of my thesis we experimentally show that particular spatial dispersion modification in PhCs can lead to spatial (angular) filtering of light beams. The study is focused on the spatial filtering efficiency improvement by introducing chirp (the variation of longitudinal period of the structure) in the crystal structure. Additionally, to enhance the effect, we consider different geometries and materials. The work presented in this PhD thesis brings closer to reality the creation of a new generation spatial filters for micro-photonic circuits and micro-devices.
The second part of the study is devoted to the theoretical, numerical and experimental analysis of the formation of negative spatial dispersion in PhCs, which gives rise to collimation and focusing effects behind the PhCs. The ideas developed in my PhD also work in lossy systems, in particular in metallic PhCs. The simulation results for metallic PhCs are presented, in which both effects- spatial filtering and beam focusing, are shown.La recerca desenvolupada en el marc d'aquesta tesi doctoral és un estudi teòric, numèric i experimental de la modificació de la forma de feixos de llum (filtratge espacial, col·limació i focalització) en el rang visible de freqüències utilitzant estructures de cristall fotònic. Els cristalls fotònics (CFs) són materials amb una modulació periòdica de l'índex de refracció en l'escala de la longitud d'ona, i són principalment coneguts per les seves propietats relacionades amb la dispersió temporal. Tot i això, la dispersió espacial també pot ser modificada mitjançant CFs, fet que permet controlar les propietats espacials de feixos monocromàtics de llum. En la primera part de la tesi, mostrem experimentalment el fet que certes modificacions de la dispersió espacial en CFs poden donar lloc a filtratge espacial (angular) de feixos de llum. L'estudi es focalitza en la millora de l'eficiència del filtratge espacial mitjançant la introducció de "chirp" (la variació del període longitudinal de l'estructura) en el CF. A més, per tal d'incrementar l'efecte considerem diferents estructures i materials. El treball presentat en aquesta tesi doctoral acosta a la realitat la creació d'una nova generació de filtres espacials per a circuits micro-fotònics i micro-dispositius. La segona part d'aquest estudi se centra en l'anàlisi teòric, numèric i experimental de la formació de dispersió espacial negativa en CFs, la gual dóna lloc a efectes de col·limació i focalització un cop travessat el CF. Les idees desenvolupades en aquesta tesi doctoral també són aplicables a sistemes amb pèrdues, en particular a CFs metàl·lics. Els resultats de les simulacions mostren l'existència d'ambdós efectes, filtratge espacial i focalització, en CFs metàl·lics.
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Horger, John. "Multiple plane wave analysis of acousto-optic diffraction of Gaussian shaped light beams." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/44053.
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A short history of acousto-optics research is presented
along with a general description of how light and sound
interact.
The Multiple Scattering model is derived and used with a Gaussian light beam to observe the distortion in light beam profile within the sound field. Numerical results are presented for comparison to previous studies using thick holograms and two orders of light. The results from using two light orders are compared to four light order results.
A Hamming sound amplitude distribution is introduced as
a possible way to reduce the amount of light beam profile
distortion.
Master of Science
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Wilson, Rebecca Anne. "The electron-beam tunable interference filter spatial light modulator." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/1494.
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Bryan, Charles Edward. "An electron beam addressed liquid crystal light valve projector." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235841.
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The contents of this dissertation relate to a liquid crystal light valve which is addressed by an electron beam. The light valve has been configured with a computer aided designed optical projection system, to produce an electron beam addressed liquid crystal light valve projector. The projector is capable of turning an electrical signal into a corresponding projected picture. A minimum resolution of 33um was demonstrated in a smectic-A liquid crystal light valve and one of 40um in a dyed phase change guest-host liquid crystal light valve. The diameter of the active area of the light valve was 45mm. Crucial to the realization of the projector was the patented invention and design of an electrically highly anisotropic disc of 47mm diameter which was approximately 2mm thick. The disc, which was conducting through its thickness and insulating across its plane, formed the top interface of the liquid crystal light valve and permitted the electron beam to deposit a charge pattern which could be conveyed to the thin liquid crystal layer without loss of resolution. The disc was made using a specially constructed piece of apparatus wherein the holes in a glass capillary array were filled with a low melting point alloy. Discs were made using three different low melting point alloys and their various merits were considered. Consideration was also given to developing the deflection coils used in this projector. Computer aided design resulted in a deflection coil system capable of a resolution of over 8 x 108 pixels in a 50mm x 50mm frame at a half angular aperture of 1mrad. In order to evaluate the resolution of the light valve, a micro-computer controlled dot pattern generator was built. This was used to drive the deflection coils in such a way as to control both the dwell time and position of the electron beam spot. Lines of different spacings were written on the light valve. Electron and optical micrographs are presented to demonstrate the quality of the anisotropic disc. Photographs and optical micrographs are included to show the pictures which were obtained from the projector and also the lines written on the light valve.
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Liu, Lihong. "Beam shaping of incoherent white light with faceted structure." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD010.
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La mise en forme de lumière blanche incohérente à l’aide d’un nouveau composant est proposée dans cette thèse. L'objectif était de réaliser une carte d'irradiance arbitraire sur un écran à l’aide d’une structure originale contenant seulement des facettes, légèrement inclinées par rapport à la direction d'origine selon leurs axes propres. Une approche basée sur l’optique géométrique a été utilisée pour concevoir et analyser la structure proposée. Celle-ci est constituée d’une matrice de facettes jouant le rôle de déflecteur. Nous avons étudié le cas en transmission et en réflexion. L’obtention des angles d’inclinaison s’est faite avec deux approches différentes : l'optimisation sous Zemax et le calcul analytique. Plusieurs critères de qualité ont été proposés pour comparer la carte d'irradiance. Le tolérancement a démontré qu’il est plus intéressant de travailler en transmission qu’en réflexion. Une réalisation a été faite avec succès en utilisant une technologie additive innovanteBeam shaping of incoherent white light with a large spectrum is proposed in this PhD thesis. The objective was to realize an arbitrary irradiance map on a target plane using a faceted structure. To maintain the design result within the geometrical optics domain, large facet element dimensions are required to obtain usable results. Each facet element can slightly tilt along its own axes to deflect the incident light, either by reflection, either by transmission. The calculation of the tilt angles is made by an analytical approach, and also by automatic optimization with Zemax. Several quality factors are proposed in order to qualify the illumination/irradiance chart on the screen. Because of the required tolerances on the fabrication technique, we show that it is more interesting to design a transmissive structure than a reflective one. With a new additive technology, a structure is realized successfully, showing the interest of the concept
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Hällstig, Emil. "Nematic Liquid Crystal Spatial Light Modulators for Laser Beam Steering." Doctoral thesis, Uppsala University, Quantum Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4693.
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Laser beam control is important in many applications. Phase modulating spatial light modulators (SLMs) can be used to electronically alter the phase distribution of an optical wave-front and thus change the direction and shape of a laser beam. Physical constraints set limitations to the SLM and an ideal phase distribution can usually not be realised. In order to understand how such components can be used for non-mechanical beam control three nematic liquid crystal (NLC) SLMs have been thoroughly characterised and modelled.
The pixel structure and phase quantisation give a discrepancy between ideal and realised phase distributions. The impact on beam steering capability was examined by measurements and simulations of the intensity distribution in the far-field.
In two of the studied SLMs the pixel period was shorter than the thickness of the LC layer giving the optical phase shift. This results in a so-called “fringing field”, which was shown to degrade the phase modulation and couple light between polarisation modes. The deformation of the LC was simulated and a finite-difference time-domain (FDTD) algorithm was used to calculate how polarised light propagates through the optically anisotropic SLM.
Non-mechanical beam steering and tracking in an optical free-space communication link were demonstrated. Continual optimisation of the steering angle was achieved by feedback from a video camera.
The optical properties of the SLM in the time period right after a voltage update were studied. It was shown how light is redistributed between orders during the switching from one blazed grating to another. By appropriate choice of the blazed gratings the effects on the diffraction efficiency can be minimised.
The detailed knowledge of the SLM structure and its response to electronic control makes it possible to predict and optimise the device performance in future systems.
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Hällstig, Emil. "Nematic liquid crystal spatial light modulators for laser beam steering /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4693.
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Rhodes, Daniel Paul. "Experimental studies of cold atom guiding using hollow light beams." Thesis, University of St Andrews, 2005. http://hdl.handle.net/10023/12932.
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This thesis is concerned with the guiding of cold atoms using optical forces, which is of great importance in the field of atom optics. Atomic beams can be used for precision sensor equipment, building nano-scale structures, construction of quantum computers and to further the understanding of the properties of atoms. Atoms are guided along light beams using the dipole force; there are two regimes under which this force works. Typically red-detuned guides are used (atoms are attracted towards the light) such guides, however, require large detuning and high powers. In this thesis we investigate the use of blue-detuned (atoms are repelled from the light) hollow light beams of moderate power (a few hundred mW) and confine atoms in the dark centre of the beams. Several magneto-optical traps (MOTs) have been constructed to exploit different guiding geometries. Hollow beams have been generated using a variety of methods; in particular the use of a computer controlled spatial light modulator (SLM) has provided great versatility and simplicity to the experimental arrangements. First, experiments were performed with a low-velocity intense source (LVIS) of atoms. A co-linear LG beam significantly enhances the observed flux, however, considerable difficulties are encountered loading atoms into oblique guides. Imaging a hole in the walls of the light tube was used to improve the loading efficiency. Second, guiding a free-falling atom cloud is performed using a non-diffracting Bessel beam. It is found that while the potential of the Bessel beam is steeper than equivalent LG beams the power distribution across the beam severely limits its usefulness. The next study investigated higher-order LG guide beams generated with an SLM. High order modes have a narrower profile so confine the atoms with less interaction with the guide beam, leading to a more natural guide (as opposed to a pushing force). Finally the SLM was used to create non-trivial beam shapes for beam splitters and interferometers.
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Hon, Hock-Woon. "The modelling of multiple beam x-ray systems using visible light." Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341275.
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Dimaria, Jeffrey V. "Plasmonic control of light emission for enhanced efficiency and beam shaping." Thesis, Boston University, 2014. https://hdl.handle.net/2144/10981.
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Thesis (Ph.D.)--Boston UniversityInGaN alloys and related quantum structures are of great technological importance for the development of visible light emitting devices, motivated by a wide range of applications, particularly solid-state lighting. The InxGa1-xN material system provides continuous emission tuning from the ultraviolet across the visible spectrum by changing the In content. InGaN/GaN quantum wells (QW) also provide an efficient medium for electroluminescence for use as light emitting diodes. It is well known, however, that increasing the In content degrades the internal quantum efficiency of these devices, particularly in the green region of the spectrum. These limitations must be overcome before efficient all-solid-state lighting can be developed beyond the blue-green region using this material system. Recently, the application of plasmonic excitations supported by metallic nanostructures has emerged as a promising approach to address this issue. In this work, metallic nanoparticles (NPs) and nanostructures that support plasmonic modes are engineered to increase the local density of states of the electromagnetic field that overlaps the QW region. This leads to an enhancement of the spontaneous emission rate of the QW region mediated by direct coupling into the plasmonic modes of the nanostructure. Energy stored in these modes can then scatter efficiently into free-space radiation, thereby enhancing the light output intensity. The first section of this thesis concerns the enhancement of InGaN/GaN QW light emission by utilizing localized surface plasmon resonances (LSPRs) and lattice surface modes of metal NP arrays. This work comprises a detailed study of the effect of geometry variations of Ag NPs on the LSPR wavelength, and the subsequent demonstration of photoluminescence intensity enhancement by Ag NPs in the vicinity of InGaN multiple QWs. The second section of this thesis concerns the far-field control of QW emission utilizing metallic nanostructures that support plasmonic excitations. This includes a study of the dispersion and competing effects of a metallic NP-film system, and the demonstration of beam collimation and unidirectional diffraction utilizing a similar geometry. These results may find novel applications in the emerging field of solid-state smart lighting.
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Nylk, Jonathan. "Advanced light-sheet and structured illumination microscopy techniques for neuroscience and disease diagnosis." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/10842.
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Optical microscopy is a cornerstone of biomedical research. Advances in optical techniques enable specific, high resolution, sterile, and biologically compatible imaging. In particular, beam shaping has been used to tailor microscopy techniques to enhance microscope performance. The aim of this Thesis is to investigate the use of novel beam shaping techniques in emerging optical microscopy methods, and to apply these methods in biomedicine. To overcome the challenges associated with high resolution imaging of large specimens, the use of Airy beams and related techniques are applied to light-sheet microscopy. This approach increases the field-of-view that can be imaged at high resolution by over an order of magnitude compared to standard Gaussian beam based light-sheet microscopy, has reduced phototoxicity, and can be implemented with a low-cost optical system. Advanced implementations show promise for imaging at depth within turbid tissue, in particular for neuroscience. Super-resolution microscopy techniques enhance the spatial resolution of optical methods. Structured illumination microscopy is investigated as an alternative for electron microscopy in disease diagnosis, capable of visualising pathologically relevant features of kidney disease. Separately, compact optical manipulation methods are developed with the aim of adding functionality to super-resolution techniques.
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Li, J. "Advanced laser beam shaping using spatial light modulators for material surface processing." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3022554/.
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Beam shaping is the process of redistributing the irradiance and phase of a beam of optical radiation. The beam shape is defined by the irradiance distribution. In recent years, laser beam shaping has been employed in many fields of scientific, engineering and industrial R&D for many applications, such as material processing, medical applications, lithography, optical data storage and laboratory research. In this thesis, a novel beam shaping technique is presented. Different from geometrical optics and diffractive methods, an imaging-based beam shaping system was built and tested. A laser beam was shaped using geometric masks applied on a spatial light modulator (SLM) at objective plane of a lens system and reconstructed at imaging plane. Geometric masks generated based on real beam profile can modulate both the outline profile and intensity distribution of the input laser. Laser parallel processing technique was also employed in this research to increase the beam shaping efficiency. The results obtained in this thesis demonstrate high accuracy and flexibility of this beam shaping technique, showing many potential applications.
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Kwarikunda, Nicholas. "On the characterisation of solar cells using light beam induced current measurements." Thesis, Nelson Mandela Metropolitan University, 2015. http://hdl.handle.net/10948/11147.
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The presence of inhomogeneities in semiconductor materials used to fabricate solar cell devices may result in spatial non uniformities in the device properties which may affect current generation in these devices. Besides, current reducing defects such as inclusions, local shunts and optical blockages may be introduced during the various device manufacturing processes which may adversely affect the performance and overall efficiency of solar cells. Diagnostic techniques are therefore needed to identify these defects so as to improve the production technology. This thesis presents the Light Beam Induced Current (LBIC) technique for mapping spatial non uniformities in solar cell devices. The LBIC is a non destructive characterisation technique that uses a focused light beam to raster scan a solar cell surface as the photo-generated current is recorded as a function of position to generate a photo-response map. The technique was used to obtain photoresponse maps for a mc-Si, Back contact Back junction (BC-BJ) silicon solar cell and the InGaP/InGaAs/Ge concentrating triple junction (CTJ) solar cell from which various local current reducing defects were mapped. A reflection signal detector was incorporated into the LBIC measurement system to enable us distinguish between optical blockages on the cell surface and current reducing defects within the solar cell devices. By dynamically biasing the solar cell devices, the electrical activity of the identified defects was investigated and also point-by-point current-voltage (I-V) characteristics were obtained. An interval division algorithm was applied to the measured point-by-point I-V characteristics to extract device and performance parameters from which device and performance parameter uniformity of the devices were mapped. Dark and full cell solar illumination I-V characteristics were also measured to extract device parameters. Analysis of extracted parameters revealed differences between extracted dark and illuminated device parameters which was attributed to departure from the superposition principle due to non-linearity of the semiconductor device equations with respect to carrier concentration. An investigation into the effect of illumination intensity on the I-V parameters of a spot illuminated BC-BJ Si solar cell showed a linear increase and a logarithmic increase of the short circuit current and open circuit voltage respectively with intensity while the series resistance decreased with intensity, which was attributed to increase in conductivity of the active layer. The ideality factor and saturation current were observed to increase while the shunt resistance initially increased before decreasing at higher intensity levels. Under monochromatic illumination, the photo-response of the BC-BJ Si cell was higher at 785nm than at 445nm due to low absorption coefficient of Si for longer wavelength radiations, resulting in carrier generation within the bulk, where there is a higher probability of carriers being collected at the p-n junction before they recombine. Under solar illumination, as the spectral content was altered using long pass colour filters with cut off wavelengths of 610nm and 1000nm, the performance parameters were observed to decrease and this was mainly due to decrease in intensity. For the CTJ solar cell, however, blocking of radiations below 610nm resulted in current mismatch that severely degraded the short circuit current (Isc). The current mismatch affected the extracted device and performance parameters. With a 1000nm long pass filter, a dark I-V was obtained since only the bottom Ge subcell was activated.
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Zandbergen, Sander, and Sander Zandbergen. "Light-Matter Interactions in Various Semiconductor Systems." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/624528.
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Semiconductors provide an interesting platform for studying light-matter interactions due to their unique electrically conductive behavior which can be deliberately altered in useful ways with the controlled introduction of confinement and doping, which changes the electronic band structure. This area of research has led to many important fundamental scientific discoveries that have in turn spawned a plethora of applications in areas such as photonics, microscopy, single-photon sources, and metamaterials. Silicon is the prevalent semiconductor platform for microelectronics because of its cost and electrical properties, while III-V materials are optimal for optoelectronics because of the ability to engineer a direct bandgap and create versatile heterojunctions by growing binary, ternary, or quaternary compounds.
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Hurle, Bernard Alfred. "The charge coupled device as a low light detector in beam foil spectroscopy." Thesis, University of Kent, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332296.
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Coelho, Rodrigo Santiago. "Joining of light-weight materials by friction stir welding and laser beam welding." Berlin Bochum Dülmen London Paris Europ. Univ.-Verl, 2008. http://d-nb.info/994359489/04.
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Matta, Samuel. "AlGaN quantum dots grown by molecular beam epitaxy for ultraviolet light emitting diodes." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS042/document.
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Ce travail porte sur la croissance par épitaxie sous jets moléculaires (EJM) et sur les propriétés structurales et optiques de boîtes quantiques (BQs) AlyGa1-yN insérées dans une matrice AlxGa1-xN (0001). L’objectif principal est d’étudier le potentiel des BQs en tant que nouvelle voie pour la réalisation d’émetteurs ultraviolets (UV) efficaces.Tout d'abord, nous avons étudié la croissance des BQs GaN en utilisant soit une source plasma (N2, appelée PAMBE) soit une source ammoniac (NH3, appelée NH3-MBE) afin de choisir la meilleure approche pour former les BQs les plus efficaces. Il a été montré que le procédé de croissance est mieux contrôlé en utilisant l’approche PAMBE, conduisant à la croissance de BQs GaN avec des densités plus élevées, une meilleure uniformité en taille et des intensités de photoluminescence (PL) jusqu’à trois fois plus élevées. En outre, l'influence de la contrainte épitaxiale sur le processus d'auto-assemblage des BQs a été étudiée en fabriquant des BQs GaN sur différentes couche tremplins d’AlxGa1-xN (avec 0,5 ≤ x ≤ 0,7). Nous avons montré que des BQs avec des densités plus élevées et des hauteurs plus faibles sont formées en augmentant le désaccord de paramètre de maille (c.à.d en utilisant des tremplins avec xAl plus élevé). Cependant, les mesures de photoluminescence (PL) indiquent un fort décalage de l'énergie d'émission vers le rouge lorsque xAl augmente, en raison de l'augmentation de la discontinuité du champ électrique interne de 3 à 5,3 MV/cm.Ensuite, des études approfondies sur les conditions de croissance et les propriétés optiques des BQs Al0,1Ga0,9N / Al0,5Ga0,5N ont été présentées, montrant les différents défis pour fabriquer des BQs efficaces. L’optimisation de la procédure de croissance, notamment l’étape de recuit post-croissance, a montré une modification de la forme des BQs. Plus précisément, un changement d’une forme allongée (pour un recuit à 740 °C), à une forme symétrique (pour un recuit à une température proche de ou supérieure à 800°C) a été observé. En plus, une bande d’émission supplémentaire vers les plus grandes longueurs d’onde a également été observée pour les BQs formées avec un recuit à 740°C. Cette bande a été attribuée à une fluctuation de composition des BQs, induisant la formation d’une famille additionnelle de BQs avec des hauteurs plus grandes et une compostions en Al inférieure à 10 %, estimée proche de l’alliage binaire GaN. Enfin, il a été démontré qu’en faisant un recuit à plus haute température (≥ 800°C), l’émission de PL de cette famille supplémentaire de BQs (BQs riche en Ga ou (Al)GaN) diminue très fortement. De plus, cette étape de recuit impacte fortement la forme des BQs et a conduit à une amélioration de leur efficacité radiative d’un facteur 3. Ensuite, la variation de la composition en Al des BQs AlyGa1-yN (0,1 ≤ y ≤ 0,4), ainsi que la quantité de matière déposée ont permis d’évaluer la gamme de longueurs d’onde d’émission accessibles. En ajustant les conditions de croissance, l’émission des BQs a été déplacée de l’UVA vers l’UVC, atteignant une émission autour de 270 - 275 nm (pour les applications de purification de l’eau et de l’air) avec des rendements radiatifs élevés. Les mesures de photoluminescence résolue en temps (TRPL), combinées avec les mesures de PL en fonction de la température, nous ont permis de déterminer les efficacités quantiques internes (IQE) des BQs GaN / AlxGa1-xN (0001). Des valeurs d’IQE comprises entre 50 % et 66 % ont été obtenues à basse température, avec la possibilité d’atteindre un rapport d’intensité intégré de PL, entre 300 K et 9 K, allant jusqu’à 75 % pour les BQs GaN et 46 % pour les BQs AlyGa1-yN (contre 0,5 % pour des structures équivalents à base de puits quantiques).Enfin, nous avons montré la possibilité de fabriquer des DELs à base de BQs (Al,Ga)N couvrant une grande gamme de longueurs d’onde allant du bleu-violet jusqu’à l’UVB (de 415 nm à 305 nm)This PhD deals with the epitaxial growth, structural and optical properties of AlyGa1-yN quantum dots (QDs) grown on AlxGa1-xN (0001) by molecular beam epitaxy (MBE), with the aim to study their potential as a novel route for efficient ultraviolet (UV) emitters.First, we have studied the growth of GaN QDs using either plasma MBE (PAMBE) or ammonia MBE (NH3-MBE) to find the most adapted nitrogen source for the fabrication of UV emitting QDs. It was shown that the growth process is better controlled using PAMBE, leading to the growth of GaN QDs with higher densities, better size uniformity and up to three times higher photoluminescence (PL) intensities. Also, the influence of the epitaxial strain on the QD self-assembling process was studied by fabricating GaN QDs on different AlxGa1-xN surfaces (with 0.5 ≤ x ≤ 0.7). We showed that QDs with higher densities and smaller sizes (heights) are formed by using a larger lattice-mismatch (i.e. a higher xAl composition). However, photoluminescence (PL) measurements indicated a strong redshift in the emission energy as the Al content of the AlxGa1-xN template increases due to the increase of the internal electric field discontinuity from 3 to 5.3 MV/cm.Next, in-depth investigations of the growth conditions and optical properties of Al0.1Ga0.9N QDs / Al0.5Ga0.5N were done presenting the different challenges to be solved to grow efficient QDs. Changing the growth procedure, especially the post-growth annealing step, has shown a modification of the QD shape from elongated QDs, formed with an annealing at 740°C, to symmetric QDs, formed with an annealing at a temperature around or above 800°C. An additional band emission at lower energies was also observed for QDs grown with a lower annealing temperature (740°C). This additional band emission was attributed to the formation of QDs with higher heights and a reduced Al composition less than the nominal one of 10 % (i.e. forming Ga-rich QDs). The influence of the annealing step performed at higher temperature has been shown to strongly decrease the PL emission from this additional QD family. In addition, this annealing step strongly impacted the QD shape and led to an improvement of the QD radiative efficiency by a factor 3. Then, the AlxGa1-xN barrier composition (0.5 ≤ x ≤ 0.7), the AlyGa1-yN QD composition (0.1 ≤ y ≤ 0.4) as well as the deposited amount were varied in order to assess the range of accessible emission energies. Also, the influence of varying the AlxGa1-xN barrier composition on the QD formation was studied. By varying these growth conditions, the QD wavelength emission was shifted from the UVA down to the UVC range, reaching a minimum wavelength emission of 270 - 275 nm (for water and air purification applications) with a high radiative efficiency. Time resolved photoluminescence (TRPL) combined with temperature dependent PL measurements enabled us to determine the internal quantum efficiencies (IQE) of AlyGa1-yN QDs / AlxGa1-xN (0001). IQE values between 50 % and 66 % were found at low temperature, combined with the ability to reach a PL integrated intensity ratio, between 300 K and 9 K, up to 75 % for GaN QDs and 46 % for AlyGa1-yN QDs (versus 0.5 % in a similar quantum well structure emitting in the UVC range).Finally, the demonstration of AlyGa1-yN QD-based light emitting diode prototypes, emitting in the whole UVA range, using GaN and Al0.1Ga0.9N QDs, and in the UVB range down to 305 nm with Al0.2Ga0.8N QDs active regions, was shown
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Breitwieser, Matthias, Friedemann D. Heinz, Andreas Büchler, Martin Kasemann, Jonas Schön, Wilhelm Warta, and Martin C. Schubert. "Analysis of solar cell cross sections with micro-light beam induced current (µLBIC)." Elsevier, 2014. https://publish.fid-move.qucosa.de/id/qucosa%3A72456.
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A highly resolving micro-light beam-induced current (µLBIC)-system is presented in this work. Based on the laser excitation via an optical microscope, current values can be measured with sub-micron precision. We show, that this non-destructive, light-based approach delivers superior results to a reference electron microscope based electron beam induced current method concerning contrast and robustness towards reflection differences, whereas no vacuum is needed, no charging effects can occur and equal resolution is achieved. µLBIC allows therefore mapping of pn-junctions at silicon solar cell cross sections. By combination of µLBIC with other measurement methods in the same setup, such as micro-Raman spectroscopy, complementary microscopic information about material stress or crystallinity and electronic properties at the same region of interest on the sample is revealed. By applying µLBIC for analyzing silicon solar cross sections, two characterization examples of current technological relevance are presented: enhanced dopant diffusion along grain boundaries between grains with different orientations is quantified and the impact of a nickel silicide spike on local charge collection quality is studied.
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Mazilu, Michael, Tom Vettenburg, Martin Ploschner, Ewan M. Wright, and Kishan Dholakia. "Modal beam splitter: determination of the transversal components of an electromagnetic light field." NATURE PUBLISHING GROUP, 2017. http://hdl.handle.net/10150/625761.
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The transversal profile of beams can always be defined as a superposition of orthogonal fields, such as optical eigenmodes. Here, we describe a generic method to separate the individual components in a laser beam and map each mode onto its designated detector with low crosstalk. We demonstrate this with the decomposition into Laguerre-Gaussian beams and introduce a distribution over the integer numbers corresponding to the discrete orbital and radial momentum components of the light field. The method is based on determining an eigenmask filter transforming the incident optical eigenmodes to position eigenmodes enabling the detection of the state of the light field using single detectors while minimizing cross talk with respect to the set of filter masks considered.
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Bezuidenhout, Lucian John-Ross. "On the characterisation of photovoltaic device parameters using light beam induced current measurements." Thesis, Nelson Mandela Metropolitan University, 2015. http://hdl.handle.net/10948/d1020282.
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Light Beam Induced Current (LBIC) measurement is a non-destructive technique used to perform localized characterization of solar cells using a light beam as a probe. The technique allows the determination of local photo response of a cell, the electrical parameters and defects that occur in the individual solar cell. The semiconductor materials used to create solar cells are not always defect free and these defects reduce the electrical performance of the device. It is therefore important to use a system that will allow the characterization and extract the solar cell parameters as can be done using the LBIC system. By analysing these parameters and cell defects, further studies can be done to enhance the cell’s lifetime and hence its efficiency. Light beam induced current (LBIC) is a technique that focuses light onto a solar cell device and thus creating a photo-generated current that can be measured in the external circuit for analyses. By scanning this beam probe across a solar cell while measuring the current-voltage characteristics, a map of various parameters can be obtained. This thesis presents the design of the LBIC system, the software interfacing of the data acquisition system and local photo-response within different solar cell technologies. In addition, this thesis represent two curve fitting algorithms namely: the Gradient Descent Optimisation and the Differential Evolution used for the extraction of solar cell device parameters. The algorithms are based on the one-diode solar cell model and make use of the light generated current-voltage (I-V) data obtained from the LBIC system. Different solar cell technologies namely; single crystalline (c-Si) and multicrystalline silicon (mc-Si) was used for analysis. LBIC maps and I-V characteristics of both technologies was obtained. The LBIC maps shows performance degrading defects present in the bulk and the surface of the solar cells as a function of spatial distribution. These localised defects acts as trapping mechanism for the charge carriers and therefore limits recombination within the solar cell and thus decreasing the performance of the solar cell device. The resulting I-V characteristics obtained from the LBIC system were used to determine the performance parameters using the two algorithms. The resultant effect of these parameters on the performance of the solar cells was observed. The overall results showed that LBIC is a useful tool for identifying and characterising defects in solar cells.
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Liang, Yu-Han. "Deep Ultraviolet Light Emitters Based on (Al,Ga)N/GaN Semiconductor Heterostructures." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1008.
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Deep ultraviolet (UV) light sources are useful in a number of applications that include sterilization, medical diagnostics, as well as chemical and biological identification. However, state-of-the-art deep UV light-emitting diodes and lasers made from semiconductors still suffer from low external quantum efficiency and low output powers. These limitations make them costly and ineffective in a wide range of applications. Deep UV sources such as lasers that currently exist are prohibitively bulky, complicated, and expensive. This is typically because they are constituted of an assemblage of two to three other lasers in tandem to facilitate sequential harmonic generation that ultimately results in the desired deep UV wavelength. For semiconductor-based deep UV sources, the most challenging difficulty has been finding ways to optimally dope the (Al,Ga)N/GaN heterostructures essential for UV-C light sources. It has proven to be very difficult to achieve high free carrier concentrations and low resistivities in high-aluminum-containing III-nitrides. As a result, p-type doped aluminum-free III-nitrides are employed as the p-type contact layers in UV light-emitting diode structures. However, because of impedance-mismatch issues, light extraction from the device and consequently the overall external quantum efficiency is drastically reduced. This problem is compounded with high losses and low gain when one tries to make UV nitride lasers. In this thesis, we provide a robust and reproducible approach to resolving most of these challenges. By using a liquid-metal-enabled growth mode in a plasma-assisted molecular beam epitaxy process, we show that highly-doped aluminum containing III-nitride films can be achieved. This growth mode is driven by kinetics. Using this approach, we have been able to achieve extremely high p-type and n-type doping in (Al,Ga)N films with high aluminum content. By incorporating a very high density of Mg atoms in (Al,Ga)N films, we have been able to show, by temperature-dependent photoluminescence, that the activation energy of the acceptors is substantially lower, thus allowing a higher hole concentration than usual to be available for conduction. It is believed that the lower activation energy is a result of an impurity band tail induced by the high Mg concentration. The successful p-type doping of high aluminum-content (Al,Ga)N has allowed us to demonstrate operation of deep ultraviolet LEDs emitting at 274 nm. This achievement paves the way for making lasers that emit in the UV-C region of the spectrum. In this thesis, we performed preliminary work on using our structures to make UV-C lasers based on photonic crystal nanocavity structures. The nanocavity laser structures show that the threshold optical pumping power necessary to reach lasing is much lower than in conventional edge-emitting lasers. Furthermore, the photonic crystal nanocavity structure has a small mode volume and does not need mirrors for optical feedback. These advantages significantly reduce material loss and eliminate mirror loss. This structure therefore potentially opens the door to achieving efficient and compact lasers in the UV-C region of the spectrum.
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Muhammad, Fikri. "Multichannel +/-1.16 kV arbitrary waveform generator for driving multistage ferroelectric laser-beam-deflector." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.16 Mb., 70 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435919.
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Taylor, Kevin B. "Dual-beam multiple-wavelength light transmittance measurement for particle sizing in rocket motor plumes." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA272491.
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Renkoski, Timothy Eli. "Study of a high frequency electro-optic beam deflector utilizing reflection-based velocity matching /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1422958.
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Ichino, Kunio. "Molecular beam epitaxy and characterization of heterostructures with ZnCdSSe quaternary alloys for light-emitting devices." Kyoto University, 1993. http://hdl.handle.net/2433/74649.
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Morris, Jill E. "Studies of novel beam shapes and applications to optical manipulation." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1699.
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In this thesis an investigation into novel beams and optical manipulation is presented. Sculpting the phase profile of a Gaussian beam can result in the generation of a beam with unusual properties. Described in this thesis are optical vortices, Bessel beams and Airy beams. Additionally, optical manipulation was investigated using both novel beams and Gaussian beams with an emphasis on the use of a broad bandwidth laser source. The generation of multiple broadband optical trap sites was explored, and the transfer of orbital angular momentum from a broadband optical vortex to trapped microspheres was demonstrated. An introduction to the thesis and an overview of laser sources used for optical manipulation is presented in Chapters 1 and 2. Chapters 3 and 4 detail the background of optical manipulation and novel beam shaping. In Chapter 5, an investigation into the generation of multiple broadband optical trap sites is presented. Chapter 6 details the use of a ‘white light’ optical vortex to transfer orbital angular momentum to trapped microspheres. Chapter 7 presents the results of an investigation carried out using a supercontinuum source to characterise the wavelength and spatial coherence dependence of the properties of an optical Airy beam. The use of a monochromatic laser to generate Bessel beams that propagate along curved trajectories is detailed in Chapter 8. Chapter 9 summarises the thesis and suggests future work.
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Wu, Guimin. "Wavefront Control With Realistic Spatial Light Modulator in a Multi-aperture Imager." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1355243952.
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Lutkenhaus, Jeffrey Ryan. "Local Phase Manipulation for Multi-Beam Interference Lithography for the Fabrication of Two and Three Dimensional Photonic Crystal Templates." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955084/.
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In this work, we study the use of a spatial light modulator (SLM) for local manipulation of phase in interfering laser beams to fabricate photonic crystal templates with embedded, engineered defects. A SLM displaying geometric phase patterns was used as a digitally programmable phase mask to fabricate 4-fold and 6-fold symmetric photonic crystal templates. Through pixel-by-pixel phase engineering, digital control of the phases of one or more of the interfering beams was demonstrated, thus allowing change in the interference pattern. The phases of the generated beams were programmed at specific locations, resulting in defect structures in the fabricated photonic lattices such as missing lattice line defects, and single-motif lattice defects in dual-motif lattice background. The diffraction efficiency from the phase pattern was used to locally modify the filling fraction in holographically fabricated structures, resulting in defects with a different fill fraction than the bulk lattice. Through two steps of phase engineering, a spatially variant lattice defect with a 90° bend in a periodic bulk lattice was fabricated. Finally, by reducing the relative phase shift of the defect line and utilizing the different diffraction efficiency between the defect line and the background phase pattern, desired and functional defect lattices can be registered into the background lattice through direct imaging of the designed phase patterns.
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Moloney, Jerome V., Kolja Schuh, Paris Panagiotopoulos, M. Kolesik, and S. W. Koch. "Long range robust multi-terawatt MWIR and LWIR atmospheric light bullets." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626498.
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There is a strong push worldwide to develop multi-Joule femtosecond duration laser pulses at wavelengths around 3.5-4 and 9-11 mu m within important atmospheric transmission windows. We have shown that pulses with a 4 mu m central wavelength are capable of delivering multi-TW powers at km range. This is in stark contrast to pulses at near-IR wavelengths which break up into hundreds of filaments with each carrying around 5 GW of power per filament over meter distances. We will show that nonlinear envelope propagators fail to capture the true physics. Instead a new optical carrier shock singularity emerges that can act to limit peak intensities below the ionization threshold leading to low loss long range propagation. At LWIR wavelengths many-body correlations of weakly-ionized electrons further suppress the Kerr focusing nonlinearity around 10 mu m and enable whole beam self-trapping without filaments.
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Guler, Urcan. "Localized Surface Plasmons In Metal Nanoparticles Engineered By Electron Beam Lithography." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610934/index.pdf.
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In this study, optical behavior of metal nanoparticles having dimensions smaller
than the wavelength of visible light is studied experimentally and numerically.
Gold (Au) and silver (Ag) nanoparticles are studied due to their superior optical
properties when compared to other metals. A compact code based on Discrete
Dipole Approximation (DDA) is developed to compute extinction efficiencies of
nanoparticles with various different properties such as material, dimension and
geometry. To obtain self consistent nanoparticle arrays with well defined
geometries and dimensions, Electron Beam Lithography (EBL) technique is
mainly used as the manufacturing method. Dose parameters required to produce
nanoparticles with dimensions down to 50 nm over substrates with different
electrical conductivities are determined. Beam current is found to affect the doseV
size relation. The use of thin Au films as antistatic layer for e-beam patterning
over insulating substrates is considered and production steps, involving
instabilities due to contaminants introduced to the system during additional
removal steps, are clarified. 4 nm thick Au layer is found to provide sufficient
conductivity for e-beam patterning over insulating substrates. An optical setup
capable of performing transmittance and reflectance measurements of samples
having small areas patterned with EBL is designed. Sizes of the metal
nanoparticles are determined by scanning electron microscope (SEM) and spectral
data obtained using the optical setup is analyzed to find out the parameters
affecting the localized surface plasmon resonances (LSPR). Arrays of particles
with diameters between 50 &ndash200 nm are produced and optically analyzed. Size and shape of the nanoparticles are found to affect the resonance behavior. Furthermore, lattice constants of the particle arrays and surrounding medium are also shown to influence the reflectance spectra. Axes with different lengths in ellipsoidal nanoparticles are observed to cause distinguishable resonance peaks when illuminated with polarized light. Peak intensities obtained from both polarizations are observed to decrease under unpolarized illumination. Binary systems consisting of nanosized particles and holes provided better contrast for transmitted light.
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Jiang, Chunxu. "Stability analysis of light gauge steel members using the finite element method and the generalized beam theory." Thesis, University of Salford, 1994. http://usir.salford.ac.uk/43027/.
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In this thesis a finite element programme for material and geometric nonlinear analysis, has been modified with pre- and post-data processing and eigenvalue solution. More efficient methods to solve elastic and inelastic eigenvalue and eigenvectors have been developed to deal with stability problems in structures with arbitrary shape, irregular stiffness, loads and boundary conditions. The Generalized Beam Theory (GBT) with the facilities of elastic spring restraints, buckling under coupled loads, different load locations has been developed and programmed by the author. It has been applied to reveal the basic behaviour and the interaction between the modes of light gauge steel members. It has been found that the AISI design approach with elastic bucking stresses obtained using GBT can be used to correctly predict the strength of compression thin-walled columns. Three different types of widely used light gauge steel members, namely rack columns, purlins and decks, have been analyzed using both FEM and GBT. The comparison of results from the numerical analyses and comprehensive tests agrees well. The author has risen to the challenge of complicated buckling problems and a pseudo-plastic design procedure for a continuous purlins and roof decks has been established in order to make the best us of the materials. Through the highly complex analyses, some important conclusions for composite deck profiles in the wet concrete stage have been obtained. The ECCS and AISI design approaches for bending have been found to be conservative when the deck is subject to plastic buckling or strength failure. The calculation of the ultimate web crippling load without consideration of bending moment is awkward and further light is shed on this topical problem. The influence of dimples in reducing the deck bending resistance mainly depends on the flange slenderness.
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Oto, Takao. "Emission Mechanisms in Al-rich AlGaN Quantum Wells toward Deep Ultraviolet Light Emitters by Electron Beam Pumping." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188542.
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Myronidi, Despoina. "LIGHT-BEAT: REACTIVE LIGHT FOR THE EMOTIONAL COMFORT OF NEWBORN BABIES." Thesis, KTH, Ljusdesign, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297961.
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This is a project-based thesis focusing on the investigation of topics related to human newborns and the factors found in their surrounding environment that need to be assessed so as to provide them with a feeling comfort. The objective is to boost their emotional development by the means of light in a close relation to sound so as to provide them with a type of intelligence allowing them to normally interact within a society during their adult life, reassuring social equality and eliminating potential social exclusion due to unexpected behaviours. After researching topics to have a better understanding of the newborn baby and its enclosing environment, a luminaire design solution -functioning with a reactive scheme performed with integrated sound sensors- provided further results to the main topic investigation. The conceptual scheme for the product development was inspired by the connection between the newborn and their life-giver, closely linked to the cross-modality of sensory development before and after birth. Additional results were obtained with light measurement assessments and a parent survey targeting both the intended light quality subjective evaluations and the marketing strength of the designed product. This survey was used -along with other means- as a design evaluation tool at the final stage of the design process. Potential further improvements as well as considerations for a distinct spatial application are discussed in the final part of the thesis. The sustainability aspect covered within this degree project is closely linked to good physical and mental health aspects, clean energy use and efficiency achieved by the integration of input sound sensors and controls, and conscious production and consumption by the proposal of low global footprint materials for the luminaire design. In the conclusions, an overall summary of the thesis outcomes is presented and further research is proposed regarding both the main topic investigation as well as a greater user category that can be related to the light metric assessments that were carried out for this research.
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Tovar, Anthony Alan. "Off-axis multimode light beam propagation in tapered lenslike media including those with spatial gain or loss variation." PDXScholar, 1988. https://pdxscholar.library.pdx.edu/open_access_etds/3839.
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The propagation of light beams in inhomogeneous dielectric media is considered. The derivation begins with first principles and remains general enough to include off-axis asymmetric multimode input beams in tapered lenslike media with spatial variations of gain or loss. The tapering of lenslike media leads to a number of important applications. A parabolic taper is proposed as a model for a heated axially stretched fiber taper, and beams in such media are fully characterized. Other models are proposed by the concatenation of a parabola with other taper functions.
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Petenev, Yuriy. "Analysis of injection and recovery schemes for ERL based light source." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2014. http://dx.doi.org/10.18452/17014.
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Helmholtz Zentrum Berlin (HZB) baut seit 2011 eine Testanlage Energy Recovery Linac (ERL) Project – BERLinPro. Das Ziel dieses Projektes ist den hohen Strom und hohe Brillanz von dem Elektronenstrahl in einem ERL zu demonstrieren. Die angestrebten Strahlparameter sind vergleichbar mit den Parametern von e.g. zukünftigen ERL-basierten Lichtquellen. Eine von solchen Anlagen ist Femto-Science Factory (FSF), die am HZB konzipiert wurde. FSF ist eine Lichtquelle in Röntgenbereich auf Basis von einem mehrumläufigen ERL mit zweistüfiger Injektion und Energie von einigen GeV. Die Quelle soll Diffraktionslimitiert sein und kurze (Femtosekundenbereich) Lichtpulse erzeugen. Die durchschnittliche und spitzen- Brillanz soll mindesten eine Größenordnung höher liegen als die Brillanz der modernen Speicherring-basierten Lichtquellen. Ein Überblick von BERLinPro und FSF ist gegeben. Eine potentielle Schwäche von ERL besteht in Strahlinstabilitäten, insbesondere regenerative Beam Break Up (BBU). Die Instabilität kann den erreichbaren durchschnittlichen Strom in einem ERL begrenzen. Der Grenzstrom von der BBU für BERLinPro ist berechnet in der Dissertation. Vergleich von zwei Linacs mit zwei verschiedenen supraleitenden Kavitätendesigns ist vorgestellt. Drei Methoden für Strahlstabilisierung (Einfluss von Strahlrotation mit einem Soleniod, Pseudoreflektor, und Tripleten von Quadrupolen in dem Linac auf den Grenzstrom) sind untersucht. Analytische Lösungen für die Twiss-Parameter wurden gefunden für die beste Linacoptik mit und ohne zusätzliche optische Elemente. Zukünftige große ERLs können unterschiedliche Beschleunigungsschemen benutzen. Diese Dissertation vergleicht drei Schemas: unmittelbare Injektion in einen 6 GeV Linac; zweistufige Injektion in einen 6 GeV Linac; und zweistufige Injektion in einen mehrumläufigen Beschleuniger mit geteiltem Hauptlinac in zwei 1 GeV Linacs. Der Basis für den Vergleich ist die Vollkostenanalyse sowie erreichbarer Grenzstrom von den Instabilitäten.In January 2011 Helmholtz-Zentrum Berlin officially started the realization of the Berlin Energy Recovery Linac (ERL) Project – BERLinPro. The goal of this compact ERL is to develop the accelerator physics and technology required to accelerate a high-current (100 mA) low emittance beam. The parameters are desired for future large scale facilities based on ERLs, e.g. ERL-based synchrotron light sources. One of such large scale facilities is in the design phase at Helmholtz-Zentrum Berlin. This facility is called Femto-Science Factory (FSF). It is a GeV-scale multi-turn ERL-based light source. This light source will operate in the diffraction limited regime for X-rays and offer a short length of a light pulse in the femtosecond region. The average and peak brightness will be at least an order of magnitude higher than achievable from storage rings. In this work an overview of these two projects is given. One potential weakness of the Energy Recovery Linacs is a regenerative form of BBU – transverse beam break up instability. This instability can limit a beam current. In this work the threshold current of the BBU instability was calculated for BERLinPro. The comparison of two linacs based on different types of superconducting cavities is made. Different methods of BBU suppression are investigated (e.g. the influence of solenoid, pseudo-reflector and quadruple triplets in the linac structure on the BBU threshold). Analytic solutions of the Twiss parameters are used to find the best optic in the linac with and without external focusing are presented. Large scale ERL facilities can be realized on different schemes of beam acceleration. This dissertation compares a direct injection scheme with acceleration in a 6 GeV linac, a two-stage injection with acceleration in a 6 GeV linac and a multi-turn (3-turn) scheme with a two-stage injection and two main 1 GeV linacs. The key points of the comparison were total costs and BBU instability. Linac optic solutions are presented.
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Hassan, Safaa. "Optical Property Study of 2D Graded Photonic Super-Crystals for Photon Management." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1703318/.
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In this dissertation, we study the optical property of 2D graded photonic super-crystals (GPSCs) for photon management. We focused primarily on manipulation and control of light by using the newly discovered GPSCs which present great opportunity for electromagnetic wave control in photonic devices. The GPSC has been used to explore the superior capability of improving the light extraction efficiency of OLEDs. The enhancement of extraction efficiency has been explained in term of destructive interference of surface plasmon resonance and out-coupling of surface plasmon through phase matching provided by GPSC and verified by e-field intensity distributions. A large light extraction efficiency up to 75% into glass substrate has been predicted through simulation. We also study the light trapping enhancement in GPSCs. Broadband, wide incident angle, and polarization independent light trapping enhancement is achieved in silicon solar cells patterned with the GPSCs. In addition, novel 2D GPSCs were fabricated using holographic lithography through the interference lithography by two sets of multiple beams arranged in a cone geometry using a spatial light modulator (SLM). Finally, we also report a fabrication of GPSCs with a super-cell size of 12a×12a by using e-beam lithography. Diffraction pattern from GPSCs reveals unique diffraction properties. In an application aspect, light emitting diode arrays can be replaced by a single light emitting diode shinning onto the diffraction pattern for a uniform fluorescence.
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Rudhall, Andrew Peter. "Ultrashort laser pulse shaping for novel light fields and experimental biophysics." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3682.
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Broadband spectral content is required to support ultrashort pulses. However this broadband content is subject to dispersion and hence the pulse duration of corresponding ultrashort pulses may be stretched accordingly. I used a commercially-available adaptive ultrashort pulse shaper featuring multiphoton intrapulse interference phase scan technology to characterise and compensate for the dispersion of the optical system in situ and conducted experimental and theoretical studies in various inter-linked topics relating to the light-matter interaction. Firstly, I examined the role of broadband ultrashort pulses in novel light-matter interacting systems involving optically co-trapped particle systems in which inter-particle light scattering occurs between optically-bound particles. Secondly, I delivered dispersion-compensated broadband ultrashort pulses in a dispersive microscope system to investigate the role of pulse duration in a biological light-matter interaction involving laser-induced cell membrane permeabilisation through linear and nonlinear optical absorption. Finally, I examined some of the propagation characteristics of broadband ultrashort pulse propagation using a computer-controlled spatial light modulator. The propagation characteristics of ultrashort pulses is of paramount importance for defining the light-matter interaction in systems. The ability to control ultrashort pulse propagation by using adaptive dispersion compensation enables chirp-free ultrashort pulses to be used in experiments requiring the shortest possible pulses for a specified spectral bandwidth. Ultrashort pulsed beams may be configured to provide high peak intensities over long propagation lengths, for example, using novel beam shapes such as Bessel-type beams, which has applications in biological light-matter interactions including phototransfection based on laser-induced cell membrane permeabilisation. The need for precise positioning of the beam focus on the cell membrane becomes less strenuous by virtue of the spatial properties of the Bessel beam. Dispersion compensation can be used to control the temporal properties of ultrashort pulses thus permitting, for example, a high peak intensity to be maintained along the length of a Bessel beam, thereby reducing the pulse energy required to permeabilise the cell membrane and potentially reduce damage therein.
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Provence, Sydney R. "Next generation mid-wave infrared cascaded light emitting diodes: growth of broadband, multispectral, and single color devices on GaAs and integrated circuits." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/5827.
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InAs/GaSb superlattices are an attractive material system for infrared light emitting diodes, due to the ability to tune the band gap throughout most of the infrared regime. A key consideration in the epitaxial growth of these heterostructures is crystalline material quality. In developing thick layers of epitaxially grown material, there are moderate amounts of elastic strain that can be incorporated into a heterostructure, beyond which deformations will form that will alleviate the lattice mismatch. This thesis investigates the optical and electronic properties of lattice-mismatched and strained materials through the study of thick dual-color light emitting diodes, broadband light emitting diodes, and InAs/GaSb superlattice devices developed on GaAs substrates and GaAs integrated circuits.
A dual-color infrared light emitting diode is demonstrated emitting in the mid-wave infrared band at 3.81 μm and 4.72 μm. The design of the device stacks two independently operable InAs/GaSb superlattices structures on top of one another, so that 10 μm of material is grown with molecular beam epitaxy. Each layer is lattice-matched to a GaSb substrate. At quasi-continuous operation, radiances of 5.48 W/cm2-sr and 2.67 W/cm2-sr are obtained.
A broadband light emitting diode spanning the mid-wave infrared is demonstrated with eight stages of InAs/GaSb superlattices individually tuned to a different color. The performance of the device is compared with an identical eight stage device emitting in the middle of the mid-wave infrared. The emission of the fabricated broadband device spans from 3.2 μm to 6 μm with peak radiance of 137.1 mW/cm2-sr.
Growth of antimonide-based devices on GaAs is desirable to the relative transparency of semi-insulating substrates throughout the infrared, and as semi-insulating GaSb substrates are not available. The growth of bulk GaSb on GaAs is explored through different techniques in order to confine relaxation due to lattice mismatch strain to the GaSb/GaAs interface. A low temperature nucleation technique with a thin GaSb wetting layer is found to have the best overall surface morphology, although screw dislocations are a prominent feature on all samples. The dislocations and overall surface roughness are not found to destructively impact the overall device quality, as four stage InAs/GaSb superlattice devices grown on GaAs substrates are found to have superior electroluminescent emission and external quantum efficiency compared to an identical device grown on a GaSb substrate due to the higher substrate transparency and superior thermal properties.
Epitaxy on electronics growth techniques on GaAs integrated circuits are developed to bypass the hybridization process in light emitting diode development. Chips obtained from Quorvo, Inc. are found to endure ultra-high vacuum molecular beam epitaxy environment at higher temperatures with silicon nitride encapsulation, and a low temperature oxide removal technique is developed using an atomic hydrogen source. Chemical-mechanical polishing techniques are developed to create an “epi-ready” substrate surface. Ultimately, no photoluminescent emission is observed from InAs/GaSb superlattices grown on GaAs integrated circuits, although electroluminescent emission is still possible.
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Stellinga, Daniël Pieter. "Shaping light beams with dielectric metasurfaces." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/13225/.
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With the advent of techniques such as Stimulated Emission Depletion Microscopy (STED) and light sheet microscopy, the generation of specialised light beams has become an exciting field. However, while very effective methods of generating such beams exist, the components necessary to do so are generally large and cumbersome. Metasurfaces promise the replacement of these traditional bulky optical elements with sub-wavelength thick and flat alternatives, paving the way for integration into microscale form factors. Metasurfaces commonly use a distribution of nanoscale resonant elements to engineer a phase plate that shapes light through the Huygens' principle, allowing them to mimic and improve upon traditional optics. Initially, plasmonic resonant elements were explored by the community, but their dissipative losses have severely limited the efficiency of these devices. Here I discuss my work on the development of dielectric sub-wavelength grating based metasurfaces. Four types of metasurface, each using a different manifestation of grating physics are explored: direct phase, polarisation conversion, geometric phase, and active metasurfaces. I show that these different types of metasurface together allow the shaping of a wide variety of beams under a large range of different conditions, while retaining efficiencies on the order of 80-90%. Examples of the beam shapes explored include focused beams, vortex beams, Bessel beams and cylindrical vector beams. The development of high efficiency dielectric metasurfaces brings ultrathin optics closer to practical applications. Their materials and sizes facilitate the integration into previously unavailable form factors, including applications in microfluidics.
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Bevilacqua, Riccardo. "Neutron induced light-ion production from iron and bismuth at 175 MeV." Licentiate thesis, Uppsala University, Applied Nuclear Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-112162.
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Light-ions (protons, deuterons, tritons, 3He and α articles) production in the interaction of 175 MeV neutrons with iron and bismuth has been measured using the Medley setup at the The Svedberg Laboratory (TSL) in Uppsala. These measurements have been conducted in the frame of an international collaboration whose aim is to provide the scientific community with new nuclear data of interest for the development of Accelerator Driven Systems, in the range of 20 to 200 MeV. In this Licentiate Thesis I will present the background for the present experiment, the choice of the measured materials (iron and bismuth) and of the energy range. I will then give a short theoretical description of the involved nuclear reactions and of the model used to compare the experimental results. A description of the neutron facility at TSL and of Medley setup will follow. Monte Carlo simulations of the experimental setup have been performed and some results are here reported and discussed. I will present data reduction procedure and finally I will report preliminary double differential cross sections for production of hydrogen isotopes from iron and bismuth at several emission angles. Experimental data will be compared with model calculations with TALYS-1.0; these show better agreement for the production of protons, while seems to overestimate the experimental production of deuterons and tritons.
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He, Weiyi. "Optical Design of Beam Shaping Optics for Camera Probe and LED Light Illumination Used for Minimally Invasive Abdominal Surgery." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3532.
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The optical design of a LED illuminator and camera imaging system were studied for potential use in a small medical "robotic type" probe to be used for minimally invasive abdominal surgery. Beam shaping optical reflectors were studied to increase the intensity distribution of the LED beam directed toward a close-by target surface. A CMOS/CCD camera and lens was used to image the targeted area. In addition, extensive optical ray tracing simulations were made to predict the intensity patterns. The experimental measurements and ray tracing simulations were in good agreement, and indicated that 20 degree cone reflectors for the LED sources and appropriate micro-lens/CCD chip imaging optics should provide a useful image at a working distance of about 5 cm.
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May, Brelon J. "Investigation and Engineering of the Homogeneity and Current Injection of Molecular Beam Epitaxy Grown III-Nitride Nanowire Ultraviolet Light Emitting Diodes." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546385850422501.
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Ng, Jack Tsz Fai. "Light-induced forces on small particles /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202005%20NG.
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Hollmark, Malin. "Absorbed dose and biological effect in light ion therapy." Doctoral thesis, Stockholm : Medical Radiation Physics, Stockholm university together with KI, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7756.
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Ruffner, David B. "Optical Forces in Complex Beams of Light." Thesis, New York University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3685907.
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Light possesses no mass but can transfer momentum to matter and thus can exert forces. This thesis explores these optical forces, focusing on two surprising discoveries: optical forces arising from the spin angular momentum of light and beams of light that can pull, as well as push.
In the first case, we have shown that non-uniform beams of light can exert a force proportional to the curl of the spin angular momentum density. To show this we have developed a framework for understanding optical momentum in terms of experimental parameters. This framework makes clear that the curl of the spin angular momentum density contributes to the optical linear momentum. Surprisingly, we find that this contribution does not lead to spin-dependent optical forces at the electric dipole level. Experimentally, however, we find that spin-dependent optical forces do indeed act on isotropic microspheres in focused circularly-polarized beams of light. Theoretically, we confirm that spin-dependent forces appear at higher order in multipole scattering, which qualitatively explains the experimental results.
Using the same theoretical framework, we show that beams of light can act as tractor beams that pull illuminated objects upstream against the direction of propagation. We demonstrate this extraordinary effect experimentally with optical conveyor beams. These experiments demonstrate long-range bidirectional transport of colloidal microparticles along propagation invariant beams of light. They show moreover that optical conveyors can move multiple particles simultaneously due to the self-healing properties of these modes of light. Not only do optical conveyors constitute practical realizations of tractor beams, but they also act as stronger traps than conventional optical traps and are less sensitive to particle composition. Axial interference endows optical conveyors with these superb trapping properties, which in turn gives them greater range than conventional optical traps. Our work provides a jumping off point towards subsequent work on long-range optical tractor beams.
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Carnevale, Santino D. "Catalyst-free III-nitride Nanowires by Plasma-assisted Molecular Beam Epitaxy: Growth, Characterization, and Applications." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374066626.
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Voutta, Robert [Verfasser], and T. [Akademischer Betreuer] Baumbach. "Beam heat load investigations with a cold vacuum chamber for diagnostics in a synchrotron light source / Robert Voutta. Betreuer: T. Baumbach." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/110052973X/34.
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Wei, Yu-Lin, and 魏佑霖. "Indoor Positioning System using Polarized Sweeping Light Beam." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/11824117694781451612.
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碩士國立臺灣大學
資訊工程學研究所
104
Benefit from the wide deployment of Light Emitting Diodes (LED), visible light communication technology has become an active research topic full of commercialization potentials. Taking advantage of this recent development, in this thesis, we proposes LiBeamScanner, an indoor positioning system that utilizes only a single custom light bulb and a light sensor to achieve extremely high positioning accuracy. With only a single light bulb as the transmitter, this system can perform extremely accurate positioning in environments without dense deployment of illuminaries. And the system only utilizes a simple light sensor in the receiver rather than a camera, and has low complexity and low energy consumption. This enables our design to be adopted in systems with more stingent constraints such as wearables. At the transmitting side, we borrow the idea of projectors to send information to corresponding location without interfering neighboring areas by controlling LCD pixels to generate narrow light beams, enabling fine-grained indoor positioning. Moreover, we propose a novel design utilizing dual lenses in the transmitter to modulate the information of stand-off distance, i.e. the height information, in the transmitted signals. Evaluation results of our prototype show that the error is less than 5 cm in most cases and the median error does not exceed 2 cm for the 2-dimensional position estimation, and 17 cm for the 3-dimensional position estimation.
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Lee, Yu-Chi, and 李昱麒. "A Beam Splitter of Natural Light Guiding System." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/01483718196634720574.
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碩士國立臺灣科技大學
光電工程研究所
98
In thremmatology, many researches focus on ecological illumination for improving the growing speed of animal or plant. Sunlight has full spectrum so it is the most applicable source. A Natural Light Guiding System includes collecting, transmitting, and lighting parts. In our research, we would like to design a beam splitter in the transmitting part to separate the sunlight into red, green, and blue light for ecological illumination or make up the lack wavelength of the artificial light sources in door. We use high pass and low pass dichroic coatings in the beam splitter to separate the wavelength, and use prismatic structure to design the beam splitter, and use imaging QU method in the design of the non-imaging system beam splitter to control beam angle, and simulate the result of design by optical software.