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Litvin, Igor A. "Intra–cavity laser beam shaping". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4018.
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Thesis (PhD (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: There are many applications where a Gaussian laser beam is not ideal, for example, in areas such as medicine, data storage, science, manufacturing and so on, and yet in the vast majority of laser systems this is the fundamental output mode. Clearly this is a limitation, and is often overcome by adapting the application in mind to the available beam. A more desirable approach would be to create a laser beam as the output that is tailored for the application in mind – so called intra-cavity laser beam shaping. The main goal of intra-cavity beam shaping is the designing of laser cavities so that one can produce beams directly as the output of the cavity with the required phase and intensity distribution. Shaping the beam inside the cavity is more desirable than reshaping outside the cavity due to the introduction of additional external losses and adjustment problems. More elements are required outside the cavity which leads to additional costs and larger physical systems. In this thesis we present new methods for phase and amplitude intra– cavity beam shaping. To illustrate the methods we give both an analytical and numerical analysis of different resonator systems which are able to produce customised phase and intensity distributions. In the introduction of this thesis, a detailed overview of the key concepts of optical resonators is presented. In Chapter 2 we consider the well–known integral iteration algorithm for intra–cavity field simulation, namely the Fox–Li algorithm and a new method (matrix method), which is based on the Fox–Li algorithm and can decrease the computation time of both the Fox–Li algorithm and any integral iteration algorithms. The method can be used for any class of integral iteration algorithms which has the same calculation integrals, with changing integrants. The given method appreciably decreases the computation time of these algorithms and approaches that of a single iteration. In Chapter 3 a new approach to modeling the spatial intensity profile from Porro prism resonators is proposed based on rotating loss screens to mimic the apex losses of the prisms. A numerical model based on this approach is presented which correctly predicts the output transverse field distribution found experimentally from such resonators. In Chapter 4 we present a combination of both amplitude and phase shaping inside a cavity, namely the deployment of a suitable amplitude filter at the Fourier plane of a conventional resonator configuration with only spherical curvature optical elements, for the generation of Bessel–Gauss beams as the output. In Chapter 5 we present the analytical and numerical analyses of two new resonator systems for generating flat–top–like beams. Both approaches lead to closed form expressions for the required cavity optics, but differ substantially in the design technique, with the first based on reverse propagation of a flattened Gaussian beam, and the second a metamorphosis of a Gaussian into a flat–top beam. We show that both have good convergence properties, and result in the desired stable mode. In Chapter 6 we outline a resonator design that allows for the selection of a Gaussian mode by diffractive optical elements. This is made possible by the metamorphosis of a Gaussian beam into a flat–top beam during propagation from one end of the resonator to the other. By placing the gain medium at the flat–top beam end, it is possible to extract high energy in a low–loss cavity.
AFRIKAANSE OPSOMMING: Daar is verskeie toepassings waar ʼn Gaussiese laser bundel nie ideaal is nie, in gebiede soos mediese veld, stoor van data, vervaardiging en so meer, en tog word die meeste laser sisteme in die fundamentele mode bedryf. Dit is duidelik ’n beperking, en word meestal oorkom deur aanpassing van die toepassing tot die beskikbare bundel. ’n Beter benadering sou wees om ʼn laser bundel te maak wat afgestem is op die toepassing - sogenaamde intra-resonator bundel vorming. Die hoofdoel van intra-resonator bundel vorming is om resonators te ontwerp wat direk as uitset kan lewer wat die gewenste fase en intensiteits-distribusie vertoon. Vorming van die bundel in die resonator is voordeliger omdat die vorming buite die resonator tot addisionele verliese asook verstellings probleme bydra. Meer elemente word benodig buite die resonator wat bydra tot hoër koste en groter sisteme. In hierdie tesis word nuwe fase en amplitude intra-resonator bundelvormings metodes voorgestel. Om hierdie metode te demonstreer word analitiese en numeriese analises vir verskillende resonator sisteme wat aangepaste fase en intensiteit distribusies produseer, bespreek. In die inleiding van die tesis word ʼn detailleer oorsig oor die sleutel konsepte van optiese resonators voorgelê. In hoofstuk 2 word die bekende integraal iterasie algoritme vir intraresonator veld simulasie, naamlik die Fox-Li algoritme, en ʼn nuwe metode (matriks metode), wat gebaseer is op die Fox-Li algoritme, en die berekeningstyd van beide die Fox-Li algoritme en enige ander integraal iterasie algoritme verminder. Die metode kan gebruik word om enige klas van integraal iterasie algoritmes wat dieselfde berekenings integrale het, met veranderde integrante (waar die integrand die veld van die lig golf is in die geval van die Fox-Li algoritme, IFTA, en die skerm metode. Die voorgestelde metode verminder die berekeningstyd aansienlik, en is benaderd die van ʼn enkel iterasie berekening. In hoofstuk 3 word ʼn nuwe benadering om die modellering van die ruimtelike intensiteitsprofiel van Porro prisma resonators, gebaseer op roterende verliese skerms om die apeks-verliese van die prismas te benader, voorgestel. ʼn Numeriese model gebaseer op hierdie benadering wat die uitset van die transversale veld distribusie in eksperimentele resonators korrek voorspel, word voorgestel. In hoofstuk 4 word ʼn tegniek vir die generering van Bessel-Gauss bundels deur die gebruik van ʼn kombinasie van amplitude en fase vorming in die resonator en ʼn geskikte amplitude filter in die Fourier vlak van ʼn konvensionele resonator konfigurasie met optiese elemente wat slegs sferiese krommings het, voorgestel. In hoofstuk 5 word die analitiese en numeriese analises van twee nuwe resonator sisteme vir die generering van sogenaamde “flat–top” bundels voorgestel. Beide benaderings lei na ʼn geslote vorm uitdrukking vir die resonator optika wat benodig word, maar verskil noemenswaardig in die ontwerptegniek. Die eerste is baseer op die terug voortplanting van plat Gaussiese bundel, en die tweede op metamorfose van Gaussiese “flat-top” bundel. Ons toon aan dat beide tegnieke goeie konvergensie het, en in die gevraagde stabiele modus lewer. In hoofstuk 6 skets ons die resonator ontwerp wat die selektering van ʼn Gaussiese modus deur diffraktiewe optiese element moontlik maak. Dit word moontlik deur die metamorfose van ’n Gaussiese bundel na ʼn “flat-top” gedurende die voortplanting van die een kant van die resonator na die ander. Deur die wins medium aan die “flat–top” kant van die bundel te plaas word dit moontlik om hoë energie te onttrek in ʼn lae verlies resonator.
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Zeng, Danyong. "ANNULAR BEAM SHAPING AND OPTICAL TREPANNING". Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2593.
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Percussion drilling and trepanning are two laser drilling methods. Percussion drilling is accomplished by focusing the laser beam to approximately the required diameter of the hole, exposing the material to one or a series of laser pulses at the same spot to melt and vaporize the material. Drilling by trepanning involves cutting a hole by rotating a laser beam with an optical element or an x–y galvo-scanner. Optical trepanning is a new laser drilling method using an annular beam. The annular beams allow numerous irradiance profiles to supply laser energy to the workpiece and thus provide more flexibility in affecting the hole quality than a traditional circular laser beam. Heating depth is important for drilling application. Since there are no good ways to measure the temperature inside substrate during the drilling process, an analytical model for optical trepanning has been developed by considering an axisymmetric, transient heat conduction equation, and the evolutions of the melting temperature isotherm, which is referred to as the melt boundary in this study, are calculated to investigate the influences of the laser pulse shapes and intensity profiles on the hole geometry. This mathematical model provides a means of understanding the thermal effect of laser irradiation with different annular beam shapes. To take account of conduction in the solid, vaporization and convection due to the melt flow caused by an assist gas, an analytical two-dimensional model is developed for optical trepanning. The influences of pulse duration, laser pulse length, pulse repetition rate, intensity profiles and beam radius are investigated to examine their effects on the recast layer thickness, hole depth and taper. The ray tracing technique of geometrical optics is employed to design the necessary optics to transform a Gaussian laser beam into an annular beam of different intensity profiles. Such profiles include half Gaussian with maximum intensities at the inner and outer surfaces of the annulus, respectively, and full Gaussian with maximum intensity within the annulus. Two refractive arrangements have been presented in this study. Geometric optics, or ray optics, describes light propagation in terms of rays. However, it is a simplification of optics, and fails to account for many important optical effects such as diffraction and polarization. The diffractive behaviors of this optical trepanning system are stimulated and analyzed based on the Fresnel diffraction integral. Diffraction patterns of the resulting optical system are measured using a laser beam analyzer and compared with the theoretical results. Based on the theoretical and experimental results, the effects of experimental parameters are discussed. We have designed the annular beam shaping optical elements and the gas delivery system to construct an optical trepanning system. Laser drilling experiments are performed on the Stainless Steel-316 (SS 316) plate and the Inconel 718 (IN 718) plate. The geometry of the trepanning holes with different sizes is presented in this study.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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Mi, Yongcui. "Novel beam shaping and computer vision methods for laser beam welding". Licentiate thesis, Högskolan Väst, Avdelningen för produktionssystem (PS), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-16970.
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Laser beam welding has been widely applied in different industrial sectors due to its unique advantages. However, there are still challenges, such as beam positioning in T-joint welding, and gap bridging in butt joint welding,especially in the case of varying gap width along a joint. It is expected that enabling more advanced control to a welding system, and obtaining more in-depth process knowledge could help to solve these issues. The aim of this work is to address such welding issues by a laser beam shaping technology using a novel deformable mirror together with computer vision methods and also to increase knowledge about the benefits and limitations with this approach. Beam shaping in this work was realized by a novel deformable mirror system integrated into an industrial processing optics. Together with a wave front sensor, a controlled adaptive beam shaping system was formed with a response time of 10 ms. The processes were monitored by a coaxial camera with selected filters and passive or active illumination. Conduction mode autogenous bead-on-plate welding and butt joint welding experiments have been used to understand the effect of beam shaping on the melt pool geometry. Circular Gaussian, and elliptical Gaussian shapes elongated transverse to and along the welding direction were studied. In-process melt pool images and cross section micrographs of the weld seams/beads were analyzed. The results showed that the melt pool geometry can be significantly modified by beam shaping using the deformable mirror. T-joint welding with different beam offset deviations relative to the center of the joint line was conducted to study the potential of using machine learning to track the process state. The results showed that machine learning can reach sufficient detection and estimation performance, which could also be used for on-line control. In addition, in-process and multidimensional data were accurately acquired using computer vision methods. These data reveal weaknesses of current thermo-fluid simulation model, which in turn can help to better understand and control laser beam welding. The obtained results in this work shows a huge potential in using the proposed methods to solve relevant challenges in laser beam welding.Lasersvetsning används i stor utsträckning i olika industrisektorer på grund av dess unika fördelar. Det finns emellertid fortfarande utmaningar, såsom rätt positionering av laserstrålen vid genomträngningssvetsning av T-fogar och hantering av varierande spaltbredd längs fogen vid svetsning av stumfogar. Sådana problem förväntas kunna lösas med avancerade metoder för automatisering, metoder som också förväntas ge fördjupade kunskaper om processen. Syftet med detta arbete är att ta itu med dessa problem med hjälp av en teknik för lasereffektens fördelning på arbetsstycket, s.k. beam shaping. Det sker med hjälp av en ny typ av i realtid deformerbar spegel tillsammans med bildbehandling av kamerabilder från processen. För- och nackdelar med detta tillvägagångssätt undersöks.Beam shaping åstadkoms med hjälp av ny typ av deformerbart spegelsystem som integreras i en industriell processoptik. Tillsammans med en vågfrontsensor bildas ett adaptivt system för beam shaping med en svarstid på 10 ms. Processen övervakas av en kamera linjerad koaxialt med laserstrålen. För att kunna ta bilder av svetspunkten belyses den med ljus av lämplig våglängd, och kameran är försedd med ett motsvarande optiskt filter. Försök har utförts med svetsning utan tillsatsmaterial, direkt på plåtar, svetsning utan s.k. nyckelhål, för att förstå effekten av beam shaping på svetssmältans geometri. Gauss fördelade cirkulära och elliptiska former, långsträckta både tvärs och längs svetsriktningen har studerats. Bilder från svetssmältan har analyserats och även mikrostrukturen i tvärsnitt från de svetsade plåtarna. Resultaten visar att svetssmältans geometri kan modifieras signifikant genom beam shaping med hjälp av det deformerbara spegelsystemet. Genomträngningssvetsning av T-fogar med avvikelser relativt foglinjens centrum genomfördes för att studera potentialen i att använda maskininlärning för att fånga processens tillstånd. Resultaten visade att maskininlärning kan nå tillräcklig prestanda för detektering och skattning av denna avvikelse. Något som också kan användas för återkopplad styrning. Flerdimensionell processdata har samlats i realtid och analyserats med hjälp av bildbehandlingsmetoder. Dessa data avslöjar brister i nuvarande simuleringsmodeller,vilket i sin tur hjälper till med att bättre förstå och styra lasersvetsning.Resultaten från detta arbete uppvisar en god potential i att använda de föreslagna metoderna för att lösa relevanta utmaningar inom lasersvetsning.
Till licentiatuppsats hör 2 inskickade artiklar, som visas inte nu.
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Sinigardi, Stefano <1985>. "Laser driven proton acceleration and beam shaping". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6230/.
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In the race to obtain protons with higher energies, using more compact systems at the same time, laser-driven plasma accelerators are becoming an interesting possibility. But for now, only beams with extremely broad energy spectra and high divergence have been produced.
The driving line of this PhD thesis was the study and design of a compact system to extract a high quality beam out of the initial bunch of protons produced by the interaction of a laser pulse with a thin solid target, using experimentally reliable technologies in order to be able to test such a system as soon as possible.
In this thesis, different transport lines are analyzed. The first is based on a high field pulsed solenoid, some collimators and, for perfect filtering and post-acceleration, a high field high frequency compact linear accelerator, originally designed to accelerate a 30 MeV beam extracted from a cyclotron.
The second one is based on a quadruplet of permanent magnetic quadrupoles: thanks to its greater simplicity and reliability, it has great interest for experiments, but the effectiveness is lower than the one based on the solenoid; in fact, the final beam intensity drops by an order of magnitude.
An additional sensible decrease in intensity is verified in the third case, where the energy selection is achieved using a chicane, because of its very low efficiency for off-axis protons.
The proposed schemes have all been analyzed with 3D simulations and all the significant results are presented. Future experimental work based on the outcome of this thesis can be planned and is being discussed now.
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Ratsibi, Humbelani Edzani. "Laser drilling of metals and glass using zero-order bessel beams". University of the Western Cape, 2013. http://hdl.handle.net/11394/5428.
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>Magister Scientiae - MScThis dissertation consists of two main sections. The first section focuses on generating zero order Bessel beams using axicons. An axicon with an opening angle y = 5⁰ was illuminated with a Gaussian beam of width ω₀ = 1.67 mm from a cw fiber laser with central wavelength λ = 1064 nm to generate zero order Bessel beams with a central spot radius r₀ = 8.3 ± 0.3 μm and propagation distance ½zmax = 20.1 ± 0.5 mm. The central spot size of a Bessel beam changes slightly along the propagation distance. The central spot radius r₀ can be varied by changing the opening angle of the axicon, y, and the wavelength of the beam. The second section focuses on applications of the generated Bessel beams in laser microdrilling. A Ti:Sapphire pulsed femtosecond laser (λ = 775 nm, ω₀ = 2.5 mm, repetition rate kHz, pulse energy mJ, and pulse duration fs) was used to generate the Bessel beams for drilling stainless steel thin sheets of thickness 50 μm and 100 μm and microscopic glass slides 1 mm thick. The central spot radius was r₀ = 15.9 ± 0.3 μm and ½zmax = 65.0 ± 0.5 mm. The effect of the Bessel beam shape on the quality of the holes was analysed and the results were discussed. It was observed that Bessel beams drill holes of better quality on transparent microscopic glass slides than on stainless steel sheet. The holes drilled on stainless steel sheets deviated from being circular on both the top and bottom surface for both thicknesses. However the holes maintained the same shape on both sides of each sample, indicating that the walls are close to being parallel. The holes drilled on the glass slides were circular and their diameters could be measured. The measured diameter (15.4±0.3 μm) of the hole is smaller than the diameter of the central spot (28.2 ± 0.1 μm) of the Bessel beam. Increasing the pulse energy increased the diameter of the drilled hole to a value close to the measured diameter of the central spot.
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Rafayelyan, Mushegh. "Singular beam shaping from spin-orbit flat optics". Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0583/document.
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Dans ce travail nous avons résolu deux problèmes principaux de la mise en forme topologique de faisceau paraxial pour les composants plans : la modalité et le polychromatisme.Nous les résolvons en introduisant de nouveaux concepts d’éléments optiques à interaction spin orbite,à savoir la “q-plate modale” et la “q-plate Bragg-Berry”. D’un côté, la q-plate modale convertit un faisceau gaussien incident en un faisceau de Laguerre-Gauss pour un indice radial et un indice d’azimut donnés, ce qui par conséquent dépasse les capacités des q-plates conventionnelles qui ne modifient que le degré de liberté azimutal, c.à.d. le moment orbital angulaire de la lumière. À des fins expérimentales, deux approches ont été développées : une basée sur des lames de verres nanostructurées artificiellement, l’autre sur des défauts topologiques de cristaux liquides auto-organisés naturellement. D’un autre côté, la q-plate Bragg-Berry consiste en une fine couche inhomogène de cristaux liquides chiraux (cholestériques) devant un miroir, ce qui fournit une mise en forme de faisceau spin-orbite pleinement efficace sur une large bande spectrale du faisceau incident, contrairement au q-plates conventionnelles qui ne sont fabriqués que pour une longueur d’onde donnée. Par ailleurs, nous obtenons une mise en forme de faisceau spin-orbite ultra-large bande en induisant une modulation de la structure supramoléculaire torsadée des cristaux liquides cholestériques selon la direction de propagation de la lumière. Nous montrons également que la présence du miroir derrière permet un puissant contrôle spatio-temporel des propriétés vectorielles de la polarisation du champ lumineux générées par la q-plate Bragg-BerryIt is well-known that paraxial coherent electromagnetic fields can be completelycharacterized in terms of their radial and azimuthal spatial degrees of freedom in the transverse planethat add to the polarization degree of freedom and wavelength. In this work we address two mainissues of paraxial beam shaping that are the modality and the polychromaticity in the context of flatopticsthat we address by introducing novel concepts of spin-orbit optical elements. Namely, the‘modal q-plate’ and the ‘Bragg-Berry q-plate’. On the one hand, modal q-plate converts an incidentfundamental Gaussian beam into a Laguerre-Gaussian beam of given radial and azimuthal indices,hence going beyond the capabilities of conventional q-plates that only control the azimuthal degreeof freedom, i.e. the orbital angular momentum content of light. Towards experimental realization ofmodal q-plates, two approaches are developed: one based on artificially nanostructured glasses andanother based on naturally self-organized liquid crystal topological defects. On the other hand,Bragg-Berry q-plate consist of mirror-backed inhomogeneous thin film of chiral liquid crystal(cholesteric) that provides fully efficient spin-orbit beam shaping over broad spectral range of theincident beam, in contrast to the conventional q-plates that are designed for single wavelength.Furthermore, ultra-broadband spin-orbit beam shaping is achieved by inducing an extra modulationof the supramolecular twisted structure of the cholesteric liquid crystal along the propagationdirection. We also show that the presence of a back-mirror allows a powerful spatio-temporal controlof the polarization vectorial properties of the light fields generated by Bragg-Berry q-plate
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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.
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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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Yang, Zhengyi. "Optical and acoustic beam shaping for imaging and manipulation". Thesis, University of Dundee, 2014. https://discovery.dundee.ac.uk/en/studentTheses/18d650a0-53ba-4f4d-9d61-78c3a6b68bf6.
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Sound and light show many similarities because they both propagate as waves. This means they share the same wave properties such as reflection, refraction, scattering, diffraction, and so on. The similarities between them bring a lot of opportunities for translating knowledge of one onto the other. When compared to ultrasound, and particularly in microscopy and micromanipulation, optics is a more-developed and better-understood area, partly due to the difficulty of producing complex ultrasonic beams. Hence it makes perfect sense to explore sound based on the research of optics. Differences between light and sound are mainly due to the nature variety of their mechanisms and different scale of their wavelength. Those difference makes either light or sound suitable for certain applications. This thesis will focus on the currently technology for beam shaping for acoustic and optical waves, making use of their similarities, especially for imaging and manipulation purposes. When light scattering and absorption is low, optical scattering is able to provide high resolution and suitable for imaging. A low-cost Light-Sheet Tomography imaging system is built for monitoring the growth of plant roots based on optical scattering from the roots. When optical scattering and absorption is severe it dramatically decreases spatial resolution, optical absorption can be employed to generate less-scattered acoustic signals to form high contrast images of the optical absorbing structure in a sample. A photoacoustic imaging system featuring light sheet illumination is built, along with an automatic data acquisition system. 2D images acquired with this system are reconstructed with inverse Radon transformation. The short wavelength of optical waves makes them suitable for interaction with micron-scale objects, but less suitable for macro objects because the force does not easily scale up with the size of the targets. On the other hand, ultrasonic waves have the suitable wavelength and power level for interaction with mm- or even cm- size objects. Various ultrasonic beams with vortex wavefront were generated with a 1000-element phase-control transducer array to levitate and rotate a macro acoustic absorber by transferring linear and angular momentum from the acoustic beam to the absorber. The ratio between linear and angular momentum in the beam was measured simultaneously. With the same ultrasound transducer array, the delivery of a controllable negative radiation force onto prism-shape target is demonstrated to pull the prism towards the sound source. This is the first demonstration of macroscopic and ultrasonic tractor beam. The study of ultrasound and optical beam shaping has proven that the similarities between sound and light waves can be utilized to extend our existing knowledge on them, and further provides more opportunities on wave-matter interaction applications.
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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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Victor, Brian M. "Custom Beam Shaping for High-Power Fiber Laser Welding". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1238014676.
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Zhang, Shuyan. "Spatial beam shaping of high-power ultrashort laser pulses". W&M ScholarWorks, 2007. https://scholarworks.wm.edu/etd/1539623522.
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This thesis presents both theoretical and experimental studies of a diffractive beam shaping system for ultrashort high-power laser pulses.;A theoretical model is developed to simulate the reshaped intensity profiles for a 100-fs pulse with various energy levels. Both temporal evolution and spatial intensity distribution of the pulse at the target plane of the beam shaping system are calculated. Numerical simulation shows that after passing through the beam shaping system, the pulse front is significantly curved due to the propagation time delay, and the pulse duration time through the target plane is broadened because of the group velocity dispersion. However, for relatively low energy pulses (on the order of millijoules), although the intensity distribution is changed considerably, the fluence top-hat profile is well maintained. This feature extends the application of this beam shaping system into the regime of ultrashort laser pulses. Theoretical calculation also shows the limit when the top-hat profile starts to degrade. For very high-energy laser pulses (>20 mJ per pulse), the homogeneous fluence profile, as well as the intensity distribution, is destroyed due to the non-linear self phase modulation.;This thesis also presents an experimental study of the beam shaping system for ultrashort high-power laser pulses. A terawatt CPA laser amplification system was built in order to verify the theoretical simulation in experiment. The laser amplification system adopts a multi-pass configuration. The output of this CPA amplifier is operating at 30 Hz repetition rate with a pulse energy of 20 mJ/pulse. The compressed pulse duration is 70 fs, resulting in a pulse peak power of 0.3 TW. Experimental results of the beam shaping system with ultrashort laser pulse input agree with the numerical simulation of the reshaped fluence profiles at various energy levels from 6nJ to 20 mJ. The experimental results confirm the validity of this diffractive beam shaping system for ultrashort pulses with a pulse energy on the order of millijoulses. While millijoule pulses are commonly used in the micromachining technology, the adaptability of this diffractive beam shaping system is greatly improved.
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Holdsworth, Adrian Richard. "Brightness conserving optical systems for high power diode lasers". Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/583.
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Wellburn, Daniel. "Circular laser beam intensity profile shaping for uniform surface treatments". Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533912.
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Cheng, Wen. "Optical Vortex Beams: Generation, Propagation and Applications". University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1375370902.
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Ament, Craig A. "High numerical aperture axial and transverse beam shaping using diffractive optics". Honors in the Major Thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1348.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Sciences
Physics
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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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Du, Plessis Anton. "A characterization of beam shaping devices and a tunable Raman laser". Thesis, Stellenbosch : University of Stellenbosch, 2003. http://hdl.handle.net/10019.1/16313.
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Thesis (MSc)--University of Stellenbosch, 2003.ENGLISH ABSTRACT: The efficient manipulation of various nonlinear optical processes frequently requires the shaping of the laser beams used for these processes. Three beam shaping techniques were investigated in this thesis. The focussing of Gaussian laser beams was investigated analytically, in order to efficiently manipulate the focussed beam characteristics. The beam-shaping characteristics of a diffractive optical element (DOE) was investigated numerically, which illustrates the beamshaping capability of the DOE, and identifies the critical parameters in experimental situations. The use of a waveguide as beam shaping device was investigated analytically and experimentally, and characterized for use with the available tunable laser sources. A Raman laser, or Raman shifter, employs stimulated vibrational Raman scattering to generate laser radiation at shifted frequencies. The waveguide was successfully applied as a beam shaping device in the Raman laser system, for optimisation of the process. The Raman laser system was investigated experimentally and characterized for use with the available tunable laser sources. The successful generation of laser radiation at shifted frequencies illustrates the usefulness of the system for generating tunable red-shifted frequencies. The results of this work allow the simple and efficient application of the Raman laser to generate laser radiation at shifted frequencies, in particular tunable infrared laser radiation which is desirable for molecular spectroscopy.
AFRIKAANSE OPSOMMING: Nie-liniêre optiese prosesse kan meer effektief benut word deur die vervorming van die laserbundels wat gebruik word in die prosesse. In hierdie tesis word drie laserbundel-vervormings tegnieke ondersoek. Die fokussering van Gaussiese laserbundels word analities ondersoek, om die gefokusseerde bundel se eienskappe effektief te manipuleer. Die bundel-vervormings eienskappe van ’n diffraktiewe optiese element word numeries ondersoek, wat die effektiwiteit van die bundelvervorming en die sensitiewe parameters in die sisteem uitwys. Die gebruik van ’n golfgeleier as ’n bundel-vervormings tegniek word ook analities en eksperimenteel ondersoek, en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare laser sisteme. ’n Raman laser, wat gestimuleerde vibrasionele Raman verstrooiing gebruik om laser lig te genereer by Stokes-verskuifde frekwensies, word ondersoek. Die golfgeleier word effektief gebruik as ’n bundel-vervormings tegniek in die Raman laser, om die bogenoemde nie-liniêre proses te optimeer. Die Raman laser was eksperimenteel ondersoek en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare lasers. Laser lig by verskuifde golflengtes is suksesvol gegenereer, wat die bruikbaarheid van die sisteem illustreer. Van belang is spesifiek verstelbare infrarooi laser lig, wat gebruik kan word in die laser-spektroskopie van molekules. Die resultate van hierdie werk lei tot die eenvoudige en effektiewe gebruik van die Raman laser, om langer golflengtes in die infrarooi gebied te genereer met ’n gegewe laser in die sigbare gebied.
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Penner, Robert Scott. "Focusing, wavelength tuning, beam steering and beam shaping of circular grating surface emitting distributed Bragg reflector lasers". Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284042.
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Over the past decade, circular grating surface emitting DBR lasers (CGSELs) have progressed from theory to reality. These devices possess several properties that make them attractive options for such applications as optical interconnects and laser arrays. These advantages include low divergence angles, circular beam profiles, and high power output. In this dissertation, the addition of new functionality to these lasers including wavelength tunability, focusing, beam steering and beam shaping is investigated. The theory governing device operation is presented. Pertinent discussions include the coupled mode equations, grating coupling, focusing and changes to the effective index of refraction resulting from current injection through a transparent electrode on the grating. The development and refinement of the device fabrication process is detailed. Key milestones in the grating writing process included achieving first order gratings (Λ = 0.15 μm), creating chirped period gratings for focusing and optimizing the linewidth and uniformity of the grating for high power devices. Of equal importance in obtaining high efficiency devices was the reactive ion etch process. Two different etch recipes were developed: one for mesa-definition and a shallower grating-defining etch. Significant evaluation of the electrical and optical properties of the transparent electrode, Indium Tin Oxide, was performed. Incorporating ITO into the fabrication process required optimization of deposition, patterning, etching and annealing. Device performance, efficiency and functionality improved with each generation. Consequentially, over 225 mW of output power for a injection current of 600 mA, or a slope efficiency of 0.43 mW/mA, was produced by the final generation of high power CGSELs. Focusing was demonstrated by the creation of individual devices with different focal lengths. Coarse mode selection was obtained by removing radial segments of the circular grating thereby eliminating both feedback coupling and surface outcoupling. Dynamic functionality such as beam steering and wavelength tuning was also realized for devices with ITO. Over 1° of beam steering was achieved for an ITO injection current of 35 mA. Similarly, over 1 nm of tuning, or 0.5 nm of continuous tuning, was accomplished. In conclusion, possibilities for improvements in device performance and future work are suggested.
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Burnham, Daniel Richard. "Microscopic applications of holographic beam shaping and studies of optically trapped aerosols /". St Andrews, 2009. http://hdl.handle.net/10023/699.
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Stefansson, Gudmundur, Suvrath Mahadevan, Leslie Hebb, John Wisniewski, Joseph Huehnerhoff, Brett Morris, Sam Halverson i in. "Toward Space-like Photometric Precision from the Ground with Beam-shaping Diffusers". IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626043.
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We demonstrate a path to hitherto unachievable differential photometric precisions from the ground, both in the optical and near-infrared (NIR), using custom-fabricated beam-shaping diffusers produced using specialized nanofabrication techniques. Such diffusers mold the focal plane image of a star into a broad and stable top-hat shape, minimizing photometric errors due to non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and telescope-induced variable aberrations seen in defocusing. This PSF reshaping significantly increases the achievable dynamic range of our observations, increasing our observing efficiency and thus better averages over scintillation. Diffusers work in both collimated and converging beams. We present diffuser-assisted optical observations demonstrating 62(-16)(+26) ppm precision in 30 minute bins on a nearby bright star 16 Cygni A (V = 5.95) using the ARC 3.5 m telescope-within a factor of similar to 2 of Kepler's photometric precision on the same star. We also show a transit of WASP-85-Ab (V = 11.2) and TRES-3b (V = 12.4), where the residuals bin down to 180(-41)(+66) ppm in 30 minute bins for WASP-85-Ab-a factor of similar to 4 of the precision achieved by the K2 mission on this target-and to 101 ppm for TRES-3b. In the NIR, where diffusers may provide even more significant improvements over the current state of the art, our preliminary tests demonstrated 137(-36)(+64) ppm precision for a K-S = 10.8 star on the 200 inch. Hale Telescope. These photometric precisions match or surpass the expected photometric precisions of TESS for the same magnitude range. This technology is inexpensive, scalable, easily adaptable, and can have an important and immediate impact on the observations of transits and secondary eclipses of exoplanets.
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Burnham, Daniel R. "Microscopic applications of holographic beam shaping and studies of optically trapped aerosols". Thesis, University of St Andrews, 2009. http://hdl.handle.net/10023/699.
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This thesis has two themes. Firstly, it concerns the original application of holographic beam shaping, employed through the methods associated with optical manipulation, to three microscopic fields of research. Secondly, it studies the optical trapping of aerosol droplets through experimentation and computational modelling. The aims are to not only provide an account of the work carried out but also a base for future researchers and students. Chapter 1 provides an introduction to the field of optical manipulation and the relevance of my studies. Chapter 2 outlines the construction of an optical tweezers which is the basis of advanced experimental work described in later chapters. It also overviews how optical tweezers operate and are quantified. In chapter 3 I describe how beam shaping is implemented for my investigations with a spatial light modulator and phase-only holograms. I detail the algorithms and software written before discussing their performance and finally the optimisation of the apparatus. Chapter 4 describes three original applications of beam shaping, including the trapping and coagulation of multiple aerosols, the manipulation of filamentous fungi hyphal tips and novel digital microfluidic operations using thermocapillary forces. I also lay down preliminary results for observing orbital angular acceleration using beams carrying orbital angular momentum. To study single optically trapped aerosols I use two methods. Firstly, their Brownian motion is investigated through sub diffraction limit position detection. Unique results in optical tweezers are shown with liquid droplets behaving as under-damped Brownian oscillators. Through these studies I demonstrate a new technique for sizing trapped aerosols, with significant advantages over current methods. I also show that the droplets can be be parametrically excited which can result in trap failure. Secondly, in chapter 6, I use a theoretical model to describe the forces imparted to a trapped droplet. I extend current theories to include the effects of a three medium focal region to accurately describe airborne optical traps. The work qualitatively explains the phenomena observed experimentally. The work contained here leaves much scope for future investigations, for which I provide an overview in chapter 7.
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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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Zhang, Chong. "THERMAL MODELING AND LASER BEAM SHAPING FOR MICROVIAS DRILLING IN HIGH DENSITY PACKAGING". Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2255.
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Laser drilling of microvias for organic packaging applications is studied in present research. Thermal model is essential to understand the laser-materials interactions and to control laser drilling of blind micro holes through polymeric dielectrics in multilayer electronic substrates. In order to understand the profile of the drilling front irradiated with different laser beam profiles, a transient heat conduction model including vaporization parameters is constructed. The absorption length in the dielectric is also considered in this model. Therefore, the volumetric heating source criteria are applied in the model and the equations are solved analytically. The microvia drilling speed, temperature distribution in the dielectric and the thickness of the residue along the microvia walls and at the bottom of the microvia are studied for different laser irradiation conditions. An overheated metastable state of material is found to exist inside the workpiece. The overheating parameters are calculated for various laser drilling parameters and are used to predict the onset of thermal damage and to minimize the residue. As soon as a small cavity is formed during the drilling process, the concave curvature of the drilling front acts as a concave lens that diverges the incident laser beam. This self-defocusing effect can greatly reduce the drilling speed. This effect makes the refractive index of the substrate at different wavelengths an important parameter for laser drilling. A numerical thermal model is built to study the effect of self-defocusing for laser microvias drilling in multilayer electronic substrates with Nd:YAG and CO2 lasers.. The laser ablation thresholds was calculated with this model for the CO2 and Nd:YAG lasers respectively. Due to the expulsion of materials because of high internal pressures in the case of Nd:YAG laser microvia drilling, the ablation threshold may be far below the calculated value. A particular laser beam shape, such as pitch fork, was found to drill better holes than the Gaussian beam in terms of residue and tapering angle. Laser beam shaping technique is used to produce the desired pitchfork beam. Laser beam shaping allows redistribution of laser power and phase across the cross-section of the beam for drilling perfectly cylindrical holes. An optical system, which is comprised of three lenses, is designed to transform a Gaussian beam into a pitchfork beam. The first two lenses are the phase elements through which a Gaussian laser beam is transformed into a super Gaussian beam. The ray tracing technique of geometrical optics is used to design these phase elements. The third lens is the transform element which produces a pitchfork profile at the focal plane due to the diffraction effect. A pinhole scanning power meter is used to measure the laser beam profile at the focal plane to verify the existence of the pitchfork beam. To account for diffraction effect, the above mentioned laser beam shaping system was optimized by iterative method using Adaptive Additive algorithm. Fresnel diffraction is used in the iterative calculation. The optimization was target to reduce the energy contained in the first order diffraction ring and to increase the depth of focus for the system. Two diffractive optical elements were designed. The result of the optimization was found dependent on the relation between the diameter of the designed beam shape and the airy disk diameter. If the diameter of the designed beam is larger, the optimization can generate better result. Drilling experiment is performed with a Q-switched CO2 laser at wavelength of 9.3 μm. Comparison among the drilling results from Gaussian beam, Bessel beam and Pitchfork beam shows that the pitchfork beam can produce microvias with less tapering angle and less residue at the bottom of the via. Laser parameters were evaluated experimentally to study their influences on the via quality. Laser drilling process was optimized based on the evaluation to give high quality of the via and high throughput rate. Nd:YAG laser at wavelengths of 1.06 μm and 532 nm were also used in this research to do microvias drilling. Experimental result is compared with the model. Experimental results show the formation of convex surfaces during laser irradiation. These surfaces eventually rupture and the material is removed explosively due to high internal pressures. Due to the short wavelength, high power, high efficiency and high repetition rate, these lasers exhibit large potentials for microvias drilling.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering PhD
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Han, Jiho. "Phase modulated fibre amplifier array for high power real-time arbitrary beam shaping". Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267906.
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McDonald, Craig. "Applications of optical manipulation for low cost implementation, beam shaping and biophysical force measurements". Thesis, University of Dundee, 2017. https://discovery.dundee.ac.uk/en/studentTheses/35080e80-77ec-4442-826c-cab158e524fd.
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There are a growing variety of research fields requiring non-contact micro- manipulation. An increasing number of these fields are turning to optical tweezers as a solution, owing to their high spatial and temporal resolution. Optical tweezers have the ability to quantitively exert and measure forces on the piconewton scale, a convenient force scale for soft biological materials, and are hugely versatile due to the wide assortment of beam shaping techniques that can be employed. The work in this thesis can be broadly divided into two main themes: that quantifying the optical trapping forces in shaped beams; and bringing control and simplification of complex systems to non-expert users who may utilise optical tweezers as part of interdisciplinary collaborations. Static beam shaping is used to generate a conically refracted optical trap and the trapping properties are characterised. It is shown that trapping in the lower Raman spot gives full, 3D gradient trapping, while the upper Raman spot allows for particle guiding due to its levitation properties. Particles in the Lloyd/Poggendorff rings experience a lower trap stiffness than particles in the lower Raman spot but benefit from rotational control. Dynamic beam shaping techniques are exploited for the simplification of complex systems through the development and testing of the HoloHands program. This software allows a holographic optical tweezers experiment to be controlled by gestures that are detected by a Microsoft Kinect. Multiple particle manipulation is demonstrated, as well as a calibration of the tweezers system. Application of trapping forces is demonstrated through an examination of integrin – ligand bond strength. Both wild type effector T cells and those with a kindlin-3 binding site mutation similar to that found in neutrophils from Leukocyte Adhesion Deficiency sufferers are investigated. Through the use of back focal plane interferometry, a bond rupture force of (17.9 ± 0.6) pN at a force loading rate of (30 ± 4) pN/s, was measured for single integrins expressed on wild type cells. As expected, a significant drop in rupture force of bonds was found for mutated cells, with a measured rupture force of (10.1 ± 0.9) pN at the same pulling rate. Therefore, kindlin-3 binding to the cytoplasmic tail of the β2-tail directly affects bond strength of single integrin-ligand bonds. An experimental system for studying these cells under more physiologically relevant conditions is also presented. Additionally, a low-cost optical micromanipulation system that makes use of simple microfabricated components coupled to a smartphone camera for imaging is proposed and demonstrated. Through the layering of hanging droplets of polydimethylsiloxane (PDMS) on microscope coverslips, lenses capable of optical trapping are created. Combination of PDMS with Sudan II dye led to the fabrication of long pass filters. An extension of this low-cost system into the life sciences is proposed through the adaptive use of bubble wrap, which allows for the culturing of cells in a chamber compatible with optical trapping.
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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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Kong, Fanqi. "High-Order Harmonic Generation with Structured Beams". Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39609.
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The generation of high-order harmonics opened an era of attosecond science wherein coherent light bursts are used to probe dynamic processes in matter with a time resolution short enough to resolve the motions of electrons. It enabled the development of extreme ultraviolet (XUV) and X-ray table-top sources with both temporal and spatial coherence, which provides the ability to shape the temporal and spatial structure of the XUV pulses.
Scientists developed techniques to control and measure the temporal structure high harmonic emissions. These techniques exploited control of the driving laser pulse in the time domain and facilitated development of more advanced high-harmonic based XUV sources that have greatly impacted ultrafast measurements.
In this thesis, I apply techniques to control and measure the spatial structure of high harmonic emissions, and discuss the underlying physics and potential applications of the interaction between spatially structured laser beams and materials. This study exploits the spatial degree of freedom in strong field interaction, which has not been given as much attention as the temporal degree of freedom.
I use liquid crystal devices to shape the wave front of a fundamental laser beam to a vortex structure, then imprint this structured wave front onto XUV beams through high harmonic generation. This method provides an alternative to special XUV optics, which can manipulate the wave front of XUV radiation by all optical means. This result also reveals the conservation of orbital angular momentum in this extreme nonlinear wave mixing process. In addition to shaping the wave front, shaping the polarization of the driving beam also allows generation of circularly polarized the XUV radiation using a high harmonic source.
This thesis also highlights the interplay between shaping the wave front and polarization in the high harmonic generation process. The topology of the structured beam can be maintained through this extreme nonlinear interaction due to the spin selection rules and spin-orbit conservation.
Moreover, this thesis demonstrates an approach to integrate a vector beam into a broadband ultrafast light source and overcome the bandwidth limitation of mode converters. We use this approach to generate a few-cycle structured beam. In the future, this beam will be used to generate a strong ultrafast magnetic impulse in gas and solid targets by driving currents in a loop, which is a valuable tool for the future of magnetic metrology.
The novel properties of structured laser beams discussed in this thesis expanded the capabilities of high harmonic based XUV sources and have opened a new field to explore this additional degree of freedom in strong field interactions.
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Namarathne, Dinithi L. "Measuring intensity dependent optical nonlineartities without sample damage using higher order vortex beams". Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/129569/9/Dinithi_Namarathne_Thesis.pdf.
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This study developed a beam shaping based method to avoid nonlinear sample damage in high intense pulse laser applications. This is achieved by developing a complete theoretical and experimental framework for Z-scan experiments to utilise higher order vortex beams instead of common Gaussian beam. An image processing based extension was introduced to Z-scan experiments, which can be utilised to achieve results of different Z-scan modes from a single experimental dataset efficiently. The results of this study will have a positive impact on utilising different beam profiles to achieve profile specific advantages in nonlinear applications.
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Barcík, Peter. "Rozložení relativní variance optické intenzity ve svazcích". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219880.
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This master´s thesis provides basic properties and measurement of optical beams. In the first chapter is shown division of light on ray, wave and beam optics. Atmospheric optics and properties associated with propagation of light through the earth's atmosphere is presented in the second chapter. In the third part are shown basic techniques for Gaussian beam shaping. The last chapter deals with measurement of optical beam after propagating through a turbulent medium. In this section is shown distribution of relative variance of optical intensity in Gaussian and Top-Hat beam. There is also measured spatial coherence of laser beam in the turbulent atmospheric transmission media. Finally effect of the beam wander is investigated.
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Jiang, Miao. "DESIGNS AND APPLICATIONS OF PLASMONIC METAMASKS FOR TOPOLOGICAL DEFECT ENGINEERING AND MANUFACTURING OF PANCHARATNAM FLAT OPTICAL ELEMENTS". Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1533742796947775.
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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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Chung, Te-yuan. "THERMAL MANAGEMENT, BEAM CONTROL,AND PACKAGING DESIGNS FOR HIGH POWER". Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3879.
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Several novel techniques for controlling, managing and utilizing high power diode lasers are described. Low pressure water spray cooling for a high heat flux system is developed and proven to be an ideal cooling method for high power diode laser arrays. In order to enable better thermal and optical performance of diode laser arrays, a new and simple optical element, the beam control prism, is invented. It provides the ability to accomplish beam shaping and beam tilting at the same time. Several low thermal resistance diode packaging designs using beam control prisms are proposed, studied and produced. Two pump cavity designs using a diode laser array to uniformly pump rod shape gain media are also investigated.Ph.D.
Other
Optics and Photonics
Optics
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Serkan, Mert Kirkici Hulya. "Laser beam shaping optical system design methods and their application in edge-emitting semiconductor laser-based lidar systems". Auburn, Ala., 2007. http://repo.lib.auburn.edu/2007%20Fall%20Dissertations/Serkan_Mert_22.pdf.
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Baig, Sarfaraz Niaz Ali. "Soft Lithographic Fabrication of Micro Optics and Integrated Photonic Components". Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_theses/179.
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Optical waveguides, quantum dot emitters, and flat top beam shapers were designed and fabricated by two soft lithographic techniques; micro transfer molding (microTM) and vacuum assisted microfluidics (VAM). Optical waveguides were fabricated through a microTM technique that utilizes a poly dimethylsiloxane (PDMS) stamp. Generation of the flexible stamp required development of a channel waveguide pattern mask, defined by maskless lithography, and followed by construction of a three dimensional channel waveguide master, acquired through contact lithography on a glass substrate coated with SU-8 photoresist. Creation of a positive imprint replicating mold was accomplished through prepolymer PDMS solution settling and curing around the master. Waveguide fabrication was achieved through PDMS conformal contact on, and subsequent curing of, ultraviolet (UV) polymer resins on a silicon substrate. A slight modification of the microTM PDMS stamp, whereby inlet and outlet tunnels were incorporated, resulted in a novel VAM structure and correspondingly waveguides. Waveguide propagation losses were determined to be 1.14 dB/cm and 0.68 dB/cm for the microTM and VAM fabricated waveguides, respectively. A lithographic approach employing quantum dots doped in SU-8 photoresist has led to the realization of a new quantum dot emitter. Uniform coating of a doped material on a silver coated substrate was followed by contact mask lithography. Evaporation of a thin silver layer, upon development of the resultant quantum dot doped channel waveguide structure, facilitates confined emission. Successful edge emitting was demonstrated with blue laser pumping. The lithographic fabrication of such quantum dot emitter is successfully replaced by soft lithographic VAM technique. A flat top beam shaper, whose profile was developed on cured UV polymer resins, was fabricated by microTM technique. The master used for the development of the PDMS stamp was produced through an iterative wet etching process capable of achieving etching depths as small as a few nanometers. Comparisons between the reference wet etched beam shaper and the microTM based beam shaper produced near identical output flat top beams from incident Gaussian beams. Through this research work, successful soft lithographic fabrication of optical waveguides, quantum dot emitters, and flat top beam shapers were demonstrated. The vast potential exhibited by these and other related technologies show great promise for cost-effective mass production of various micro optics and integrated photonic components.
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Yi, Fan, i n/a. "Optimal Algorithmic Techniques of LASIK Procedures". Griffith University. School of Engineering, 2006. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20070216.152339.
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Clinical wavefront-guided corneal ablation has been now the most technologically advanced method to reduce the dependence of glasses and contact lenses. It has the potential not only to eliminate spherocylindrical errors but also to reduce higher-order aberrations (HOA). Recent statistics show that more than 96% of the patients who received laser in situ keratomileusis (LASIK) treatment reported their satisfaction about the improvement on vision, six months after the surgery. However, there are still patients complaining that their vision performance did not achieve the expectation or was even worse than before surgery. The reasons causing the unexpected post-surgical outcome include undercorrection, overcorrection, induced HOA, and other postoperative diseases, most of which are caused by inaccurate ablation besides other pathological factors. Therefore, to find out the method to optimize the LASIK procedures and provide a higher surgical precision has become increasingly important. A proper method to calculate ablation profile and an effective way to control the laser beam size and shape are key aspects in this research to resolve the problem. Here in this Master of Philosophy degree thesis, the author has performed a meticulous study on the existing methods of ablation profile calculation and investigated the efficiency of wavefront only ablation by a computer simulation applying real patient data. Finally, the concept of a refractive surgery system with dynamical beam shaping function is sketched, which can theoretically overcome the disadvantages of traditional procedures with a finite laser beam size.
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Yi, Fan. "Optimal Algorithmic Techniques of LASIK Procedures". Thesis, Griffith University, 2006. http://hdl.handle.net/10072/368097.
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Clinical wavefront-guided corneal ablation has been now the most technologically advanced method to reduce the dependence of glasses and contact lenses. It has the potential not only to eliminate spherocylindrical errors but also to reduce higher-order aberrations (HOA). Recent statistics show that more than 96% of the patients who received laser in situ keratomileusis (LASIK) treatment reported their satisfaction about the improvement on vision, six months after the surgery. However, there are still patients complaining that their vision performance did not achieve the expectation or was even worse than before surgery. The reasons causing the unexpected post-surgical outcome include undercorrection, overcorrection, induced HOA, and other postoperative diseases, most of which are caused by inaccurate ablation besides other pathological factors. Therefore, to find out the method to optimize the LASIK procedures and provide a higher surgical precision has become increasingly important. A proper method to calculate ablation profile and an effective way to control the laser beam size and shape are key aspects in this research to resolve the problem. Here in this Master of Philosophy degree thesis, the author has performed a meticulous study on the existing methods of ablation profile calculation and investigated the efficiency of wavefront only ablation by a computer simulation applying real patient data. Finally, the concept of a refractive surgery system with dynamical beam shaping function is sketched, which can theoretically overcome the disadvantages of traditional procedures with a finite laser beam size.Thesis (Masters)
Master of Philosophy (MPhil)
School of Engineering
Full Text
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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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Kropáč, Ondřej. "Návrh tvarovacího systému pro laserový svazek". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219163.
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Diploma thesis deal with design of laser beam shaping system. The theoretical part presents basic information about the light spread lika the optical beams. There are also properties of optical and optoelectronic components that are used for shaping the laser beam. The next section provides basic molding methods, their principles and qualities. In the last, experimental, part is first introduced designed computer algorithm, which is then used to calculate the quality parameters shaped laser beams. Following, there are presented the results of measurements and calculations for some of these methods.
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Fournier, Florian. "FREEFORM REFLECTOR DESIGN WITH EXTENDED SOURCES". Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3146.
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Reflector design stemmed from the need to shape the light emitted by candles or lamps. Over 2,000 years ago people realized that a mirror shaped as a parabola can concentrate light, and thus significantly boosts its intensity, to the point where objects can be set afire. Nowadays many applications require an accurate control of light, such as automotive headlights, streetlights, projection displays, and medical illuminators. In all cases light emitted from a light source can be shaped into a desired target distribution with a reflective surface. Design methods for systems with rotational and translational symmetry were devised in the 1930s. However, the freeform reflector shapes required to illuminate targets with no such symmetries proved to be much more challenging to design. Even when the source is assumed to be a point, the reflector shape is governed by a set of second-order partial non-linear differential equations that cannot be solved with standard numerical integration techniques. An iterative approach to solve the problem for a discrete target, known as the method of supporting ellipsoids, was recently proposed by Oliker. In this research we report several efficient implementations of the method of supporting ellipsoids, based on the point source approximation, and we propose new reflector design techniques that take into account the extent of the source. More specifically, this work has led to three major achievements. First, a thorough analysis of the method of supporting ellipsoids was performed that resulted in two alternative implementations of the algorithm, which enable a fast generation of freeform reflector shapes within the point source approximation. We tailored the algorithm in order to provide control over the parameters of interest to the designers, such as the reflector scale and geometry. Second, the shape generation algorithm was used to analyze how source flux can be mapped onto the target. We derived the condition under which a given source-target mapping can be achieved with a smooth continuous surface, referred as the integrability condition. We proposed a method to derive mappings that satisfy the integrability condition. We then use these mappings to quickly generate reflector shapes that create continuous target distributions as opposed to reflectors generated with the method of supporting ellipsoids that create discrete sets of points on the target. We also show how mappings that do not satisfy the integrability condition can be achieved by introducing step discontinuities in the reflector surface. Third, we investigated two methods to design reflectors with extended sources. The first method uses a compensation approach where the prescribed target distribution is adjusted iteratively. This method is effective for compact sources and systems with rotational or translational symmetry. The second method tiles the source images created by a reflector designed with the method of supporting ellipsoids and then blends the source images together using scattering in order to obtain a continuous target distribution. This latter method is effective for freeform reflectors and target distributions with no sharp variations. Finally, several case studies illustrate how these methods can be successfully applied to design reflectors for general illumination applications such as street lighting or luminaires. We show that the proposed design methods can ease the design of freeform reflectors and provide efficient, cost-effective solutions that avoid unnecessary energy consumption and light pollution.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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Mourka, Areti. "Probing the modal characteristics of novel beam shapes". Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/4287.
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In this thesis, an investigation into the modal characteristics of novel beam shapes is presented. Sculpting the phase profile of a Gaussian beam can result in the generation of a beam with unique properties. Described in this thesis are Laguerre-Gaussian (LG), Hermite-Gaussian (HG) and Bessel beams (BBs). The diffraction of LG beam modes from a triangular aperture is explored and this effect can be used for the efficient measurement of the azimuthal mode index l that indicates the number of multiples of 2π of phase changes that the field displays around one circumference of the optical axis. In this study, only LG beams with zero radial mode index p, with p + 1 denoting the number of bright high intensity concentric rings around the optical axis, were considered. Then, a powerful approach to simultaneously determine both mode indices of a pure LG beam using the principal component analysis (PCA) algorithm on the observed far-field diffraction patterns was demonstrated. Owing to PCA algorithm, the shape of the diffracting element used to measure the mode indices is in fact of little importance and the crucial step is ‘training' any diffracting optical system and transforming the observed far-field diffraction patterns into the uncorrelated variables (principal components). Our PCA method is generic and it was extended to other families of light fields such as HG, Bessel and superposed beams. This reinforces the widespread applicability of this method for various applications. Finally, both theoretically and experimentally investigations using interferometry show the definitive linkage between both the radial and azimuthal mode indices of a partially coherent LG beam and the dislocation rings in the far-field cross-correlation function (CCF).
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Jabbour, Toufic. "DESIGN, ANALYSIS, AND OPTIMIZATION OF DIFFRACTIVE OPTICAL ELEMENTS UNDER HIGH NUMERICAL APERTURE FOCUSING". Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2837.
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The demand for high optical resolution has brought researchers to explore the use of beam shaping diffractive optical elements (DOEs) for improving performance of high numerical aperture (NA) optical systems. DOEs can be designed to modulate the amplitude, phase and/or polarization of a laser beam such that it focuses into a targeted irradiance distribution, or point spread function (PSF). The focused PSF can be reshaped in both the transverse focal plane and along the optical axis. Optical lithography, microscopy and direct laser writing are but a few of the many applications in which a properly designed DOE can significantly improve optical performance of the system. Designing DOEs for use in high-NA applications is complicated by electric field depolarization that occurs with tight focusing. The linear polarization of off-axis rays is tilted upon refraction towards the focal point, generating additional transverse and longitudinal polarization components. These additional field components contribute significantly to the shape of the PSF under tight focusing and cannot be neglected as in scalar diffraction theory. The PSF can be modeled more rigorously using the electromagnetic diffraction integrals derived by Wolf, which account for the full vector character of the field. In this work, optimization algorithms based on vector diffraction theory were developed for designing DOEs that reshape the PSF of a 1.4-NA objective lens. The optimization techniques include simple exhaustive search, iterative optimization (Method of Generalized Projections), and evolutionary computation (Particle Swarm Optimization). DOE designs were obtained that can reshape either the transverse PSF or the irradiance distribution along the optical axis. In one example of transverse beam shaping, all polarization components were simultaneously reshaped so their vector addition generates a focused flat-top square irradiance pattern. Other designs were obtained that can be used to narrow the axial irradiance distribution, giving a focused beam that is superresolved relative to the diffraction limit. In addition to theory, experimental studies were undertaken that include (1) fabricating an axially superresolving DOE, (2) incorporating the DOE into the optical setup, (3) imaging the focused PSF, and (4) measuring aberrations in the objective lens to study how these affect performance of the DOE.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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BENKHEROUROU, SAHNOUNE SOURAYA. "Contribution a l'uniformisation du faisceau laser gaussien collimate par holographie numerique". Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13084.
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Presentation de deux techniques pour uniformiser le faisceau. La premiere est fondee sur le filtrage lineaire dans le domaine des frequences ou le faisceau est considere comme etant l'objet pouvant etre modifie par un filtre (hologramme) pour produire l'image filtree (faisceau uniforme). La seconde est constituee par deux filtres de phase. Le premier filtre sert a devier les rayons lumineux de facon a obtenir une repartition uniforme. Le second permet de collimater le faisceau deja uniformise par le premier
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CHEN, WEIBIN. "Focus Engineering with Spatially Variant Polarization for Nanometer Scale Applications". University of Dayton / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1259871061.
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Zhou, Sichao. "Complex Optical Fields Generation Using a Vectorial Optical Field Generator". University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1461689435.
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Hantl, Josef. "Tvarování laserového svazku". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219125.
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Thesis describes shortly types of waves and beams. Gaussian beam properties and parameters are described in more details, Gaussian beam is the most used in atmospheric optical links. The main goal of work is studying of possibilities of laser beam shaping, mainly the beam Top hat. In this project reasons why is suitable to shape laser beam for optical communications and the most used methods for shaping of laser beam are described. The suggested processes of beams shaping are experimentally verified and properties of beams shaped of single methods are compared with each other.
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Noori, Rahim Abadi Seyyed Mohammad Ali. "Investigation of Melt Pool Thermo-hydrodynamic Behaviour inLaser Beam Welding ofTi-6Al-4V through Numerical Simulation". Licentiate thesis, Högskolan Väst, Avdelningen för svetsteknologi (SV), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-17410.
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Laser is an efficient and widely used heat source in metal processing suchas welding and additive manufacturing. It has some great advantages compared to the other conventional heat sources like electron beam and arc namely: ability of handling complicated joint geometries and producing large components. Laser beam welding encompasses many complex physical phenomena such asheat transfer, metal melting, flow and solidification, free surface deformation, evaporation and possibly vaporization. The aim of this research work istwo-fold: gain deeper process understanding and improve the model reliability. Deeper process understanding is sought on the effect of beam shaping on themelt pool. To achieve improved model reliability, a good support consists in using qualitative experimental data representing the process. Thus, 3D validation of the melt pool geometry is performed while it was usually 2D inprevious research works. Furthermore, a new calculation procedure for laser absorption is introduced. To conduct this research work, a Computational Fluid Dynamics approach is used. A solver, capable of tracking the deformation of the melt free surface, is developed in OpenFOAM. Concerning beam shaping, it is found that not only the melt pool size as previously known but also the melt flow pattern is modified through elongating the beam shape.This last result could not be revealed by former studies as the non-transparent media hinders optical observation. New in-process quantitative measurements performed by a project partner are used to test the model. Weaknesses of the former absorptivity models are highlighted, as well as the limitations of the proposed model. Finally, the results show that the proposed absorptivity model function of local surface conditions leads to much better agreement with experimental results compared to the former constant absorptivity model. The maximum discrepancy compared to the experimental measurement, which is observed for the melt pool depth, can indeed be reduced to about 10%.Laser är en effektiv och allmänt använd värmekälla vid svetsning och additiv tillverkning. Den har några viktiga fördelar jämfört med andra konventionella värmekällor såsom elektronstråle och elektrisk ljusbåge, nämligen: den kan ofta användas till komplicerade svetsgeometrier, och den kan producera stora komponenter. Lasersvetsning involverar olika sammansatta fysikaliska fenomen såsom värmeöverföring, metallsmältning, flöde, stelning, ytdeformation, avdunstning och i vissa fall förångning. Syftet med mitt forskningsarbete är tvåfaldigt: att få en djupare processförståelse och att förbättra modellens tillförlitlighet. Fördjupad processförståelse eftersträvades för att förstå hur formen på laserstrålen påverkar svetssmältan. För att uppnå förbättrad modellsäkerhet behövs experimentella data av hög kvalitet som representerar processen. Således utfördes 3D-validering av smältgeometrin medan det vanligtvis var 2D i tidigare forskningsarbeten. Dessutom har en ny modell för laserabsorption föreslagits. I forskningen har numerisk strömningssimulering (Computational Fluid Dynamics) använts för att simulera processen och en numerisk lösare, som kan spåra deformationen av den rörliga smälta ytan, är utveckladi programvaran OpenFOAM. Beträffande laserstrålens utbredning visar resultaten att svetssmältans storlek och även svetssmältansflöde modifieras genom att laserstråleformen förlängs. Medan den förra är känd från tidigare experimentella studier upptäcktes den senare inte före denna studie eftersomdet icke-transparenta mediet hindrar optisk observation. Nya (in-process) kvantitativa mätningar utförda av en projektpartner har använts för att testa modellerna. Svagheter i den tidigare absorptionsmodellen framhävdes, liksom begränsningarna i den föreslagna modellen. Slutligen visade resultaten att den föreslagna modellen där laserabsorptionen är en funktion av lokala ytförhållanden ledde till en bättre overensstämmelse med mätningar jämfört med den tidigare modellen med konstant laserabsorbtion. Den maximala avvikelsen jämfört med experimentell mätning, som observerades med avseende på smältbassängsdjupet, kunde reduceras till cirka 10%.
Till licentiatuppsats hör 2 inskickade artiklar, som inte visas nu.
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Ouadghiri, Idrissi Ismail. "Nonlinear instabilities and filamentation of Bessel beams". Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCD071/document.
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Un faisceau de Bessel est un champ électromagnétique résistant à la diffraction. il peut se propager en préservant son profile transversal d'intensité même en régime de filamentation. Ceci est très avantageux pour les applications laser de haute puissance, en particulier parce qu’ils permettent de générer des canaux de plasma homogènes dans les diélectriques. Cependant, à haute intensité, les impulsions laser ultracourtes subissent, dans certaines conditions expérimentales (faible focalisation), des instabilités non linéaires entraînant la modulation d’intensité du lobe central au cours de la propagation, ce qui peut être néfaste pour ces applications comme l’usinage des matériaux transparents. L’objectif de cette thèse est de contrôler la génération de canaux de plasma par impulsions de Bessel via le contrôle du profil spatial de ces impulsions. Nous avons dans une première partie, développé une méthode expérimentale pour manipuler le profil d’intensité axiale en régime linéaire. La seconde partie concerne l’étude et le contrôle des instabilités non linéaires induites par l’effet Kerr. Nous avons développé un modèle théorique du mélange à quatre ondes dans les faisceaux de Bessel et avons démontré une nouvelle approche pour manipuler ces instabilités par une mise en forme appropriée de l’intensité axiale des faisceaux de Bessel. Nous avons ensuite étudié la validité des modèles de filamentation basés l’équation non linéaire de Schrödinger et le modèle de Drude. Les résultats expérimentaux de la filamentation des faisceaux de Bessel dans le verre ont montré un comportement invariant par propagation, contrairement aux modèles numériques. Nous avons testé et amendé les modèles de dynamiques de plasma et de propagation. Nos simulations sont comparées à des résultats expérimentaux. Nous montrons que les corrections que nous avons pu apporter par rapport à l’état de l’art sont insuffisantes et rendent nécessaire une autre forme de modèleBessel beams are solutions of Helmholtz equation. They can propagate while conserving their transverse intensity profile in space even in filamentation regime. This feature is very advantageous in high power laser applications such as plasma waveguide generation and laser ablation because they can generate homogeneous plasma channels in dielectrics. However, for moderate to low focusing conditions, Bessel pulses can sustain nonlinear instabilities, which consist in the modulation of the central core intensity along the propagation. Such a feature can prevent efficient energy deposition which hampers the applicability of Bessel pulses. The aim of this thesis is to investigate the possibility to control laser-generated plasma channels using spatially-reshaped Bessel pulses. In a first part, we have developed an experimental method based on a spatial light modulator to modify the evolution of the on-axis intensity of Bessel beams in the linear propagation regime. To study and control Kerr-induced instabilities, we developed, in a second part, a novel model based on four wave mixing interactions in Bessel beams. We have then demonstrated a novel approach to control these instabilities via on-axis intensity shaping. Bessel filamentation models in transparent media were then studied. Most models used in literature are based on nonlinear Schrödinger equation for light propagation and Drude model for laser-matter coupling. Experimental results on Bessel filamentation in glass showed propagation-invariant features in contrast with numerical simulations. Several corrections to this model were discussed. Our results show that such models are insufficient to explain our experimental results and thus the need to develop a more suitable one
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Hampl, Martin. "Prostorové dělení optických svazků". Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-233502.
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The dissertation thesis deals with a free space optical links, especially is focused directly to the transmission optical beams. The influence of environmental conditions like atmospheric turbulence, buildings movement and vibration is described. As a possibility to reduce these undesirable influences, the generation of the transmission beam by the help of the two-mode optical fiber is proposed. A possibility to drive the shape of the resulting transmission beam by means of the change of power ration of individual modes in fiber is described. The coherence features of the proposed beam are analyzed considering the possibility to reduce the influence of atmospheric turbulence. In the thesis there are introduced beam quality parameters that enable to evaluate the quality of the optical beam for the free space optical link. These parameters give the relationship between the shape of the optical beam and the power balance of the optical link and the statistical evaluation of the optical link.
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Chen, Sen-Yong. "Phonon Modulation by Polarized Lasers for Material Modification". Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5159.
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Magnetic resonance imaging (MRI) has become one of the premier non-invasive diagnostic tools, with around 60 million MRI scans applied each year. However, there is a risk of thermal injury due to radiofrequency (RF) induction heating of the tissue and implanted metallic device for the patients with the implanted metallic devices. Especially, MRI of the patients with implanted elongated devices such as pacemakers and deep brain stimulation systems is considered contraindicated. Many efforts, such as determining preferred MRI parameters, modifying magnetic field distribution, designing new structure and exploring new materials, have been made to reduce the induction heating. Improving the MRI-compatibility of implanted metallic devices by modifying the properties of the existing materials would be valuable. To evaluate the temperature rise due to RF induction heating on a metallic implant during MRI procedure, an electromagnetic model and thermal model are studied. The models consider the shape of RF magnetic pulses, interaction of RF pulses with metal plate, thermal conduction inside the metal and the convection at the interface between the metal and the surroundings. Transient temperature variation and effects of heat transfer coefficient, reflectivity and MRI settings on the temperature change are studied. Laser diffusion is applied to some titanium sheets for a preliminary study. An electromagnetic and thermal model is developed to choose the proper diffusant. Pt is the diffusant in this study. An electromagnetic model is also developed based on the principles of inverse problems to calculate the electromagnetic properties of the metals from the measured magnetic transmittance. This model is used to determine the reflectivity, dielectric constant and conductivity of treated and as-received Ti sheets. The treated Ti sheets show higher conductivity than the as-received Ti sheets, resulting higher reflectivity. A beam shaping lens system which is designed based on vector diffraction theory is used in laser diffusion. Designing beam shaping lens based on the vector diffraction theory offers improved irradiance profile and new applications such as polarized beam shaping because the polarization nature of laser beams is considered. Laser Pt diffusion are applied on the titanium and tantalum substrates using different laser beam polarizations. The concentration of Pt and oxygen in those substrates are measured using Energy Dispersive X-Ray Spectroscopy (EDS). The magnetic transmittance and conductivity of those substrates are measured as well. The effects of laser beam polarizations on Pt diffusion and the magnetic transmittance and conductivity of those substrates are studied. Treated Ti sheets show lower magnetic transmittance due to the increased conductivity from diffused Pt atoms. On the other hand, treated Ta sheets show higher magnetic transmittance due to reduced conductivity from oxidation. Linearly polarized light can enhance the Pt diffusion because of the excitation of local vibration mode of atoms. Laser Pt diffusion and thermo-treatment were applied on the Ta and MP35N wires. The Pt concentration in laser platinized Ta and MP35N wires was determined using EDS. The ultimate tensile strength, fatigue lives and lead tip heating in real MRI environment of those wires were measured. The lead tip hating of the platinized Ta wires is 42 % less than the as-received Ta wire. The diffused Pt increases the conductivity of Ta wires, resulting in more reflection of magnetic field. In the case of the platinized MP35N wire, the reduction in lead tip heating was only 1 °C due to low concentration of Pt. The weaker ultimate tensile strength and shorter fatigue lives of laser-treated Ta and MP35N wires may attribute to the oxidation and heating treatment.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
50
Koenen, Christian [Verfasser], Thomas F. [Akademischer Betreuer] Eibert, Thomas F. [Gutachter] Eibert i Ulrich [Gutachter] Stroth. "Steerable Millimeter-Wave Gaussian Beam Shaping Phased Array Antenna for Doppler Reflectometry of Nuclear Fusion Plasma Turbulence in ASDEX Upgrade Tokamak / Christian Koenen ; Gutachter: Thomas F. Eibert, Ulrich Stroth ; Betreuer: Thomas F. Eibert". München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1207075027/34.
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