Dissertations / Theses on the topic 'Laser beams'
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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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Ghneim, Said Nimr 1953. "Laser pulse amplification through a laser-cooled active plasma." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276868.
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Recent advances in experimental laser cooling have shown the possibility of stopping an atomic beam using the light pressure force of a counter-propagating laser wave. As an application to laser cooling, it is proposed to build a single frequency cesium laser that has a narrow linewidth. Laser cooling techniques are used to cool an atomic beam of cesium to an average velocity of 5 m/s, corresponding to a temperature of 0.2°K. Expressions of the basic forces that a laser wave exerts on atoms are derived according to a semi-classical approach. The experimental problems and methods of avoiding these problems are treated in detail. A computer Monte-Carlo simulation is used to discuss the feasibility of building the proposed laser. This simulation was done for an ensemble of 10,000 atoms of cesium, and it included the effects of the gravitational force and the related experimental variables. The possibility of building single frequency lasers that use a cooled medium of noble gases, and many other applications of laser cooling are briefly discussed at the end of this work.
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Kaluza, Malte Christoph. "Characterisation of laser-accelerated proton beams." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972318054.
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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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Singh, Abhyudai. "A mechanistic approach to tuning of MEMS resonators." Diss., Connect to online resource - MSU authorized users, 2006.
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Small, Douglas W. "Interaction of laser beams with relativistic electrons." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA337553.
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Malton, S. P. "Laser interactions with high brightness electron beams." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444964/.
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The International Linear Collider will be a high-precision machine to study the next energy frontier in particle physics. At the TeV energy scale, the ILC is expected to deliver luminosities in excess of 1034 cni" 2s_1. In order to achieve this, beam conditions must be monitored throughout the machine. Measurment of the beam emittance is essential to ensuring that the high luminosity can be provided at the interaction point. At the de sign beam sizes in the ILC beam delivery system, the Laserwire provides a non-invasive real-time method of measuring the emittance by the method of inverse Compton scattering. The prototype Laserwire at the PETRA stor age ring has produced consistent results with measured beam sizes of below 100 /nn. The Energy Recovery Linac Prototype (ERLP) is a technology testbed for the 4th Generation Light Source (4GLS). Inverse Compton scattering can be used in the ERLP as a proof of concept for a proposed 4GLS upgrade, and to produce soft X-rays for condensed matter experiments. The design constraints for the main running mode of the ERLP differ from those required for inverse Compton scattering. Suitable modifications to the optical lattice have been developed under the constraint that no new magnetic structures may be introduced, and the resulting photon distributions are described.
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McKenna, Colm Francis. "A study of laser-produced plasma beams." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492021.
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Pulsed Laser Deposition is a flexible and powerful tool for producing thin films of many materials. Optical Absorption Spectroscopy and Laser Induced Fluorescence can be used to characterise plasma plumes and jets derived from plumes to allow us to move from an empirical approach to P.ulsed Laser Deposition to a more quantitative approach. In this thesis, several aspects of such quantitative measurements are applied to titanium based plasma plumes produced using a KrF (248nm, 30ns) excimer laser system and probed using a tuneable dye laser. Using optical absorption spectroscopy we estimated the spatially resolved number density of atomic titanium in plasma plumes, produced with an average KrF laser fluence of 2.5 J/cm2 , to vary from 5 'x 1012 to 2 x 1013 cm-3 • Simultaneous laser induced fluorescence yielded an estimate of the atomic temperature of 1.7 ± 0.3 eV. The bandwidth of the pumping laser was reduced by up to 30% with an intracavity etalon in the pump laser and the LIF images produced for this and the standard case were used to calculate Ti I species temperature. The introduction of a pinhole on the main expansion axis of a plume restricts the lateral expansion and produces a 'plasma jet', generating of a more homogeneous ion source. Estimates of the temporal and spatial evolution of the relative proportion of ionic material in plasma jets were also made. A fundamental problem with the PLD process is the production of micron sized particulates during the laser ablation process. The interaction of two plasma plumes has been shown to remove particulates from the thin film. The LIF technique is used to characterise colliding plumes which are pumped by a tuneable dye laser.
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De, Kock Trevor Neil. "The development and evaluation of a Nd:YAG laser incorporating an unstable resonator." Thesis, Rhodes University, 1986. http://hdl.handle.net/10962/d1008566.
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Introduction: For approximately the last eight years the Laser Section of the National Physical Research Laboratory (NPRL) has been interested in inter alia, pulsed solid-state lasers and in particular, Nd:YAG. Investigations of various resonator types were undertaken with a view to the improvement of the laser parameters such as output energy, pulse width, beam quality and sensitivity to mirror misalignment. In 1980 a Nd: YAG laser employing a rotating prism Q-switch was constructed (Preussler (1980)). It involves rotating one of the two cavity reflectors so that they are parallel for only a brief instant in time. Typically the prism must rotate at a speed of 20 000 r.p.m. to ensure a single pulse output. Such lasers suffer from the tendency to emit multiple pulses, they are very noisy and they require frequent maintenance because of the short lifetime of the bearings. A resonator employing conventional curved mirrors and an electro-optical Q-switch was constructed in 1980 (Robertson & Preussler (1982)). In 1981 an electro-optically Q-swi tched laser making use of a crossed Porro-prism resonator was investigated due to its relative insensitivity to misalignment of the reflectors compared with the conventional mirror resonator (Nortier (1981)). Improvements in terms of output power, beam divergence and beam quality can be achieved by making use of a so-called unstable resonator. Such a laser has been investigated and is reported on in this study. Chapter 2 provides some background into laser theory and operation while chapter 3 deals with the theory of the unstable resonator. Chapter 4 provides details of the experimental equipment and techniques used in the work and chapter 5 discusses the evaluation of the project and results obtained.
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Becker, Stefan. "Dynamics and Transport of Laser-Accelerated Particle Beams." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-114449.
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Masood, Umar. "Radiotherapy Beamline Design for Laser-driven Proton Beams." Helmholtz Zentrum Dresden Rossendorf, 2018. https://tud.qucosa.de/id/qucosa%3A35640.
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Motivation: Radiotherapy is an important modality in cancer treatment commonly using photon beams from compact electron linear accelerators. However, due to the inverse depth dose profile (Bragg peak) with maximum dose deposition at the end of their path, proton beams allow a dose escalation within the target volume and reduction in surrounding normal tissue. Up to 20% of all radiotherapy patients could benefit from proton therapy (PT). Conventional accelerators are utilized to obtain proton beams with therapeutic energies of 70 – 250 MeV. These beams are then transported to the patient via magnetic transferlines and a rotatable beamline, called gantry, which are large and bulky. PT requires huge capex, limiting it to only a few big centres worldwide treating much less than 1% of radiotherapy patients. The new particle acceleration by ultra-intense laser pulses occurs on micrometer scales, potentially enabling more compact PT facilities and increasing their widespread. These laser-accelerated proton (LAP) bunches have been observed recently with energies of up to 90 MeV and scaling models predict LAP with therapeutic energies with the next generation petawatt laser systems. Challenges: Intense pulses with maximum 10 Hz repetition rate, broad energy spectrum, large divergence and short duration characterize LAP beams. In contrast, conventional accelerators generate mono-energetic, narrow, quasi-continuous beams. A new multifunctional gantry is needed for LAP beams with a capture and collimation system to control initial divergence, an energy selection system (ESS) to filter variable energy widths and a large acceptance beam shaping and scanning system. An advanced magnetic technology is also required for a compact and light gantry design. Furthermore, new dose deposition models and treatment planning systems (TPS) are needed for high quality, efficient dose delivery. Materials and Methods: In conventional dose modelling, mono-energetic beams with decreasing energies are superimposed to deliver uniform spread-out Bragg peak (SOBP). The low repetition rate of LAP pulses puts a critical constraint on treatment time and it is highly inefficient to utilize conventional dose models. It is imperative to utilize unique LAP beam properties to reduce total treatment times. A new 1D Broad Energy Assorted depth dose Deposition (BEAD) model was developed. It could deliver similar SOBP by superimposing several LAP pulses with variable broad energy widths. The BEAD model sets the primary criteria for the gantry, i.e. to filter and transport pulses with up to 20 times larger energy widths than conventional beams for efficient dose delivery. Air-core pulsed magnets can reach up to 6 times higher peak magnetic fields than conventional iron-core magnets and the pulsed nature of laser-driven sources allowed their use to reduce the size and weight of the gantry. An isocentric gantry was designed with integrated laser-target assembly, beam capture and collimation, variable ESS and large acceptance achromatic beam transport. An advanced clinical gantry was designed later with a novel active beam shaping and scanning system, called ELPIS. The filtered beam outputs via the advanced gantry simulations were implemented in an advanced 3D TPS, called LAPCERR. A LAP beam gantry and TPS were brought together for the first time, and clinical feasibility was studied for the advanced gantry via tumour conformal dose calculations on real patient data. Furthermore, for realization of pulsed gantry systems, a first pulsed beamline section consisting of prototypes of a capturing solenoid and a sector magnet was designed and tested at tandem accelerator with 10MeV pulsed proton beams. A first air-core pulsed quadrupole was also designed. Results: An advanced gantry with the new ELPIS system was designed and simulated. Simulated results show that achromatic beams with actively selectable beam sizes in the range of 1 – 20 cm diameter with selectable energy widths ranging from 19 – 3% can be delivered via the advanced gantry. ELPIS can also scan these large beams to a 20 × 10 cm2 irradiation field. This gantry is about 2.5 m in height and about 3.5 m in length, which is about 4 times smaller in volume than the conventional PT gantries. The clinical feasibility study on a head and neck tumour patient shows that these filtered beams can deliver state-of-the-art 3D intensity modulated treatment plans.
Experimental characterization of a prototype pulsed beamline section was performed successfully and the synchronization of proton pulse with peak magnetic field in the individual magnets was established. This showed the practical applicability and feasibility of pulsed beamlines. The newly designed pulsed quadrupole with three times higher field gradients than iron-core quadrupoles is already manufactured and will be tested in near future. Conclusion: The main hurdle towards laser-driven PT is a laser accelerator providing beams of therapeutic quality, i.e. energy, intensity, stability, reliability. Nevertheless, the presented advanced clinical gantry design presents a complete beam transport solution for future laser-driven sources and shows the prospect and limitations of a compact laser-driven PT facility. Further development in the LAP-CERR is needed as it has the potential to utilize advanced beam controls from the ELPIS system and optimize doses on the basis of advanced dose schemes, like partial volume irradiation, to bring treatment times further down. To realize the gantry concept, further research, development and testing in higher field and higher (up to 10 Hz) repetition rate pulsed magnets to cater therapeutic proton beams is crucial.
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Shaarawi, Mohammed Saad. "Laser chemical vapor deposition of millimeter scale three-dimensional shapes." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3023559.
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Ketprom, Urachada. "Line-of-sight propagation of optical wave through multiple-scatter channel in optical wireless communication system /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/6057.
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Arumugam, Anitha. "Development of method for measurement of passive losses in Cr²⁺:ZnSe and Cr²⁺:ZnS laser crystals using polarized laser beam." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/arumugam.pdf.
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Draper, Douglas C. "Prediction and measurement of the unwrapped phase for speckle propagating in turbulence /." Full text open access at:, 1992. http://content.ohsu.edu/u?/etd,638.
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Osterhoff, Jens. "Stable, ultra-relativistic electron beams by laser-wakefield acceleration." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-96539.
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Petkov, Theodor. "Statics and dynamics of ellipsoidal particles in laser beams." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0878/document.
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Ce travail de thèse est une contribution au projet national AMOCOPS, financé par l’ANR. Le thème central du projet est la diffusion de lumière par des particules de formes complexes et de grandes tailles (plusieurs dizaines de µm au moins), domaine où les méthodes de simulation numérique existantes trouvent leurs limites d’applicabilité. Nous abordons le problème par le biais des effets mécaniques de la lumière, autrement dit les forces et couples créés par la pression de radiation. Etant la conséquence du transfert d’impulsion entre l’onde et la matière, ces effets sont directement liés à la diffusion de lumière. La thèse comprend une partie expérimentale –majoritaire- concernant les réponses mécaniques de particules de polystyrène de forme ellipsoïdale et d’allongement variable sous illumination par un ou deux faisceaux laser. Les cas de faisceaux faiblement focalisés (lévitation optique) et d’un faisceau très fortement focalisé (pincette optique) sont examinés successivement. Nous caractérisons différents types d’équilibre statique, certains d’entre eux non décrits auparavant, obtenus dans les deux géométries. Par ailleurs nous confirmons l’existence de réponses purement dynamiques, où la particule oscille en permanence. Trois nouveaux modes sont observés, deux dans la géométrie lévitation optique et un autre sous pincette optique. Cette étude nous permet de distinguer les oscillations dites de Simpson-Hanna dans le régime linéaire de celles non linéaires mises en évidence avant nous par Mihiretie et al..Les résultats de nos expériences sont comparés à ceux obtenus par les simulations de J.C. Loudet, sur la base de la simple optique géométrique (OG) et limitées à 2 dimensions (2d). Nous montrons que ces simulations permettent de reproduire qualitativement et comprendre physiquement la plupart des comportements observés dans nos expériences. La principale limitation de ces calculs tient à ce que l’OG ignore le caractère ondulatoire de la lumière. Pour faire mieux et aller vers des simulations fiables quantitativement, il faut développer un modèle alliant optique géométrique et optique ondulatoire. C’est la fonction du modèle VCRM (Vectorial Complex Ray Model) développé récemment par K.F. Ren en 2d. Le but du projet Amocops est de mettre au point la version 3d de la méthode et de la valider sur la base d’expériences comme celles que nous avons conduites. La deuxième partie de la thèse est consacrée à la méthode VCRM. Nous en exposons les principes, et nous présentons quelques résultats des travaux en cours avec une version intermédiaire entre 2d et 3d, dite « 2d+ ». Quelques illustrations sont proposées sur des exemples impliquant des sphères et ellipsoïdes de grandes taillesThis work is a contribution to the “AMOCOPS” project, funded by Agence Nationale de la Recherche. AMOCOPS is dedicated to the development of new computation schemes to simulate the light scattering patterns of large complexly shaped particles. Particle sizes are of the order of several 10s of micrometres, which is at the limit, or beyond the capabilities of currently available computation techniques.Our work indirectly deals with light scattering through the corresponding mechanical effects of light. Light scattering is the source of momentum transfer between light and matter, and therefore of the forces and torques acting on the exposed particles. The majority of Part A of this thesis is about the mechanical responses of ellipsoidal polystyrene particles of varying aspect ratios, under illumination by one or two laser beams. We investigate the case of weakly focused beams (optical levitation), and that of a single large aperture beam (optical tweezers). Different types of static equilibria, some of which are new, are observed and characterized in both geometries. We confirm the existence of dynamic states, whereby the particle permanently oscillates within the laser beam(s). Three new oscillation modes are observed, two of them in the conditions of optical levitation, and another one in the optical tweezer geometry. The study allows us to make a distinction between noise-driven oscillations in the linear regime, of the type predicted by Simpson and Hanna, and nonlinear oscillations such as those evidenced prior to this work, by Mihiretie et al..Results from our experiments are compared to simulations by J.C. Loudet, using simple ray-optics (RO) in two dimensions (2D). We show that results from 2D-RO qualitatively match most of our observations, and allow us to physically understand the main mechanisms at work in the observed phenomena. The simulations cannot be quantitatively exact, due to the 2D limitation, and because RO essentially ignores the wave nature of light. In Part B of the manuscript, we present the principles of the Vectorial Complex Ray Model (VCRM), which was recently developed by K.F. Ren in 2d. The goal of AMOCOPS is to develop a full 3D version of VCRM, able to simulate light scattering by particles of any shape with a smooth surface. We explain the basics of the model, as well as the “2D+” version, which is an extension of the basic 2D-VCRM. A few illustrative examples of light scattering patterns computed with 2d+-VCRM for large-sizes spheres and ellipsoids are presented
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Cai, Yangjian. "Propagation of some coherent and partially coherent laser beams." Doctoral thesis, Stockholm : Electromagnetic Engineering, School of Electrical Engineering, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4034.
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Nantel, Marc. "Bunched beams from RFQ traps for laser spectroscopy studies." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59579.
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A fast-beam collinear laser spectroscopy apparatus has been designed and tested with the $ sp{23}$Na D$ sb2$ line (wavelength = 589 nm) on continuous atomic beams.A radio-frequency quadrupole ion trap and its associated electronics have been assembled and successfully operated, trapping $ sp{23}$Na$ sp{+}$ ions from an external source built for the purposes of this work. The bunched ions were extracted and detected; the effect of several injection, bunching and extraction parameters on the extracted bunches' size were studied. A simple model of the ion bunching and losses in the trap is proposed.
From the sensitivity limit of the collinear laser spectroscopy apparatus and the maximum bunched current output from the trap, the possibility of performing fast-beam collinear laser spectroscopy measurements on bunched atomic beams is examined.
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Fiorini, Francesca. "Experimental and computational dosimetry of laser-driven radiation beams." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3371/.
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Laser-driven particle acceleration is an area of increasing research interest given the recent development of short pulse high intensity lasers. A significant difficulty in this field is given by the exceptionally large instantaneous dose rates which such particle beams can produce. This represents a challenge for standard dosimetry techniques and more sophisticated procedures need to be explored. In this thesis I present novel detection and characterisation methods using a combination of GafChromic films, TLD chips, nuclear activation and Monte Carlo simulations, applicable to laser-driven beams. Part of the work is focused on the detection of laserdriven protons used to irradiate V79 cells in order to determine the feasibility of laser-driven proton therapy. A dosimetry method involving GafChromic films and numerical simulations has been appositely developed and used to obtain cell survival results, which are in agreement with those obtained by conventionally accelerated proton beams. Another part is dedicated to the detection and characterisation of laser-driven electron and X-ray beams. An innovative simulation method to obtain the temperature of the electrons accelerated by the laser, and predict the subsequently generated X-ray beam, has been developed and compared with the acquired experimental data.
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Kirby, Daniel James. "Radiation dosimetry of conventional and laser-driven particle beams." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/2816/.
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The measurement of radiation dose in radiotherapy is vital in ensuring the accuracy of treatments. As more advanced techniques using protons and ions emerge, they pose challenges to ensure the same level of accuracy of dosimetry is achieved as for conventional X-ray radiotherapy. A relatively new method of particle acceleration using ultra-high intensity lasers and thin metallic targets has sparked a large effort to investigate the possible application of this technology in radiotherapy, which in turn requires accurate methods of dosimetry to be carried out and is the main motivation for this work. Accurate dosimetry was initially performed here using an air ionisation chamber, various models of GafChromic film and a PMMA phantom in 15 and 29 MeV protons and 38 MeV \(\alpha\)-particles from the Birmingham cyclotron. In developing an accurate protocol for absorbed dose-to-water at these relatively low proton energies, new data was generated on the proton energy response of GafChromic films. This enabled accurate dosimetry of a prototype laser-particle source, and provided improvements to a method of spectroscopic measurement in the resultant mixed field of multi-energy protons, electrons and X-rays. Monte Carlo simulations using MCNPX but mainly FLUKA were performed throughout to support and verify experimental measurements.
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Jukes, Paul Richard. "Using coincident techniques to interpret the photodissociation of small cluster ions." Thesis, University of Sussex, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313971.
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DeBolt, Frederick C. "Analysis of thermal effects produced by incident laser radiation on a structure /." Online version of thesis, 1991. http://hdl.handle.net/1850/10788.
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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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Yip, Wing Lam. "Resonance-enhanced laser-induced breakdown spectroscopy : how the beam profile of the ablation laser and the interception geometry and energy of the reheating laser affect analytical performance." HKBU Institutional Repository, 2009. http://repository.hkbu.edu.hk/etd_ra/1083.
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Salehi, Dariush, and ds_salehi@yahoo com. "Sensing and control of Nd:YAG laser cladding process." Swinburne University of Technology, 2005. http://adt.lib.swin.edu.au./public/adt-VSWT20050915.142812.
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Surface engineering provides solutions to wear and corrosion degradation of engineering components. Laser cladding is a surfacing process used to produce wear and corrosion resistant surfaces by covering a particular part of the substrate with another material that has superior properties, producing a fusion bond between the two materials with minimal dilution of the clad layer by the substrate. The advantages of laser cladding compared to conventional techniques include low and controllable heat input into the workpiece, a high cooling rate, great processing flexibility, low distortion due to the low heat input to the workpiece and minimal post-treatment. The main processing parameters of laser cladding include laser power, laser spot size, processing speed, and powder feed rate. Within an optimized operational window, all these variables have some effect on the temperature of the clad interaction zone. The laser cladding technique is very complicated because it involves metallurgical and physical phenomena, such as laser beam-materials interaction, heat transfer between the clad and the substrate, and the interdiffusion of the clad and the substrate materials. Laser cladding is currently an open-loop process, relying on the skills of the operator and requiring dedication to specialty to make it successful. Unless the required expertise is provided, attempts to make the process successful will be futile. The objective in conducting the project was to investigate and develop prototype sensors to monitor and control Nd:YAG laser cladding process. Through a LabVIEW software based monitoring program, real-time process monitoring of optical emissions in the form of light and heat radiation was carried out, and correlated with the properties of the produced clad layers. During various experiments, single- and multiple-track laser cladding trials were performed. The responses of such sensors to the selected conditions were examined and an in depth analysis of detected heat and optical radiation signals was carried out. The results of these experiments showed the ability of such sensors to recognize changes in process parameters, and detected defects on layer surfaces along with the presence of oxides. A multi-function closed-loop laser power and CNC motion table feed rate control interface based on a LabVIEW platform has been designed and built, which is capable of accepting and interpreting sensors� data and adjusting accordingly the laser power and CNC motion table feed rate to produce sound clad layers. The developed dual control strategy utilized in this study forms a relatively inexpensive and less-complicated system that allows end-users to achieve lower failure rates during laser cladding (within its own limitations) and, therefore, through successful concurrent control of melt pool temperature and motion table feed rate provide better productivity and quality in the experimentally produced clad layers.
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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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Tovar, Anthony A. "Beam Modes of Lasers with Misaligned Complex Optical Elements." PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/1363.
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A recurring theme in my research is that mathematical matrix methods may be used in a wide variety of physics and engineering applications. Transfer matrix techniques are conceptually and mathematically simple, and they encourage a systems approach. Once one is familiar with one transfer matrix method, it is straightforward to learn another, even if it is from a completely different branch of science. Thus it is useful to overview these methods, and this has been done here. Of special interest are the applications of these methods to laser optics, and matrix theorems concerning multipass optical systems and periodic optical systems have been generalized here to include, for example, the effect of misalignment on the performance of an optical system. In addition, a transfer matrix technique known as generalized beam method has been derived to treat misalignment effects in complex optical systems. Previous theories used numerical or ad hoc analytical solutions to a complicated diffraction integral. The generalized beam matrix formalism was also extended to higher-order beam modes of lasers and used to study mode discrimination in lasers with misaligned complex optical elements.
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Poon, Melanie J. "In situ laser activation and renewal of solid electrodes /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487585645576915.
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Rady, Nicholas Henry Shiner David C. "Nonlinear UV laser build-up cavity an efficient design /." [Denton, Tex.] : University of North Texas, 2009. http://digital.library.unt.edu/permalink/meta-dc-9833.
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Du, Preez Neil Carl. "Flattened Gaussian beam for laser paint removal." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/6905.
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Thesis (MSc)--Stellenbosch University, 2011.ENGLISH ABSTRACT: Lasers are commonly used in the industry for various applications such as laser cutting, laser drilling, lithography, medical applications, surface cleaning and a myriad of other applications. In any application of a laser the beam properties are significant. In the paint removal application discussed in this thesis, the beam properties of the laser beam can have a large impact on the efficiency of the paint removal process. The pulse energy or the average output power of the laser is normally an important parameter in laser materials processing applications. The spatial profile or intensity distribution of the beam also has an influence on the process. The propagation of the laser beam from the laser to the working point is also significant in applying the laser beam to the material. In the ideal scenario one would like to control all the parameters of the laser in terms of the output, in energy or output power, the propagation of the laser beam and the intensity distribution of the beam. The process of laser-based paint removal is no different to this. In this process a TEA CO2 laser is used for the ablation of paint from a substrate. In this application high pulse energy is required from the laser together with good beam propagation properties for delivery of the beam over a long distance. For this application the multimode beam of the TEA CO2 laser can be applied for the paint removal. The multimode beam has sufficiently high pulse energy for the paint removal process, but is not suitable for propagating over long distances through a beam path with a finite aperture. Furthermore the multimode beam does not have a uniform energy intensity distribution. It would therefore be ideal if the TEA CO2 laser could be designed with a custom beam that has a uniform intensity distribution, high pulse energy and good beam propagation. These requirements lead to the study of flattened irradiance profile laser beams. In this thesis flattened irradiance profile beams in the form of Flattened Gaussian beams are investigated. The theory of the Flattened Gaussian profile as well as the propagation of the beam is investigated. Furthermore the generation of such a beam internally to the laser resonator is studied. In succession to this a custom laser resonator was designed and implemented on the TEA CO2 laser. The resulting Flattened Gaussian Beam was characterised and applied to the application of laser paint removal. It was finally shown that the Flattened Gaussian Beam could be successfully generated and applied with equal success in the application of laser paint removal.
AFRIKAANSE OPSOMMING: Lasers word algemeen in die industrie gebruik vir toepassings soos laser snywerk, laser boorwerk, litografie, mediese toepassings, oppervlakreiniging en verskeie ander. In enige toepassing van 'n laser is die eienskappe van die laserbundel van groot belang vir die proses. In die verf verwydering toepassing wat bespreek word in hierdie tesis het die bundel eienskappe 'n groot invloed op die effektiwiteit van die verf stropings proses. Die pulsenergie of uitset drywing van die laser is gewoonlik 'n belangrike parameter in 'n materiaalverwerkings toepassing. Die ruimtelike profiel of energie intensiteitprofiel van die bundel het ook 'n invloed op die proses. Die voortplanting van die bundel vanaf die laser na die werkspunt het ook 'n beduidende invloed op die toepassing van die laserbundel op die materiaal. In die ideale geval sal mens graag al die parameters van die laserbundel soos pulsenergie of drywing, die bundel voortplanting en energie intensiteitprofiel wil beheer. Die toepassing van die laser vir verfverwydering vereis ook die beheer van hierdie unieke parameters wat reeds genoem is. In hierdie proses is 'n TEA CO2 laser gebruik vir die verwydering van verf van 'n substraat. Die toepassing vereis hoë pulsenergie saam met goeie bundel voortplantingseienskappe vir lewering van die bundel oor lang afstande. Die multimode bundel van die laser kan gebruik word vir hierdie toepassing. Die multimode bundel bevat genoegsame energie vir die verfstropings proses maar is nie geskik vir voortplanting oor lang afstande deur 'n bundelpad wat 'n beperking op die bundel grootte het nie. Verder het die multimode bundel ook nie 'n uniforme energie intensiteitprofiel nie. Dit sou ideal wees as die TEA CO2 laser toegerus kon word met 'n toepassingsgerigte bundel wat hoë puls energie, goeie bundel voortplanting en 'n uniforme intensiteitprofiel het. Hierdie vereiste het gelei tot die studie van laserbundels met 'n uniforme plat energie intensiteitprofiel. In hierdie tesis word plat intensiteit bundels in die vorm van plat Gaussiese bundels ondersoek. Die teorie van plat Gaussiese bundels sowel as die voortplanting van hierdie bundels word hier ondersoek. Verder word die opwekking van hierdie bundels intern tot die laserresonator ook ondersoek. Na die ondersoek is daar oorgegaan in die ontwerp en implementering van 'n doelgemaakte resonator op 'n TEA CO2 laser. Die resonator het 'n plat Gaussiese bundel as uitset gelewer. Die bundel was gevolglik gekarakteriseer en aangewend in 'n verfstropings toepassing. Ten einde is daar getoon dat 'n plat Gaussiese bundel suksesvol opgewek en toegepas kon word.
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Stoer, Marcell. "Molecular beam laser Stark spectroscopy of highly vibrationally excited molecules." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ34285.pdf.
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Tresca, Olivier. "Optimisation and control of high intensity laser accelerated ion beams." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=16842.
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The interaction of a laser pulse of relativistic intensity (≥1×1018 Wcm−2) with a solid target results in the creation of a quasi-electrostatic field at the rear surface of the target. This field is strong enough (TVm−1) to ionise and accelerate ions from the target surface via the Target Normal Sheath Acceleration (TNSA) mechanism. The resulting beam has many desirable properties for a large range of potential applications. The work presented in this thesis aims at optimising and controlling the ion beam properties. Firstly, an investigation of laser driven ion acceleration using ultrahigh contrast (1010), ultrashort (50 fs) laser pulses focused to intensities up to 1021 Wcm−2 on thin foil targets is presented. It is found that irradiation at normal (0◦) incidence produces higher energy ions than oblique incidence (35◦), contrasting sharply with previous work at lower intensities. These findings are confirmed by 1D boosted PIC simulations and can be explained by the acceleration of fast electrons being dominated by a new absorption process. The effects of target composition and thickness on the acceleration of carbon ions are also discussed and compared to calculations using analytical models of ion acceleration. Next, an investigation of the transverse refluxing of fast electrons in targets of limited lateral size is reported. The targets were irradiated by high intensity (∼1×1019 Wcm−2), picosecond laser pulses. The maximum energy of the resulting TNSA proton beams is found to increase with decreasing target surface area. This is explained by the presence of a laterally spreading electron population that reflects off the target edges and enhances the TNSA accelerating field. In addition it is demonstrated that this laterally refluxing electron population can be used to control the spatial intensity distribution of the TNSA proton beam, by changing the geometry of the target. This technique offers encouraging prospects for many applications of laser accelerated ions. Finally, a characterisation study of debris emission generated by the interaction of high power laser pulses with solid targets is presented. Targets of thickness ranging from 1 mm to 5 nm were irradiated by high intensity (∼1×1020 Wcm−2), picosecond laser pulses. The resulting debris emission is found to be directed along the target normal axis at both the rear and front of the target. The front emission profile is found to be similar to a plasma expansion profile. Hollow debris depositions of radius increasing with target thickness are measured from the target rear surface. This emission profile is explained by the propagation and breakout of a laser driven shock at the rear of the target.
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Pedregosa, Gutierrez J. "Intense femtosecond laser interactions with ions in beams and traps." Thesis, Queen's University Belfast, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432513.
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Byrne, Nicole (Nicole Malenie). "Phase stabilization of laser beams in a cold atom accelerometer." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/96460.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 95-97).
A cold atom accelerometer measures the displacement of a proof mass of laser cooled atoms with respect to an instrument reference frame. The cold atom interferometer's reference frame is defined by a pair of specially prepared, counter-propagating laser beams, that measure inertially induced atom displacements with nm scale resolution. This corresponds to acceleration sensitivities comparable to state of the art electro-mechanical accelerometers. In dynamic environments, sensitivity is limited by the stability of the relative laser phase of the two interrogation laser beams, which is adversely affected by vibrations and temperature fluctuations of the interrogation beam optics. Without an independent measurement, the cold atom interferometer cannot distinguish platform acceleration from laser phase fluctuations, which thus are a potentially serious source of error. In this thesis, a Michelson optical interferometer and an optical feedback loop were used to stabilize the relative phase of the interrogation laser beams in a cold atom accelerometer. A digital controller stabilized the relative phase via an electro-optic phase modulator. This control loop's bandwidth encompasses 98.8% of the noise power as determined from the power spectral density of the open loop 795nm Michelson signal. Increasing the controller bandwidth would gain the system marginal improvement in noise reduction. At an atom interferometer dwell time of 1 msec, active laser phase stabilization improved the atom interferometer sensitivity; at an atom interferometer dwell time of 8msec, an improvement was no longer evident. Improvements to the laser phase stabilization system are proposed to increase atom interferometer stability at longer dwell times.
by Nicole Byrne.
S.M.
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Rehfeld, Niklas Sebastian. "The theory of the manipulation of molecules with laser beams." [S.l. : s.n.], 2002. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10162238.
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Caron, Christian Frédéric Roger Caron. "Harmonic generation in gases using Bessel-Gauss beams." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4668/.
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The generation and propagation of harmonics in an atomic gas are described for the case of an incident Bessel-Gauss beam. Theoretical expressions are derived for the far-field amplitude of the harmonic field by solving the propagation equation using an elaborate integral formalism. We establish simple rules which determine the optimum Bessel-Gauss beam with respect to phase-matching as a function of the medium properties, such as the dispersion and the gas density. Target depletion due to photoionization and refractive index variations originating from both free electrons and dressed linear atomic susceptibilities are taken into account. The intensity-dependent complex atomic dipole moment is calculated using nonpertur- bative methods. Numerical propagation calculations for hydrogen, xenon and argon are presented. For hydrogen we consider the third harmonic of a 355-nm, 15-ps pump beam up to 3 X 10(^13) W/cm(^2) intensity, similarly for xenon, but at lower intensities. For argon we consider the 17th and 19th harmonic of a 810-nm, 30-fs pump beam around 10(^14) W/cm(^2) intensity. We compare conversion efficiencies and both spatial and temporal far-field profiles for an optimized Bessel-Gauss beam with respect to a Gaussian beam of same power and/or peak focal intensity. For the case of hydrogen, we investigate the effect of an ac-Stark-shift induced atomic resonance. We find all results in good agreement with our theoretical predictions. We conclude from our studies that Bessel-Gauss beams can perform better in terms of conversion efficiency than a comparable Gaussian beam. We find this to originate essentially from the more flexible phase-matching conditions for Bessel-Gauss beams. Bessel-Gauss beams also allow for spatial separation of the harmonic and the incident field in the far-field region, owing to the conical shape of their spatial far-field profile. Both features make Bessel-Gauss beams an attractive alternative to Gaussian beams in a limited but substantial number of experimental conditions.
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Cheshkov, Sergey Valeriev. "Noise effects, emittance control, and luminosity issues in laser wakefield accelerators /." Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008301.
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Ng, Jack Tsz Fai. "Light-induced forces on small particles /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202005%20NG.
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Alameer, Maryam. "Polarization Dependent Ablation of Diamond with Gaussian and Orbital Angular Momentum Laser Beams." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39850.
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The vectorial nature (polarization) of light plays a significant role in light-matter interaction
that leads to a variety of optical devices. The polarization property of light
has been exploited in imaging, metrology, data storage, optical communication and
also extended to biological studies. Most of the past studies fully explored and dealt
with the conventional polarization state of light that has spatially symmetric electrical
field geometry such as linear and circular polarization. Recently, researchers
have been attracted to light whose electric field vector varies in space, the so-called
optical vector vortex beam (VVB). Such light is expected to further enhance and
improve the efficiency of optical systems. For instance, a radially polarized light
under focusing condition is capable of a tighter focus more than the general optical
beams with a uniform polarization structure, which improves the resolution of the
imaging system [1].
Interaction of ultrafast laser pulses with matter leads to numerous applications
in material processing and biology for imaging and generation of microfluidic systems.
A femtosecond pulse, with very high intensities of (10^{12} - 10^{13} W/cm^2), has
the potential to trigger a phenomenon of optical breakdown at the surface and therefore
induce permanent material modification. With such high intensities and taking
into account the fact that most materials possess large bandgap, the interaction is
completely nonlinear in nature, and the target material can be modified locally upon the surface and even further in bulk. The phenomenon of optical breakdown can be
further investigated by studying the nonlinear absorption. Properties like very short
pulse duration and the high irradiance of ultrashort laser pulse lead to more precise
results during the laser ablation process over the long pulsed laser. The duration of
femtosecond laser pulse provides a high resolution for material processing because
of the significant low heat-affected zone (HAZ) beyond the desired interaction spot
generated upon irradiating the material. Under certain condition, the interaction
of intense ultrashort light pulses with the material gives rise to the generation of
periodic surface structures with a sub-micron periodicity, i.e., much smaller than the
laser wavelength. The self-oriented periodic surface structures generated by irradiating
the material with multiple femtosecond laser pulses results in improving the
functionality of the material's surface such as controlling wettability, improving thin
film adhesion, and minimizing friction losses in automobile engines, consequently,
influences positively on many implementations.
In this work, we introduced a new method to study complex polarization states
of light by imprinting them on a solid surface in the form of periodic nano-structures.
Micro/Nanostructuring of diamond by ultrafast pulses is of extreme importance because
of its potential applications in photonics and other related fields.
We investigated periodic surface structures usually known as laser-induced periodic surface
structures (LIPSS) formed by Gaussian beam as well as with structured light carrying
orbital angular momentum (OAM), generated by a birefringent optical device
called a q-plate (QP). We generated conventional nano-structures on diamond
surface using linearly and circularly polarized Gaussian lights at different number
of pulses and variable pulse energies. In addition, imprinting the complex polarization state of different orders of optical vector vortex beams on a solid surface was fulfilled in the form of periodic structures oriented parallel to the local electric field of optical light. We also produced a variety of unconventional surface structures by superimposing a Gaussian beam with a vector vortex beam or by superposition of different order vector vortex beams.
This thesis is divided into five chapters, giving a brief description about laser-matter
interaction, underlying the unique characterization of femtosecond laser over
the longer pulse laser and mechanisms of material ablation under the irradiation of
fs laser pulse. This chapter also presents some earlier studies reported in formation
of (LIPSS) fabricated on diamond with Gaussian. The second chapter explains the
properties of twisted light possessing orbital angular momentum in its wavefront, a
few techniques used for OAM generation including a full explanation of the q-plate
from the fabrication to the function of the q-plate, and the tool utilized to represent
the polarization state of light (SoP), a Poincar'e sphere. Finally, the experimental details and results are discussed in the third and fourth chapters, respectively,
following with a conclusion chapter that briefly summarizes the thesis and some
potential application of our findings.
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Osman, Frederick, of Western Sydney Macarthur University, and Faculty of Business and Technology. "Nonlinear paraxial equation at laser plasma interaction." THESIS_FBT_XXX_Osman_F.xml, 1998. http://handle.uws.edu.au:8081/1959.7/280.
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This thesis presents an investigation into the behaviour of a laser beam of finite diameter in a plasma with respect to forces and optical properties, which lead to self-focusing of the beam. The transient setting of ponderomotive nonlinearity in a collisionless plasma has been studied, and consequently the self- focusing of the pulse, and the focusing of the plasma wave occurs. The description of a self-focusing mechanism of laser radiation in the plasma due to nonlinear forces acting on the plasma in the lateral direction, relative to the laser has been investigated in the non-relativistic regime. The behaviour of the laser beams in plasma, which is the domain of self-focusing at high or moderate intensity, is dominated by the nonlinear force. The investigation of self-focusing processes of laser beams in plasma result from the relativistic mass and energy dependency of the refractive index at high laser intensities. Here the relativistic effects are considered to evaluate the relativistic self-focusing lenghts for the neodymium glass radiation, at different plasma densities of various laser intensities. A sequence of code in C++ has been developed to explore in depth self-focusing over a wide range of parameters. The nonlinear plasma dielectric function to relativistic electron motion will be derived in the latter part of this thesis. From that, one can obtain the nonlinear refractive index of the plasma and estimate the importance of relativistic self-focusing as compared to ponderomotive non-relativistic self-focusing, at very high laser intensities. When the laser intensity is very high, pondermotive self-focusing will be dominant. But at some point, when the oscillating velocity of the plasma electron becomes very large, relativistic effects will also play a role in self-focusing. A numerical and theoretical study of the generation and propagation of oscillation in the semiclassical limit of the nonlinear paraxial equation is presented in this thesis. In a general setting of both dimension and nonlinearity, the essential differences between the 'defocusing' and 'focusing' cases hence is identified. Presented in this thesis are the nonlinearity and dispersion effects involved in the propagation of solitions which can be understood by using a numerical routines were implemented through the use of the mathematica program, and results give a very clear idea of this interesting phenomenaDoctor of Philosophy (PhD)
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Chalus, Olivier Jean. "Study of nonlinear effects of intense UV beams in the atmosphere." Université Louis Pasteur (Strasbourg) (1971-2008), 2007. https://publication-theses.unistra.fr/public/theses_doctorat/2007/CHALUS_Olivier_Jean_2007.pdf.
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Les faisceaux lasers de hautes puissances déclenchent durant leur propagation la formation d’effets nonlinéaires. Si l’intensité est suffisamment élevée l’accumulation de ces effets peut provoquer un mode de propagation s’approchant des caractéristiques des guides d’ondes. Ce phénomène est appelé filamentation. Il est amplement complexe et extensivement étudié pour les faisceaux IR mais injustement ignoré pour l’UV. Dans cette thèse, l’étude du cas UV est traitée. Une double étude théorique pour caractériser le profil du faisceau et sa propagation est développée. Ensuite l’étude expérimentale est réalisée en commencant par la construction du laser permettant une telle étude, puis les résultats expérimentaux de la filamentation UV. Les résultats théoriques et l’observation expérimentales mènent tous deux à l’observation de la propagation d’un faisceau UV de environ 600microns pour une durée d’impulsion de 200ps et une énergie de l’ordre de 200mJHigh power laser beams involve, during their propagation, the formation of nonlinear effects. If the intensity is high enough the accumulation of those effects can induce a mode of propagation close to the characteristics of waveguides. This phenomenon is called filamentation. It is complex and extensively studied for IR beams but unfairly ignored for the UV. In this dissertation, the case of the UV is studied. A double theoretical study is conducted for the shape of the beam profile and for the propagation. Then an experimental study is conducted, starting from the construction of the laser allowing such study to the experimental results of UV filamentation. The theoretical and experimental results lead both to the observation of the propagation of UV beams of about 600microns for pulse duration of 200ps and energy on the order of 200mJ
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Bussmann, Michael. "Laser-Cooled Ion Beams and Strongly Coupled Plasmas for Precision Experiments." Diss., lmu, 2008. http://nbn-resolving.de/urn:nbn:de:bvb:19-97290.
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Yalukova, Olga. "Interaction mechanisms of pulsed laser beams at different wavelengths with matter." Licentiate thesis, Luleå, 2004. http://epubl.luth.se/1402-1757/2004/029.
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Sutton, George M., and Oscar Biblarz. "Investigations of self-pumped phase conjugate laser beams and coherence length." Thesis, Monterey, California. Naval Postgraduate School, 1993. http://hdl.handle.net/10945/24187.
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Hickman, Christopher Guy. "Laser spectroscopic studies in molecular beams, clusters and at liquid interfaces." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239652.
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Brenner, Ceri M. "Laser-driven proton beams : mechanisms for spectral control and efficiency enhancement." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18234.
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This thesis reports on investigations of proton acceleration driven by the interaction of short, intense laser pulses with thin, solid targets. Laser-driven plasma interactions are used to establish accelerating quasi-electrostatic field gradients, on the rear surface of the target, that are orders of magnitude higher than the current limit of conventional, radio-frequency-based accelerator technology. The resulting high energy (multi-MeV) proton beams are highly laminar, have ultra-low emittance, and the inherently broad energy spectrum is particularly effective for use in proton imaging, heating and transmutation applications. This thesis reports on a series of investigations carried out to explore routes towards control of the spectral properties of laser-driven proton sources and optimisation of laser-to-proton energy conversion efficiency. The dependence of laser accelerated proton beam properties on laser energy and focal spot size in the interaction of an intense laser pulse with an ultra-thin foil is explored at laser intensities of 1016-1018 W/cm2. The results indicate that whilst the maximum proton energy is dependent on both these laser pulse parameters, the total number of protons accelerated is primarily related to the laser pulse energy. A modification to current analytical models of the proton acceleration, to take account of lateral transport of electrons on the target rear surface, is suggested to account for the experimental findings. The thesis also reports on an investigation of optical control of laser-driven proton acceleration, in which two relativistically intense laser pulses, narrowly separated in time, are used. This novel approach is shown to deliver a significant enhancement in the coupling of laser energy to medium energy (5-30 MeV) protons, compared to single pulse irradiation. The 'double-pulse' mechanism of proton acceleration is investigated in combination with thin targets, for which refluxing of hot electrons between the target surfaces can lead to optimal conditions for coupling laser drive energy into the proton beam. A high laser-to-proton conversion efficiency is measured when the delay between the pulses is optimised at 1 ps. The subsequent effect of double-pulse drive on the angular distribution of the proton beam is also explored for thick targets.
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Murphy, Christopher Dominic. "Diagnosis of high energy electron beams produced by laser wakefield accelerators." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485694.
Full textAbstract:
This thesis discusses the production and diagnosis of electron bunches from laser produced wakefields. For the right laser and plasma parameters, monoenergetic features were observed in the electron spectrum. These mononenergetic beams are found to be sensitive to plasma density and laser parameters. In particular, the beams were found to show shot-to-shot variations in energy and pointing. Simulations were performed to study the mechanism of electron injection and acceleration. Further results demonstrate how the intermittancy of the electron beam may at times be an artifact caused by pointing instabilities. This thesis also discusses the first reported experimental observation of photon acceleration from a laser-produced wakefield. The spectrum of the transmitted light from a wakefield accelerator was measured. A large density dependent blue-shifted portion of the light was observed which cannot be explained by flash ionisation. A photon kinetic model of the experiment demonstrates that this blue-shifting occurs at the back of the pulse. Here, the moving density gradient of the wake provides a time varying refractive index suitable for photon acceleration. Thus comparison between theory and experiment allows one to optically characterise the wakefield accelerating structure. Finally the thesis presents experimental measurements of the electron bunch duration. A chirped probe pulse is passed through a birefringent (ZnTe) crystal close to the wakefield generated electron bunch. Frequency components of the probe pulse that coincide temporally with the Coulomb field of the electrons at the location of the crystal experience a rotation of polarization due to the induced Kerr effect. Measuring the spectrum of the rotated component, allows calculation of the electron bunch duration. Limitations to the technique are discussed and the methods used to overcome limitations are described. The results presented in this thesis constitute the highest resolution measurement of single laser produced electron bunches thus far.
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Mayo, M. E. "Interaction of laser radiation with urinary calculi." Thesis, Department of Applied Science, Security and Resillience, 2009. http://hdl.handle.net/1826/4013.
Full textAbstract:
Urolithias, calculus formation in the urinary system, affects 5 – 10% of the population
and is a painful and recurrent medical condition. A common approach in the treatment
of calculi is the use of laser radiation, a procedure known as laser lithotripsy, however,
the technique has not yet been fully optimised. This research examines the experimental
parameters relevant to the interactions of the variable microsecond pulsed holmium
laser (λ = 2.12 μm, τp = 120 – 800 μs, I ~ 3 MW cm-2) and the Q-switched neodymium
laser (λ = 1064 nm, τp = 6 ns, I ~ 90 GW cm-2) with calculi.
The laser-calculus interaction was investigated from two perspectives: actions that lead
to calculus fragmentation through the formation of shockwave and plasma, and the
prospect of material analysis of calculi by laser induced breakdown spectroscopy
(LIBS) to reveal elemental composition. This work is expected to contribute to
improved scientific understanding and development of laser lithotripsy.
The results support the general model of thermal and plasma processes leading to
vaporization and pressure pulses. Nd:YAG laser interaction processes were found to be
plasma-mediated and shockwave pressure (~ 12 MPa) dependent on plasma and
strongly influenced by metal ions. Ho:YAG laser-induced shockwaves (~ 50 MPa) were
found to be due to direct vaporisation of water and dependent on laser pulse duration.
The characteristics of the pressure pulse waveforms were found to be different, and the
efficiency and repeatability of shockwave and the nature of the dependencies for the
lasers suggest different bubble dynamics.
For the Nd:YAG laser, LIBS has been demonstrated as a potential tool for in situ
analysis of calculus composition and has been used for the identification of major and
trace quantities of calcium, magnesium, sodium, potassium, strontium, chromium, iron,
copper, lead and other elements.
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Knetsch, Alexander [Verfasser], and Bernhard [Akademischer Betreuer] Hidding. "Acceleration of laser-injected electron beams inan electron-beam driven plasma wakefieldaccelerator / Alexander Knetsch ; Betreuer: Bernhard Hidding." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/115388433X/34.
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