Dissertations / Theses on the topic 'Laser processing'
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O'Neill, William. "Mixed wavelength laser processing." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46479.
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Patz, Timothy Matthew. "Laser Processing of Biological Materials." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7451.
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I have explored the use of the matrix assisted pulsed laser evaporation (MAPLE) and MAPLE direct write (MDW) to create thin films of biological materials. MAPLE is a novel physical vapor deposition technique used to deposit thin films of organic materials. The MAPLE process involves the laser desorption of a frozen dilute solution (1-5%) containing the material to be deposited. A focused laser pulse (~200 mJ/cm2) impacts the frozen target, which causes the solvent to preferentially absorb the laser energy and evaporate. The collective action of the evaporated solvent desorbs the polymeric solute material towards the receiving substrate placed parallel and opposite to the target. The bioresorbable polymer PDLLA and the anti-inflammatory pharmaceutical dexamethasone were processed using MAPLE, and characterized using Fourier transform infrared spectroscopy, atomic force microscopy and x-ray photoelectron spectroscopy. MDW is a CAD/CAM controlled direct writing process. The material to be transferred is immersed in a laser-absorbing matrix or solution and coated onto a target or support positioned microns to millimeters away from a receiving substrate. Using a UV microscope objective, a focused laser pulse is directed at the backside of the ribbon, so that the laser energy first interacts with the matrix at the ribbon/matrix interface. This energy is used to gently desorb the depositing material and matrix onto the receiving substrate. I have deposited neuroblasts within a three-dimensional extracellular matrix. These two laser processing techniques have enormous potential for functional medical device and tissue engineering applications.
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Beck, Rainer Johannes. "Adaptive optics for laser processing." Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2462.
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The overall aim of the work presented in this thesis is to develop an adaptive optics (AO) technique for application to laser-based manufacturing processes. The Gaussian beam shape typically coming from a laser is not always ideal for laser machining. Wavefront modulators, such as deformable mirrors (DM) and liquid crystal spatial light modulators (SLM), enable the generation of a variety of beam shapes and furthermore offer the ability to alter the beam shape during the actual process. The benefits of modifying the Gaussian beam shape by means of a deformable mirror towards a square flat top profile for nanosecond laser marking and towards a ring shape intensity distribution for millisecond laser drilling are presented. Limitations of the beam shaping capabilities of DM are discussed. The application of a spatial light modulator to nanosecond laser micromachining is demonstrated for the first time. Heat sinking is introduced to increase the power handling capabilities. Controllable complex beam shapes can be generated with sufficient intensity for direct laser marking. Conventional SLM devices suffer from flickering and hence a process synchronisation is introduced to compensate for its impact on the laser machining result. For alternative SLM devices this novel technique can be beneficial when fast changes of the beam shape during the laser machining are required. The dynamic nature of SLMs is utilised to improve the marking quality by reducing the inherent speckle distribution of the generated beam shape. In addition, adaptive feedback on the intensity distribution can further improve the quality of the laser machining. In general, beam shaping by means of AO devices enables an increased flexibility and an improved process control, and thus has a significant potential to be used in laser materials processing.
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Lutey, Adrian Hugh Alexander <1986>. "High-Speed Laser Processing of Thin Single and Multi-Layer Films." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5741/1/Lutey_Adrian_tesi.pdf.
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Theoretical models are developed for the continuous-wave and pulsed laser incision and cut of thin single and multi-layer films. A one-dimensional steady-state model establishes the theoretical foundations of the problem by combining a power-balance integral with heat flow in the direction of laser motion. In this approach, classical modelling methods for laser processing are extended by introducing multi-layer optical absorption and thermal properties. The calculation domain is consequently divided in correspondence with the progressive removal of individual layers. A second, time-domain numerical model for the short-pulse laser ablation of metals accounts for changes in optical and thermal properties during a single laser pulse. With sufficient fluence, the target surface is heated towards its critical temperature and homogeneous boiling or "phase explosion" takes place. Improvements are seen over previous works with the more accurate calculation of optical absorption and shielding of the incident beam by the ablation products. A third, general time-domain numerical laser processing model combines ablation depth and energy absorption data from the short-pulse model with two-dimensional heat flow in an arbitrary multi-layer structure. Layer removal is the result of both progressive short-pulse ablation and classical vaporisation due to long-term heating of the sample. At low velocity, pulsed laser exposure of multi-layer films comprising aluminium-plastic and aluminium-paper are found to be characterised by short-pulse ablation of the metallic layer and vaporisation or degradation of the others due to thermal conduction from the former. At high velocity, all layers of the two films are ultimately removed by vaporisation or degradation as the average beam power is increased to achieve a complete cut. The transition velocity between the two characteristic removal types is shown to be a function of the pulse repetition rate. An experimental investigation validates the simulation results and provides new laser processing data for some typical packaging materials.
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Lutey, Adrian Hugh Alexander <1986>. "High-Speed Laser Processing of Thin Single and Multi-Layer Films." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5741/.
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Theoretical models are developed for the continuous-wave and pulsed laser incision and cut of thin single and multi-layer films. A one-dimensional steady-state model establishes the theoretical foundations of the problem by combining a power-balance integral with heat flow in the direction of laser motion. In this approach, classical modelling methods for laser processing are extended by introducing multi-layer optical absorption and thermal properties. The calculation domain is consequently divided in correspondence with the progressive removal of individual layers. A second, time-domain numerical model for the short-pulse laser ablation of metals accounts for changes in optical and thermal properties during a single laser pulse. With sufficient fluence, the target surface is heated towards its critical temperature and homogeneous boiling or "phase explosion" takes place. Improvements are seen over previous works with the more accurate calculation of optical absorption and shielding of the incident beam by the ablation products. A third, general time-domain numerical laser processing model combines ablation depth and energy absorption data from the short-pulse model with two-dimensional heat flow in an arbitrary multi-layer structure. Layer removal is the result of both progressive short-pulse ablation and classical vaporisation due to long-term heating of the sample. At low velocity, pulsed laser exposure of multi-layer films comprising aluminium-plastic and aluminium-paper are found to be characterised by short-pulse ablation of the metallic layer and vaporisation or degradation of the others due to thermal conduction from the former. At high velocity, all layers of the two films are ultimately removed by vaporisation or degradation as the average beam power is increased to achieve a complete cut. The transition velocity between the two characteristic removal types is shown to be a function of the pulse repetition rate. An experimental investigation validates the simulation results and provides new laser processing data for some typical packaging materials.
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Gulia, Kiran. "Pulsed laser processing of dielectric materials." Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/2035.
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The thesis investigates the wavelength dependent laser ablp..~ion in dielectric materials used for the fabrication ofhigh density Printed Circuit Boards (PCBs) in the electronics industry. Here the market for consumer and industrial products of ever-rising complexity has led to a demand for increased miniaturisation and low costs of multilevel printed circuit boards (PCBs) interconnected by microvias, which electrically connect the various circuit layers. Laser machining offers a potential solution to this need. The main objective of the research is to investigate the wavelength-dependence of the laser machining/drilling efficiency of two important sets of PCB materials, categorised as Organics and Ceramics using a carbon dioxide laser which can be tuned across its emission spectrum in the 9flm - 11 flm spectral region.. The organics include commercially available electronic materials with trade names such as Kapton, ArIon, FR4 and RCC and the ceramics materials studied are alumina and low temperature cofired ceramic (LTCC). The aim is to determine the optimum laser wavelength for maximum processing efficiency Le. to find the wavelength where the laser parameters are best matched to the optical, thermal and mechanical properties of each of the materials. A CO2 laser machining system was constructed which incorporated a novel laser source developed in the research programmes. The laser source was a MOPA system with a line-tuneable cw oscillator and a five pass power planar waveguide rf discharge-excited power operating in the so-called enhanced power regime to produce maximum peak power. An Acousto-optic modulator between the master oscillator and the amplifier allowed convenient control of pulse amplitude and duration. The system enabled the wavelength dependent studies on the wavelength and pulse energy dependence of the laser ablation properties (e.g. ablation threshold fluence and ablation rates) - to derive the so-called 'ablation spectrum' of the selected materials A comparison is made of the wavelength dependence of ablation with the room temperature absorption spectrum measured for each material using ellipsometry. It was observed that the 'ablation spectrum' information does not always appear to match the simple expectations derived from the room temperature 'absorption spectrum' of the material. This disparity in results is likely due to the change of absorption properties of • material because of rise in temperature, chemical decomposition or melting of material during ablation. However, the room temperature absorption spectrum (while not adequate alone), did provide a useful guide to the selection of a sub-set of the 40+ lines that would otherwise have to be studied. The results may be of direct application in the electronics industry to increase the efficiency oflaser machining.
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Holmberg, Patrik. "Laser processing of Silica based glass." Doctoral thesis, KTH, Laserfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173929.
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The main topic of this thesis work is photosensitivity and photo-structuring of optical fibers and bulk glass. Although research in the field of photosensitivity in glass and optical fibers has been ongoing for more than three decades, the underlying mechanisms are still not well understood. The objective was to gain a better understanding of the photo-response by studying photosensitivity from a thermodynamic perspective, as opposed to established research focusing on point defects and structural changes, and strain and stress in optical fibers. Optical fibers was mainly used for experimental studies for two reasons; first, photosensitivity in fibers is more pronounced and more elusive compared to its bulk counterpart, and secondly, fibers provide a simplified structure to study as they experimentally can be seen as one-dimensional.Initially, ablation experiments on bulk glass were performed using picosecond infrared pulses. With a design cross section of 40x40 μm, straight channels were fabricated on the top (facing incident light) and bottom side of the sample and the resulting geometries were analyzed. The results show a higher sensitivity to experimental parameters for bottom side ablation which was ascribed to material incubation effects. Moreover, on the top side, the resulting geometry has a V-shape, independent of experimental parameters, related to the numerical aperture of the focusing lens, which was ascribed to shadowing effects.After this work, the focus shifted towards optical fibers, UV-induced fiber Bragg gratings (FBGs) and thermal processing with conventional oven and with a CO2 laser as a source of radiant heat.First, a system for CO2 laser heating of optical fibers was constructed. For measuring the temperature of the processed fibers, a special type of FBG with high temperature stability, referred to as "Chemical Composition Grating" (CCG) was used. A thorough characterization and temperature calibration was performed and the results show the temperature dynamics with a temporal resolution of less than one millisecond. The temperature profile of the fiber and the laser beam intensity profile could be measured with a spatial resolution limited by the grating length and diameter of the fiber. Temperatures as high as ~ 1750 °C could be measured with corresponding heating and cooling rates of 10.500 K/s and 6.500 K/s.Subsequently, a thorough investigation of annealing and thermal regeneration of FBGs in standard telecommunication fibers was performed. The results show that thermal grating regeneration involves several mechanisms. For strong regeneration, an optimum annealing temperature near 900 C was found. Two different activation energies could be extracted from an Arrhenius of index modulation and Braggv iwavelength, having a crossing point also around 900 °C, indication a balance of two opposing mechanisms.Finally, the thermal dynamics and spectral evolution during formation of long period fiber gratings (LPGs) were investigated. The gratings were fabricated using the CO2 laser system by periodically grooving the fibers by thermal ablation. Transmission losses were reduced by carefully selecting the proper processing conditions. These parameters were identified by mapping groove depth and transmission loss to laser intensity and exposure time.Huvudtemana i denna avhandling är fotokänslighet och fotostrukturering av optiska fibrer och bulk glas. Trots att forskning inom fotokänslighet i glas och optiska fibrer har pågått under mer än tre decennier är de bakomliggande mekanismerna ännu inte klarlagda. Syftet var att få en bättre förståelse för fotoresponsen genom att studera fotokäsligheten ur ett termodynamiskt perspektiv, i motsats till etablerad forskning med fokus på punktdefekter och strukturförändringar, samt mekaniska spännings effekter i optiska fibrer. Optiska fibrer användes för flertalet av de experimentella studierna av två skäl; för det första är fotokänsligheten i fibrer större och dessutom vet man mindre om bakomliggande mekanismer jämfört med motsvarande bulk glas, och för det andra kan fibrer vara enklare att studera eftersom de experimentellt kan ses som en endimensionell struktur.Inledningsvis utfördes ablaherings experiment på bulk glas med en infraröd laser med pikosekund pulser. Raka kanaler med ett designtvärsnitt på 40x40 μm tillverkades på ovansidan (mot infallande ljus) och bottensidan av provet och de resulterande geometrierna analyserades. Resultaten visar en högre känslighet för variationer i experimentella parametrar vid ablahering på undersidan vilket kan förklaras av inkubations effekter i materialet. Dessutom är den resulterande geometrin på ovansidan V-formad, oavsett experimentella parametrar, vilket kunde relateras till den numeriska aperturen hos den fokuserande linsen, vilket förklaras av skuggningseffekter.Efter detta arbete flyttades fokus mot optiska fibrer, UV inducerade fiber Bragg gitter (FBG), och termisk bearbetning med konventionell ugn samt även med en CO2-laser som källa för strålningsvärme.Först konstruerades ett system för CO2-laservärmning av fibrer. För mätning av temperaturen hos bearbetade fibrer användes en speciell sorts FBG med hög temperaturstabilitet, kallade ”Chemical Composition Gratings” (CCG). En grundlig karaktärisering och temperaturkalibrering utfördes och temperaturdynamiken mättes med en tidsupplösning på under en millisekund. Temperaturprofilen i fibern, och laserns strålprofil, kunde mätas med en spatiell upplösning begränsad av gitterlängden och fiberns diameter. Temperaturer upp till ~1750 °C, vilket är högre än mjukpunktstemperaturen, kunde mätas med korresponderande uppvärmnings- och avsvalningshastighet på 10.500 K/s och 6.500 K/s.Därefter gjordes en omfattande undersökning av värmebearbetning och termisk regenerering av FBG:er i telekomfiber. Resultaten visar att termisk gitter-regenerering aktiveras av flera olika mekanismer. Värmebearbetning vid en temperatur omkring 900 °C resulterade i starka gitter efter en regenerering vid en temperatur på 1100 °C. Två olika aktiveringsenergier kunde extraheras från en Arrhenius plot avseende brytningsindexmodulation och Braggvåglängd, med en skärningspunkt tillika runt 900 °C, vilket indikerar en avvägning mellan två motverkande mekanismer vid denna temperatur.Slutligen undersöktes temperaturdynamiken och de spektrala egenskaperna under tillverkning av långperiodiga fibergitter (LPG). Gittren tillverkades med CO2-vi iilasersystemet genom att skapa en periodisk urgröpning medelst termisk ablahering. Transmissionsförluster kunde reduceras med noggrant valda processparametrar. Dessa parametrar identifierades genom mätningar av ablaherat djup och transmissionsförlust som funktion av laserintensitet och exponeringstid.
QC 20150924
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Zhang, Jingyu. "Polarization sensitive ultrafast laser material processing." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/419400/.
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In this thesis, I will concentrate on ultrafast laser interactions with various materials such as fused silica, crystalline silicon, amorphous silicon and nonlinear crystal. The first polarization sensitive ultrafast laser material interaction to be illustrated was second harmonic generation in lithium niobate by tightly focused cylindrical vector beams. The generated second harmonic patterns were experimentally demonstrated and theoretically explained. Existence of the longitudinal component of the fundamental light field was proven. The same beams were used for modifying fused silica glass. Distribution of the electric field in the focal region was visualized by the presence of self-assembled nanogratings. Also in this experiment, crystalline and amorphous silicon were modified by the focused cylindrical vector beams. The generated modifications matched well with the theoretical simulations. Polarization dependent structure was not observed under single pulse irradiation above the silicon surface. The generated isotropic crater structures with their smooth surface can be implemented as a wavefront sensor. Unexpectedly, an entirely different modification was observed after the double pulse laser irradiation. The size and orientation of the structure can be independently manipulated by the energy of the first pulse and polarization of the second pulse. Theoretical analysis was conducted and the formation mechanism of the polarization dependent structures was explained. This structure on silicon surface can be used for the polarization-multiplexed optical memory. One type of polarization sensitive ultrafast laser modification in fused silica is nanogratings. This modification exhibits form birefringence and therefore can be implemented for multi-dimensional optical data storage. Optimized data recording parameters were determined by sets of experiments. Stress-induced birefringence was observed and explained by material expansion at different conditions. Finally, the multilevel encoding of polarization and intensity states of light with self-assembled nanostructures was illustrated. A new writing setup was designed and involved a spatial light modulator, a half-wave plate matrix and a 4F optical system. The data recording rate was increased by 2 orders of magnitude compared to conventional laser direct writing setup using polarization optics. The recording and readout of digital information was experimental demonstrated. We successfully recorded across three layers a digital copy of a 310KB file. The benefits of 5D optical data storage, such as long lifetime and high capacity were illustrated. In addition, the theoretical limitations of the current writing system and readout system were discussed and several upgraded systems were proposed.
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Collins, Gustina B. "Laser Processing of Polyimide on Copper." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/32559.
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While work using a laser for processing a polymer dielectric is currently being studied, the purpose of this thesis is to present an effective and economical approach using laboratory equipment that is most commonly used and available for the processing of materials including polymers and metals. The use of a laser allows for a more cost effective and flexible method for processing polyimide over other wet and dry processes.
This thesis represents the results of research on the laser processing of polyimide on copper. The research examines the effect of the laser processing parameters using a CO2 laser. The parameters examined include the pulse width, repetition rate, and number of pulses. The processed samples include freestanding Kapton with no adhesive layer, freestanding Kapton with an adhesive layer, and Kapton with adhesive layered on copper. The laser processing used a single laser shot with the parameters being varied over a series of shots fired. The effect of the parameters was observed over large and small ranges. The characteristics of processed freestanding samples were graphically presented along with captured images. The results demonstrate that the laser processing of polyimide is strongly dependent on the laser pulse width and that the optimum value from these experiments suggest the use of a pulse width of 60ms for using a CO2 laser. From these results, further considerations for the laser processing of polyimide on copper were given.Master of Science
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Franzel, Louis. "Modification of Nanostructures via Laser Processing." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3024.
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Modification of nanostructures via laser processing is of great interest for a wide range of applications such as aerospace and the storage of nuclear waste. The primary goal of this dissertation is to improve the understanding of nanostructures through two primary routes: the modification of aerogels and pulsed laser ablation in ethanol. A new class of materials, patterned aerogels, was fabricated by photopolymerizing selected regions of homogeneous aerogel monoliths using visible light. The characterization and fabrication of functionally graded, cellular and compositionally anisotropic aerogels and ceramics is discussed. Visible light was utilized due to it’s minimal absorption and scattering by organic molecules and oxide nanoparticles within wet gels. This allowed for the fabrication of deeply penetrating, well resolved patterns. Similarly, nanoporous monoliths with a typical aerogel core and a mechanically robust exterior ceramic layer were synthesized from silica aerogels cross-linked with polyacrylonitrile. Simple variations of the exposure geometry allowed fabrication of a wide variety of anisotropic materials without requiring layering or bonding. Nanoparticle solutions were prepared by laser ablation of metal foils (Fe and Mo) in ethanol. Ablation of Fe generated Fe3O4 and Fe3C nanoparticles which were superparamagnetic with a saturation magnetization Ms = 124 emu/g. Zero field cooled (ZFC) measurements collected at an applied field of 50 Oe displayed a maximum magnetic susceptibility at 120 K with a broad distribution. Field cooled (FC) measurements showed a thermal hysteresis indicative of temperature dependent magnetic viscosity. Pulsed laser ablation of a Mo foil in ethanol generated inhomogeneous nanoparticles where Mo and MoC coexisted within the same aggregate. Formation of these unique nanoparticles is likely due to phase separation that occurs when a high temperature carbide phase cools after the laser pulse terminates. Similarly, magnetic nanoparticle suspensions were generated by pulsed laser ablation of Fe and Mo in ethanol. The formation of several carbide phases with no discernable alloy formation was seen. A decrease in magnetization with a decrease in Fe concentration was seen which was reconciled with the decreased Fe content in the system. However, at Fe concentrations below ~ 40%, an increase in Ms and Hc was observed which was reconciled with the disappearance of the ε–Fe3C. TEM analysis showed the formation of core-shell nanoparticles and Energy Filtered TEM showed the distribution of Fe-based nanoparticles in the suspensions.
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Harlan, Nicole Renee. "Titanium processing using selective laser sintering /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Musaev, Omar Wróbel Jerzy. "UV laser assisted processing of InP at different ambient conditions with variable number of pulses and fluences." Diss., UMK access, 2006.
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Thesis (Ph. D.)--Dept. of Physics and School of Computing and Engineering. University of Missouri--Kansas City, 2006."A dissertation in physics and telecommunications networking." Advisor: Jerzy Wrobel. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Nov. 1, 2007. Includes bibliographical references (leaves 185-190). Online version of the print edition.
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Choi, Hae Woon. "Femtosecond laser material processing for micro-/nano-scale fabrication and biomedical applications." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1184883900.
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Stoian, Razvan. "Adaptive techniques for ultrafast laser material processing." Habilitation à diriger des recherches, Université Jean Monnet - Saint-Etienne, 2008. http://tel.archives-ouvertes.fr/tel-00352662.
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Le besoin d'une très grande précision lors du traitement des matériaux par laser a fortement encouragé le développement des études de l'effet des impulsions ultra brèves pour la structuration des matériaux à une échelle micro et nano métrique. Une diffusion d'énergie minimale et une forte non linéarité de l'interaction permet un important confinement énergétique à des échelles les plus petites possibles. La possibilité d'introduire des changements de phases rapides et même de créer de nouveaux états de matière ayant des propriétés optimisées et des fonctions améliorées donne aux impulsions ultra brèves de sérieux arguments pour être utilisées dans des dispositifs très précis de transformation et de structuration des matériaux. L'étude de ces mécanismes de structuration et, en particulier, de leurs caractéristiques dynamiques, est une clé pour l'optimisation de l'interaction laser-matière suivant de nombreux critères utiles pour les procédés laser : efficacité, précision, qualité. Ce mémoire synthétise les travaux de l'auteur sur l'étude statique et dynamique du dépôt d'énergie ultra rapide, avec application aux procédés laser. La connaissance de la réponse dynamique des matériaux après irradiation laser ultra brève montre que les temps de relaxation pilotent l'interaction lumière-matière. Il est alors possible d'adapter l'énergie déposée à la réponse du matériau en utilisant les toutes récentes techniques de mise en forme spatio temporelle de faisceaux. Un couplage optimal de l'énergie donne la possibilité d'orienter la réponse du matériau vers un résultat recherché, offrant une grande flexibilité de contrôle des procédés et, sans doute, la première étape du développement de procédés « intelligents ».
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Arildsson, Mikael. "Origin and processing of laser doppler spectra /." Linköping : Univ, 2000. http://www.bibl.liu.se/liupubl/disp/disp2000/tek644s.pdf.
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James, Craig William. "Laser transfer processing of functional ceramic films." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589013.
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The incorporation of ferroelectric films, traditionally fabricated at high temperatures, with modern low temperature substrates has been an ongoing issue for the electroceramic community in recent years. The majority of ferroelectric film fabrication techniques utilise high temperature processing, with required temperatures ranging from 550-700 DC, for the production of thin films, to ",900-1200 DC, for thick films and bulk ceramics, with some fiuxes allowing fabrication at 850 DC. Some lead free electroceramics require processing at even higher temperatures. The limit of thermal stability for the majority of desired substrates lies significantly lower than these required processing temperatures. Platinised silicon has been shown to stable to maximum temperatures of 750 DC, with polymer and many semi-conductor substrates effective only from 150-350 DC. Clearly, direct deposition of ferroelectric films onto these family of substrates can not be realised at this time. Laser transfer processing (LTP) has recently been shown to be a viable alternative approach to these integration challenges. Films are initially fabricated on substrates stable to high temperatures (commonly single crystal sapphire), before bonding to low temperature, electrically useful substrates. The fabrication substrate is then removed by using a UV laser pulse to seperate the film and original substrate. In this thesis, lead zirconate titanate (PZT) thin films have been produced from a sol- gel technique. Thick-films have been deposited by spin coating a hybrid particle sol-gel slurry and by a conventional tap-casting route. The films were then transferred to a second substrate, usually platinised silicon but polymer-based substrates were also examined, using a KrF excimer laser (248 nm wavelength) to delaminate the films from the sapphire fabrication substrate. A primary aim was to understand the effects of LTP on interfacial structure and the electrical properties of the film samples.
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Ramme, Mark. "Ultrafast Laser Material Processing For Photonic Applications." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5846.
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Femtosecond Laser Direct Writing (FLDW) is a viable technique for producing photonic devices in bulk materials. This novel manufacturing technique is versatile due to its full 3D fabrication capability. Typically, the only requirement for this process is that the base material must be transparent to the laser wavelength. The modification process itself is based on non-linear energy absorption of laser light within the focal volume of the incident beam. This thesis addresses the feasibility of this technique for introducing photonic structures into novel dielectric materials. Additionally, this work provides a deeper understanding of the light-matter interaction mechanism occurring at high pulse repetition rates. A novel structure on the sample surface in the form of nano-fibers was observed when the bulk material was irradiated with high repetition rate pulse trains. To utilize the advantages of the FLDW technique even further, a transfer of the technology from dielectric to semiconductor materials is investigated. However, this demands detailed insight of the absorption and modification processes themselves. Experiments and the results suggested that non-linear absorption, specifically avalanche ionization, is the limiting factor inhibiting the application of FLDW to bulk semiconductors with today's laser sources.Ph.D.
Doctorate
Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering
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Moorhouse, Colin. "Laser processing of printed circuit board materials." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/195.
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Al-Waidh, Aos. "Manufacture of metamaterials using laser processing techniques." Thesis, Liverpool John Moores University, 2016. http://researchonline.ljmu.ac.uk/4455/.
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Denning, Paul Michael. "High power laser surface processing of hydroxyapatite." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399182.
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Sun, Yunlong. "Laser processing optimization for semiconductor based devices /." Full text open access at:, 1997. http://content.ohsu.edu/u?/etd,3.
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Yusoff, Nukman bin. "A study on laser processing of wood." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/35072.
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The carbon dioxide (CO2) laser woodcutting has been used as an alternative to traditional wood machining processes. Smaller kerf width and non-contact machining were among the advantages and unique features of laser woodcutting. On the other hand, conventional wood machining such as sawing involves the application of force to separate chips from the workpiece until the desired size of workpiece is achieved. The focus of this research is to study and identify the quality of CO2 laser woodcutting. Various species of Malaysian wood have been used for this study. The initial experiment was carried out by studying the dimensional accuracy and material removal rate which reveals the trend of the laser woodcutting process.
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Gross, Markus Sebastian. "Transient numerical simulation of laser materials processing with focus on laser cutting." Thesis, Heriot-Watt University, 2004. http://hdl.handle.net/10399/1119.
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Kuang, Zheng. "Parallel diffractive multi-beam ultrafast laser micro-processing." Thesis, University of Liverpool, 2011. http://livrepository.liverpool.ac.uk/1333/.
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During the last decade, ultrashort pulse lasers have been employed for high precision surface micro-structuring of materials such as metals, semiconductors and dielectrics with little thermal damage. Due to the ultra high intensity of focussed femtosecond pulses (I > 1012W/cm2), nonlinear absorption can be induced at the focus leading to highly localised material ablation or modification. This is now opening up applications ranging from integrated optics, through multi-photon induced refractive index engineering to precision surface modification for silicon scribing and solar cell fabrication. To ensure non thermal material processing, the input fluence (F) of the ultrashort pulse laser must be kept in the low regime (F ∼ 1Jcm-2), a few times above the well defined ablation threshold. Accordingly, μJ (10-6J) level pulse energy input is often required for ultrashort pulse laser fine micro/nano-surface structuring. Running at one kilohertz repetition rate, many current ultrashort pulse laser systems can provide mJ (10-3J) level output pulse energy. Accordingly, significant attenuation of the laser output is required for many applications and hence causes a great deal of energy loss. With this limitation in mind, holographic multiple beam ultrashort pulse laser processing, where the mJ pulse energy is split into many desired diffracted beams with arbitrary geometric arrangement, is proposed in this thesis. The multi-beam patterns are generated by phase modulation using computer generated holograms (CGHs) which are displayed on a Spatial Light Modulator (SLM). The ability to address these devices in real time and synchronize with scanning methods adds an additional flexibility to the processing. The results obtained in this thesis demonstrate high precision micro-fabrication of different kinds of materials with greatly increased processing efficiency and throughput, showing many potential industrial applications.
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Fox, Mahlen David Thomas. "Control and monitoring techniques for laser materials processing." Thesis, Heriot-Watt University, 2002. http://hdl.handle.net/10399/398.
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Soib, Bin Selamat Mohmad. "Laser surface processing of Ti-6Al-4V alloy." Thesis, University of Strathclyde, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366777.
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Lobo, Leon M. "Solid phase by-products of laser material processing." Thesis, Loughborough University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272931.
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Erk, Patrick P. (Patrick Peter). "Digital signal processing techniques for laser-doppler anemometry." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/43026.
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Martinez-Jimenez, Gregorio. "Laser processing of amorphous silicon for photonic applications." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/415853/.
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The topic of the research that is presented in this thesis is the development of a laser-based method for the crystallization of amorphous silicon (a-Si) films, deposited on various planar substrates for the fabrication of photonic structures. The emphasis is on lithium niobate which has many useful properties for photonic applications. This research stems from experimental evidence suggesting that it is possible to produce large Si crystallites by irradiating a-Si with continuous wave laser beams at visible wavelengths. This method has been particularly successful in semiconductor core optical fibres. Here this laser-crystallization method is being extended to planar geometries staring with glass substrates and extending to crystalline lithium niobate. The aim is to produce hybrid optoelectronic devices that will benefit from the properties of the constituents (Si and lithium niobate). These devices will target photonic applications in the area of optical telecommunications and sensing.
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Kamil, Ahmad. "Post processing for nylon 12 laser sintered components." Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3480.
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This research investigates the effect of post-processing on the mechanical characteristics and behaviour of laser sintered components produced by selective laser sintering (SLS). It aims to understand the material’s behaviour and to develop postprocessing methods that can be used to improve and maintain consistency in the mechanical properties of the layer manufactured material. Duraform Polyamide (Nylon 12) and a Sinterstation VanguardTM SLS machine were used to produce test specimens. The behaviour of the layer material characteristics was established using different fabrication orientations and tensile, compression, shear and flexure tests as benchmarking investigations. The results show that there are significant variations in mechanical properties, as well as divergences from previous results. In addition, section thickness in closed and open hollow structures was investigated in order to establish its effect on mechanical properties. The larger a sintered area, the greater the tensile properties gained when there is an increase of section thickness and when solid specimens are used. Moreover, when fill and outline scanning strategies were implemented in producing the specimens, the improvements were obtained in the tensile properties of nylon 12 laser-sintered material with no impact on geometry. To further improve the mechanical properties, a new post processing method that included heat treatment in air and vacuum environments was investigated. Experiments were conducted in air from room temperature to 140oC with a treatment time of 120 minutes and vacuum heat treatment was conducted from room temperature to 180oC with 16 hours and 100 hours treatment time. The material properties in both conditions were then analysed in terms of tensile properties, thermal characterisations, microstructure and geometrical changes. Heat treatment in air showed no significant improvement in mechanical properties. However, Nylon 12 SLS material heat-treated in a vacuum showed considerable improvement in crystallinity and peak melting point. Heat treatment for a longer period to approach the melting point, especially on material with the different section thicknesses and solid specimens and particularly in a vacuum, has a greater impact on mechanical properties, but this may not be sufficient to justify the cost and time involved.
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Oliveira, Uazir Orion Bezerra de. "Laser treatment of alloys: processing, microstructure and structural properties." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2007. http://irs.ub.rug.nl/ppn/298999803.
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Miroshnikova, Natalia. "Investigation of laser drilling processing using Speckle Correlation techniques." Licentiate thesis, Luleå, 2004. http://epubl.luth.se/1402-1757/2004/030.
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Nguyen, Hoang Cuong. "High speed processing for laser doppler blood flow imaging." Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517694.
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England, James Mark Carson. "In situ laser reflectometry of thermal processing of silicon." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239256.
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Bailey, Eric Stanton. "Sparse Frequency Laser Radar Signal Modeling and Doppler Processing." University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1271937372.
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Sun, Hongqing. "Microstructure Evolution of Bulk Metallic Glasses via Laser Processing." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1287025216.
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Allegre, Olivier. "Advanced polarization control for optimizing ultrafast laser micro-processing." Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/11793/.
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The ability to control and manipulate the state of polarization of a laser beam is becoming an increasingly desirable feature in a number of industrial laser micro-processing applications. Being able to control polarization would enable the improvement of the efficiency and quality of processes such as the drilling of holes for fuel-injection nozzles, the processing of silicon wafers or the machining of medical stent devices. This thesis presents novel, liquid-crystal-based optical setups for controlling the polarization of ultrafast laser beams, and demonstrates how such optical setups can be used to improve laser micro-processing efficiency and quality. Two experimental strategies were followed: the first used dynamic control of the polarization direction of a linearly polarized beam; the second generated beams with complex polarization structures. Novel optical analysis methods were used to map the polarization structures in the focal region of these laser micro-processing setups, using Laser Induced Periodic Surface Structures (LIPSS) produced on stainless steel sample surfaces at low laser fluence (around 1.5J/cm²), close to the ablation threshold of steel (i.e. 0.16J/cm²). This helped to characterize and calibrate the optical setups used in this thesis. The first experimental method used a fast-response, analogue, liquid-crystal polarization rotation device to dynamically control the direction of linear polarization of a laser beam during micro-processing. Thanks to its flexibility, the polarization rotator could be set-up in various synchronized configurations, for example keeping the polarization direction constantly perpendicular to the beam scanning motion. Drilling and cutting tests were performed on thin (~0.4mm thick) stainless steel sheets using a 775nm femtosecond laser at 24J/cm². The experimental results showed a consistent improvement in the micro-processing quality when the polarization direction was synchronized with the beam scanning motion. The sidewall surface roughness and edge quality of the machined structures were improved significantly, with the dimensions of ripples and distortions divided by a factor of two. The overall processing efficiency was also increased compared to that produced by linear or circular polarizations. The second experimental method used a digital, Liquid-Crystal On Silicon (LCOS) Spatial Light Modulator (SLM) to generate polarization structures with a cylindrical geometry, or Cylindrical Vector Beams (CVBs). A Jones matrix analysis was used to model the optical setup and predict the ability to produce CVBs in this way. The setup was implemented in a 775nm femtosecond laser micro-processing bench and the resulting polarization analyzed with a polarizing filter, demonstrating a polarization purity better than 84%. The amplitude and polarization properties in the focal region of the setup were studied using LIPSS produced on the surface of stainless steel samples at low fluence (1.5J/cm²), to check that the expected state of polarization had been achieved. An analytical model of the experimental setup was developed to explain the experimental results. The model predictions were in agreement with the experimental results and clarified how the polarization and phase structures affect the focal properties of the produced laser beams. Various types of CVBs were used with a high laser beam fluence (24J/cm²) for micro-machining 0.2-0.4mm thick stainless steel plates. A comparative analysis of micro-machining with radially, azimuthally, circularly and linearly polarized beams was carried out. It was shown that a radially polarized beam was more efficient at drilling and cutting high-aspect-ratio features when the plate thickness was above 0.2mm. The gain in processing speed was better than 5% compared with a circularly polarized beam and better than 10% compared with an azimuthally polarized beam, under the chosen processing parameters. However the processing speed was similar for all these polarization states (radial, azimuthal and circular) when machining 0.2mm thick plates. It was also shown that a radially polarized beam improved the processing quality, reducing the distortions affecting the edge quality of the machined structures.
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Chen, Xiaoming. "Laser-cluster interaction and its applications in semiconductor processing /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Teppitaksak, Achaya. "Advanced laser sources for industrial processing and remote sensing." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/46040.
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In the fifty years since their discovery, the use of laser oscillators and amplifiers has increased to cover a wide range of applications. This thesis develops diode-pumped solid-state (DPSS) lasers for two main applications: industrial processing and remote sensing. The first half of this thesis investigates the development of bounce geometry lasers that can be used to generate high power light sources suitable for industrial processing using diode-pumped Nd:YVO4 laser sources at both 1342nm and 1064nm transitions. The first of these investigations develops bounce geometry configuration Nd:YVO4 laser sources operating at 1342nm. For continuous wave (CW) operation at powers of 15.9W with 30% optical-to-optical efficiency were achieved. For pulsed operation, Q-switching based on an acousto-optic modulator and mode-locking based on nonlinear-mirror mode-locking were demonstrated. To suit a range of different industrial applications, a versatile gain switched laser diode source at a wavelength of 1064nm was developed to have independently adjustable pulse energies, pulse duration and repetition rates. To reach a commercially useful power level, a seed laser was amplified in a master oscillator power amplifier (MOPA) configuration using two ultrahigh-gain Nd:YVO4 bounce amplifiers in series. In a first amplifier (preamplifier), a small-signal gain of ~50dB with good TEM00 beam quality preservation was achieved with 24W pumping while a second power amplifier was used to achieve an average output power of up to ~14W using an input seed power of 188mW. The second part of this thesis develops laser sources for remote sensing applications based on direct diode pumping of Alexandrite lasers in an end-pumping configuration. When compared to Q-switched Nd:YAG lasers, which are typically used for satellite based remote sensing, Alexandrite lasers have the potential to be more efficient and offer more flexible wavelength tunability. Following a broad overview of Alexandrite lasers, this thesis investigates diode-pumped Alexandrite laser performance. To achieve a high average power, a compact laser cavity was built with output power as high as 26.2W and slope efficiency of 49%. This was more than an order of magnitude higher than previously reported from diode pumped Alexandrite lasers. To achieve TEM00 laser output, many extended cavity designs were investigated. Following this, to enhance the laser efficiency, an Alexandrite laser was developed utilizing the unique characteristics of temperature-dependent gain of Alexandrite and the performance from 20-150˚C was characterised. To demonstrate high pulse energies, suitable for remote sensing applications, for the first time, a direct diode pumping Q-switched Alexandrite was demonstrated. A Q-switched output pulse energy of >1mJ at 100Hz pulse repetition rate in TEM00 mode was achieved.
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Li, Kun. "Laser micro-processing of silicon using nanosecond pulse shaped fibre laser at 1 μm wavelength." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/245313.
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Processing of Si in the semiconductor and solar cell industry has been dominated by the Diode Pumped Solid State (DPSS) Ultraviolet (UV) laser. Recent advances in laser source technology have produced fibre lasers with Master Oscillator Power Amplifier (MOPA) architectures that offer high repetition rates, high operational efficiencies, and pulse modulation controls exceeding those of typical Q-switched DPSS lasers. The aim of this research is to investigate 1 μm fibre laser machining of Si with a view to identifying the influential laser parameters for optimum processing of high quality, high efficiency micro drilling and surface texturing applications. A secondary aim is to develop a greater understanding of the laser material interactions and material removal mechanism when using fast rise-time nanosecond laser pulse envelopes. The IR fibre laser was able to perform percussion drilling and single pulse machining on the polished Si over a range of intensities up to 1.22 GW/cm2. With the optimum parameters, the micro-sized holes generated by the IR laser have a well defined edge, no heavy recast and no cracks. With a pulse shape of fast rise time (<7.5 ns for a 10-90% rise in signal), a high front peak power zone (approaching 14 kW) and an energetic long tail (40-180 ns), the absorption coefficient of Si at IR wavelength increased dramatically with time and temperature due to the fact that the liquid Si has a metal like absorption behavior. As a result, Si was quickly melted and the rest of pulse energy was able to remove the liquid Si effectively. The machining process left a limited amount of resolidified melt droplets and vapor condensates, which could be washed off ultrasonically. The drilling process was energy efficient when melt expulsion dominated the machining mechanism (0.08-0.2 mJ pulse energy depending on the pulse durations). The low energy pulse (~0.2 mJ) can achieve similar depth as the high energy pulse (~0.7 mJ), so high repetition rates of 100 kHz can be used to instead of 25 kHz, resulted in high processing speed. In addition, by comparing the single pulse machining with the state of the art UV laser, the IR fibre laser machined deeper features and better surface finish in the pulse energy region of >0.07 mJ. With the pulse shaping capability, the material properties can be varied and the wavelength factor can be minimized. The results suggest that applications like microvia drilling can now be carried out with the more flexible and low cost IR fibre laser. The increased repetition rates of fibre laser can increase production speed to satisfy the needs of drilling ~10 thousands holes per second, required by the modern semiconductor and solar cell production. The shortened optical penetration length of 1 μm wavelength laser on Si with increasing temperature and sufficient thermal diffusion length resulted from the asymmetrical fibre laser pulse and the dynamic properties of Si produced a thick liquid layer. A one-dimensional heat conduction model based on the surface heating source predicted that this superheated liquid layer was able to stay above 4706 K (0.905 times the thermal critical temperature 5200 K of Si) for longer than 70 ns to induce explosive boiling. This proposed material removal mechanism was also confirmed by the shadowgraph images, showing particulates ejection lasting up to ten microseconds after the laser pulse. The estimated hole depth based on the explosive boiling alone were different from the measured ones at varying peak power densities (<1.22 GW/cm2) but fixed pulse duration (200 ns), since Si was removed by a mixture of mechanisms. With varying pulse durations (40-200 ns) but fixed peak power density (~0.63 GW/cm2), the estimated depth based on the explosive boiling was in close agreement with the measured ones (6% difference on average). The SEM images at this power density showed a micron- /submicron-sized debris field, which was also observed with the explosive boiling in the past. Although the improved quality of Si machining was demonstrated with the 1 μm MOPA based fibre laser, the setup of this system was only applicable to surface texturing, blind holes and through holes of less than 100 μm in depth. Further research is required to demonstrate the capability of more energetic pulse with higher peak power and large pulse duration range to explore more machining options.
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Cevikbas, Orcun. "Data Acquisition And Processing Interface Development For 3d Laser Rangefinder." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607514/index.pdf.
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In this study, it is aimed to improve the previously developed data acquisition program which was run under DOS and 2D surface reconstruction program under Windows. A new system is set up and both data acquisition and processing software are developed to collect and process data within just one application, running under Windows.
The main goal of the thesis is to acquire and process the range data taken from the laser rangefinder in order to construct the 3D image map of simple objects in different positions for indoor environments.
The data acquisition program collects data in helical way. To do this, appropriate parameters for the data acquisition interface are determined. In the data processing step, it is aimed to use basic triangulation algorithms and threshold conditions to calculate resolutions, detect noisy points and segment objects from the environment for line fitting.
The developed and implemented data acquisition and processing interfaces in the thesis are capable of creating 3D image map and obtaining the view of scanned environment in a short time with high accuracy.
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Itoh, Sho. "Studies on laser processing of glasses for micro- and nanostructures." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217174.
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Sharp, Martin Charles. "Mathematical modelling of continuous wave CO2 laser processing of materials." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38157.
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Gečys, Paulius. "Ultrashort pulsed laser processing of thin-films for solar cells." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121001_093555-45841.
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Present PhD thesis is the experimental and theoretical analysis of thin layer ultrashort pulsed laser ablation processes for photovoltaic devices. Experimental work was supported by modeling and simulation of energy coupling and dissipation inside the layers. The absorbed laser energy was transformed to localized transient heating inside the structure. Selectiveness of the ablation process was defined by optical and mechanical properties of the materials, and selection of the laser wavelength facilitated control of the structuring process. The 1064 nm wavelength was found optimal for the CIGS solar cell scribing in terms of quality and process speed. It is very positive result for industrial applications as the cost and the system complexity are decreased. The solar cell efficiency test revealed minor degradation in photo-electrical efficiency after the laser scribing was applied to the solar cell samples. Lock-in thermography measurements did not revealed any internal shunt formation during laser scribing with picosecond pulse duration. Picosecond lasers with fundamental harmonics and high repetition rates can be used to accomplish efficient and fast scribing process which is able to fit the demands for industrial solar cell scribing applications.Disertacijos darbo tikslas buvo, modeliuojant bei vykdant eksperimentus, suprasti plonų sluoksnių, naudojamų Saulės elementuose, abliacijos procesus ultratrumpais impulsais, siekiant juos pritaikyti integruotų jungčių fotovoltiniuose moduliuose formavimui. Eksperimento rezultatams pagrysti buvo vykdomas lazerio spinduliuotės sklidimo bei pasiskirstymo plonasluoksnėje Saulės elemento struktūroje modeliavimas. Sugerta lazerio energija lokaliai užkaitiną medžiagą. Kadangi lazerinio proceso selektyvumas priklauso nuo medžiagos optinių savybių, todėl yra itin svarbu parinkti tinkamą lazerio spinduliuotės bangos ilgį, norint sukaupti spinduliuotę reikiamame plonasluoksnės struktūros sluoksnyje. Nustatyta, kad fundamentinė pikosekundinio lazerio spinduliuotė (1064 nm) yra optimaliausia P3 tipo rėžio formavimui CIGS Saulės elemente. Pramonės taikymams tai yra itin svarbu, nes tokiu atveju mažėja industrinės lazerinės sistemos sudėtingumas bei kaina. Saulės elementų efektyvumo tyrimai parodė nežymų fotoelektrinio efektyvumo sumažėjimą po lazerinio apdirbimo ultra trumpais impulsais, tačiau nebuvo užfiksuota defektų generacijos lazeriais paveiktose kanalo kraštų zonose. Disertacijoje pasiūlyti ir išbandyti pluošto formavimo ir lygiagretaus sluoksnių raižymo metodai, didinantys proceso našumą ir raižymo kokybę. Pikosekundiniai, didelio impulsų pasikartojimo dažnio lazeriai gali būti panaudoti didelės spartos bei aukštos kokybės Saulės elementų raižymo procesuose.
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Wagner, Franz X. "Excimer laser ablation and processing of II-VI compound semiconductors." Thesis, University of Hull, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363271.
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Shakeel, Safdar. "Effects of non-conventional beam geometries in laser materials processing." Thesis, University of Manchester, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545860.
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The way the temperature is distributed inside the material is of prime importance in laser materials processing. Optimisation of different laser processes requires control over the temperature distribution in order to control microstructure and residual stressesb y manipulating heating/cooling rates and thermal gradients. Currently most of the laser material processing is carried out by either circular or rectangular beam geometry with variation in temperature distribution caused by either the variation of laser power, spot size or scanning speed. Variations in these parameters are often limited by other processing conditions, therefore the possibility of modifying the microstructure and residual stresses are limited. If any other parameter can be identified, such that variation of this parameter alone (i. e. without changing the laser power or scanning speed) can alter the temperature distribution, then it will provide added flexibility to the process control. One possible method of varying the temperature distribution, and hence the heating /cooling rates and thermal gradients is to modify the geometry of laser beams. The effect of laser beam geometry, particularly of non-conventional laser beam geometries on laser processing of materials has received very little attention. This thesis presents a detailed numerical investigation of the effects of non-conventional laser beam geometries on laser surface heating, laser transformation hardening, laser tube bending and laser melting of metallic materials. The numerical models have been validated by experiments using a diode laser. The temperature distributions, heating/cooling rates, thermal gradients, stress distributions and distortions were evaluated. The work presented in this thesis highlights the different attributes of conventional and non-conventional laser beam geometries. Laser beam geometries were found to influence heating and cooling rates as well as residual and normal stress distributions in materials processing. In particular, the donut beam results in transient bi-axial stress state which does not exist for any other solid beam geometry. These attributes can be utilised as an advantage not only in the investigated processes but could also be utilised for improving various other laser material processes
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Shokeen, Lalit. "Multiscale simulation of laser ablation and processing of semiconductor materials." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5495.
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We present a multiscale model of laser-solid interactions in silicon based on an empirical potential developed under conditions of strong electronic excitations. The parameters of the interatomic potential depends on the temperature of the electronic subsystem Te, which is directly related to the density of the electron-hole pairs and hence the number of broken bonds. We analyze the dynamics of this potential as a function of electronic temperature Te and lattice temperature Tion. The potential predicts phonon spectra in good agreement with finite-temperature density-functional theory (DFT), including the lattice instability induced by the high electronic excitations. For 25fs pulse, a wide range of fluence values is simulated resulting in heterogeneous melting, homogenous melting, and ablation. The results presented demonstrate that phase transitions can usually be described by ordinary thermal processes even when the electronic temperature Te is much greater than the lattice temperature TL during the transition. However, the evolution of the system and details of the phase transitions depend strongly on Te and corresponding density of broken bonds. For high enough laser fluence, homogeneous melting is followed by rapid expansion of the superheated liquid and ablation. Rapid expansion of the superheated liquid occurs partly due to the high pressures generated by a high density of broken bonds. As a result, the system is readily driven into the liquid-vapor coexistence region, which initiates phase explosion. The results strongly indicates that phase explosion, generally thought of as an ordinary thermal process, can occur even under strong non-equilibrium conditions when Te >>TL. In summary, a detailed investigation of laser-solid interactions in silicon is presented for femtosecond laser pulse that yields strong far-from-equilibrium conditions.Ph.D.
Doctorate
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Peters, Christopher N. D. "In process monitoring and control for Nd:YAG laser material processing." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399233.
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Gomez, S. "Laser induced fluorescence measurements in inductivity coupled of processing plasmas." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368755.
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Uzunsoy, Deniz. "Processing and characterisation of selective laser sintered (SLS) Rapidsteel TM." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411877.
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