Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 8
Book Description
Numerical Model of Laser Ablation and Plasma Expansion for Ultrashort Laser Pulses
Author: Numerical Simulations of Ultrashort Laser Pulse Ablation and Plasma Expansion in Ambient Air
Author: Kinetic and Hydrodynamic Simulations of Laser Ablation and Plasma Plume Expansion Induced by Bursts of Short Laser Pulses
Author: Omid A. RanjbarPublisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :
Book Description
Ablation of materials by nanosecond laser pulses involves expansion of a laser-induced vapor plume into a background gas. The absorption of the incident laser radiation by the plume can substantially decrease the amount of laser energy absorbed directly by the target, and, correspondingly, the amount of the ablated material. This plasma shielding effect limits the overall efficiency of industrial laser systems designed for material removal applications. The goal of the present work is to numerically study the expansion process of plumes induced by irradiation of a metal target by bursts or groups of nanosecond laser pulses and to reveal the implications of the interaction between plumes induced by individual pulses for the efficiency of material removal. The plume expansion induced by irradiation of a copper target in argon background gas is studied based on one- and two-dimensional hybrid computational models that include a hydrodynamic or kinetic model of plasma plumes. The hydrodynamic model is based on finite-difference solution of gas dynamics equations. The kinetic model is implemented in the form of the direct simulation Monte Carlo (DSMC) method. In this work, the generalization of the DSMC method for plasma flows is developed. The effects of laser fluence, spot size, inter-pulse separation, and background gas pressure are thoroughly studied. The numerical simulations of plume expansion induced by a burst of pulses indicate the formation of complicated flow structures with cascades of the primary and secondary shock waves and strong interaction between plumes induced by individual pulses. The simulations reveal the plume accumulation effect when the plumes induced by preceding pulses in a burst change conditions of propagation of plumes generated by subsequent pulses. The degree of plasma shielding increases with increasing number of laser pulses due to the plume accumulation effect. It results in reduction of the effectiveness of material removal by the subsequent pulses. The degrees of the plasma shielding and plume accumulation effects strongly depend on the inter-pulse separation and laser spot size. The trade-off between the plume accumulation and thermal accumulation effects maximizes the ablation depth per pulse at a certain value of the time delay between pulses.
Ultraviolet Femtosecond and Nanosecond Laser Ablation of Silicon
Author: Richard E. RussoPublisher:
ISBN:
Category :
Languages : en
Pages : 9
Book Description
Femtosecond laser ablation of silicon in air was studied and compared with nanosecond laser ablation at ultraviolet wavelength (266 nm). Laser ablation efficiency was studied by measuring crater depth as a function of pulse number. For the same number of laser pulses, the fs-ablated crater was about two times deeper than the ns-crater. The temperature and electron number density of the pulsed laser-induced plasma were determined from spectroscopic measurements. The electron number density and temperature of fs-pulse plasmas decreased faster than ns-pulse plasmas due to different energy deposition mechanisms. Images of the laser-induced plasma were obtained with femtosecond time-resolved laser shadowgraph imaging. Plasma expansion in both the perpendicular and the lateral directions to the laser beam were compared for femtosecond and nanosecond laser ablation.
Ultrafast dynamics of melting and ablation at large laser intensities
Author: Ilja MingareevPublisher: Cuvillier Verlag
ISBN: 3736928785
Category : Science
Languages : en
Pages : 158
Book Description
Diese Arbeit leistet einen Beitrag zum Verständnis der ultraschnellen Abtrags- und Schmelzphänomene von Festkörpern bei Anregung mit Laserstrahlung großer Intensität. Fundamentale Aspekte des laserinduzierten Abtrags von Reinmetallen (Au, Al, Cu, Fe, W) mit Ultrakurzpuls-Laserstrahlung wie z.B. Laser-Materie-Wechselwirkung, Plasmabildung, Verdampfung und Schmelzdynamik wurden untersucht. Darüber hinaus wurde Schmelzen und Schweißen von technischem Borosilikatglas mittels hochrepetierender Ultrakurzpuls-Laserstrahlung untersucht. Für Untersuchungen der transienten laserinduzierten Vorgänge auf unterschiedlichen Zeitskalen wurden neuartige experimentelle Verfahren entwickelt und eingesetzt. Pumpprobe Photographie wurde für zeitaufgelöste Messungen auf einem erweiterten zeitlichen Detektionsbereich bis ca. 2 Mikrosekunden mit Sub-Pikosekunden Auflösung realisiert. Für Detektion von transienten Brechungsindexmodifikationen und Morphologieänderungen wurde ein neuartiges, zeitaufgelöstes Verfahren zur quantitativen Phasenmikroskopie (TQPm) entwickelt. Die geometrischen und zeitlichen Profile der eingesetzten Laserstrahlung großer Intensität wurden beim Abtragen von Metallen untersucht. Aufheizung des Materials bedingt durch spontane verstärkte Emission mit Pulsdauer im Nanosekundenbereich führt zu einem materialabhängigen Temperaturanstieg von mehreren hundert Kelvin und wurde numerisch untersucht. Zeitaufgelöste Schattenphotographie und quantitative Messungen des Abtragsvolumens von Metallen wurden in unterschiedlichen Umgebungen durchgeführt. Im untersuchten zeitlichen Detektionsbereich kann die beobachtete Abtragsdynamik in mindestens vier charakteristischen Zeitregimes klassifiziert werden: Ausbreitung von dichtem Materialdampf und Plasma, Verdampfung aufgrund der Nukleationseffekte, Abtrag in Form von flüssigen Schmelzstrahlen und Erstarrung. Basierend auf experimentellen Ergebnissen wurde ein qualitatives Modell für laserinduzierten Abtrag von Metallen bei großen Strahlungsintensitäten aufgestellt, welches bedeutende Unterschiede zum Abtragen bei schwellennahen Intensitäten aufweist. Insbesondere sind physikalische Vorgänge die im Zusammenhang mit Materieüberhitzung stehen wie z.B. Phasenexplosion und “boiling crisis”, als entscheidende Abtragsphänomene suggeriert worden. Laserinduziertes Schmelzen von technischem Borosilikatglas mit hochrepetierender Ultrakurzpuls-Laserstrahlung wurde mittels TQPm zeitaufgelöst untersucht. Experimentelle Ergebnisse weisen transiente Brechungsindexmodifikationen auf welche auf Ionisationsprozesse und Verdichtung der Materie zurückzuführen sind. Als eine wichtige Anwendung dieser Prozesse wurde das Mikroschweißen von dünnen Glas- und Silizium-Platten demonstriert. Beim Schmelzen von Material an Substrat-Grenzflächen können konsistente Schweißnähte im Mikrometerbereich erzeugt werden.
Characteristics of Ultrafast Laser Produced Plasma and Its Application in Thin Film Deposition
Author: Zhiyu ZhangLaser Ablation and Its Applications
Author: Claude PhippsPublisher: Springer Science & Business Media
ISBN: 0387304525
Category : Science
Languages : en
Pages : 598
Book Description
Laser ablation describes the interaction of intense optical fields with matter, in which atoms are selectively driven off by thermal or nonthermal mechanisms. The field of laser ablation physics is advancing so rapidly that its principal results are seen only in specialized journals and conferences. This is the first book that combines the most recent results in this rapidly advancing field with authoritative treatment of laser ablation and its applications, including the physics of high-power laser-matter interaction. Many practical applications exist, ranging from inertial confinement fusion to propulsion of aerostats for pollution monitoring to laser ignition of hypersonic engines to laser cleaning nanoscale contaminants in high-volume computer hard drive manufacture to direct observation of the electronic or dissociative states in atoms and molecules, to studying the properties of materials during 200kbar shocks developed in 200fs. Selecting topics which are representative of such a broad field is difficult. Laser Ablation and its Applications emphasizes the wide range of these topics rather than - as is so often the case in advanced science – focusing on one specialty or discipline. The book is divided into four sections: theory and modeling, ultrafast interactions, material processing and laser-matter interaction in novel regimes. The latter range from MALDI to ICF, SNOM’s and femtosecond nanosurgery to laser space propulsion. The book arose from the SPIE series of High Power Laser Ablation Symposia which began in 1998. It is intended for a graduate course in laser interactions with plasmas and materials, but it should be accessible to anyone with a graduate degree in physics or engineering. It is also intended as a major reference work to familiarize scientists just entering the field with laser ablation and its applications.
Simulation of Laser-tissue Thermal Interaction and Plasma-mediated Ablation
Author: Jian JiaoPublisher:
ISBN:
Category : Laser ablation
Languages : en
Pages : 156
Book Description
In this dissertation, two types of laser-tissue interactions - ultra-short pulsed (USP) laser-tissue thermal interaction and plasma-mediated ablation - are numerically investigated. The thermal interaction is focused on laser hyperthermia skin cancer treatment. A combined ultrafast radiative transfer and bioheat transfer model is developed to predict the temperature distribution in a 2-D axisymmetric skin tissue cylinder subjected to a train of short pulsed irradiations. An appropriate mathematical model to describe the focused laser beam transport is considered. The laser propagation in the tissue is simulated via solving the transient equation of radiative transfer with the Transient Discrete-Ordinates Method. The bioheat transfer equation is calculated by the Alternative Directional Implicit Method. A numerical scheme is introduced to deal with the multi-time-scale heat transfer problems in a three-layer model skin tissue exposed to multiple short laser pulses. Parametric studies including influences of lens diameter, laser focused depth, wavelength and laser power on killing different types of skin tumors are carried out. For the study of USP laser induced plasma-mediated ablation in transparent media, an ionization rate equation is adopted, which consists of the multiphoton and avalanche ionizations, and diffusion and recombination effects. The present 2-D axisymmetric numerical model is validated via extensive comparisons with experimental measurements and other 1-D numerical models available in the literature. The dynamic process of plasma formation for ablation in pure water can be better visualized by the current modeling. To determine plasma-mediated ablation threshold, we propose that a certain number of free electrons are required to trigger the avalanche ionization. Based on this assumption, the ablation thresholds for pulse widths down to the femtoseconds range at wavelength 800 nm are calculated for transparent corneal epithelium. It is found that the critical seed free electron-density decreases as the pulse width increases, obeying a tp-5.65 rule. A complete numerical model with all ionization and loss mechanisms is also employed to elucidate and validate the conditions when avalanche ionization occurs and dominates in the plasma-mediated ablation process. Moreover, the crater sizes ablated in a PDMS by a 900 fs pulsed laser at wavelength 1552 nm are modeled using the present model, and the results match with the existing experimental measurements. The study of plasma-mediated ablation is further extended to turbid media. For ablation in absorbing and highly-scattering biological tissues, combined modeling of ultrafast radiative transfer and plasma formation is needed. We studied plasma-mediated ablation in a model human skin tissue, in which the rate equation is modified with chromophore ionization in addition to the multiphoton and avalanche ionizations. A parametric study on the influences of band gap, critical free-electron density and recombination rate on the prediction of ablation threshold in the model skin tissue is carried out. Moreover, investigation on crater formation is conducted, and the modeled crater sizes are compared with available experimental measurements on corundum and sapphire materials. For ablation in corundum and sapphire, the free electrons are generated via photoionization (multiphoton and tunneling ionizations) and avalanche ionization. The onset of mass ablation in the material is assumed when the local absorbed laser energy is sufficient to cause evaporation. Good agreements between the modeling and experiments are observed.
Laser Ablation
Author: Tatiana ItinaPublisher: BoD – Books on Demand
ISBN: 9535136992
Category : Science
Languages : en
Pages : 292
Book Description
Shortly after the demonstration of the first laser, the most intensely studied theoretical topics dealt with laser-matter interactions. Many experiments were undertaken to clarify the major ablation mechanisms. At the same time, numerous theoretical studies, both analytical and numerical, were proposed to describe these interactions. These studies paved the ways toward the development of numerous laser applications, ranging from laser micro- and nanomachining to material analysis, nanoparticle and nanostructure formation, thin-film deposition, etc. Recently, more and more promising novel fields of laser applications have appeared, including biomedicine, catalysis, photovoltaic cells, etc. This book intends to provide the reader with a comprehensive overview of the current state of the art in laser ablation, from its fundamental mechanisms to novel applications.
Laser Ablation and Desorption
Author: Publisher: Academic Press
ISBN: 0080860206
Category : Technology & Engineering
Languages : en
Pages : 671
Book Description
This volume introduces the subject of laser ablation and desorption to scientists and engineers. It covers fundamental experimental and theoretical tools, models, and techniques, and introduces the most important applications. Clearly written and organized in a straightforward manner, Laser Ablation and Desorption lead the reader straight through the fundamentals of laser-surface interactions. Each chapter is self-contained and includes references to other chapters as necessary, so that readers may begin with the topic of greatest interest and follow the references to other aspects of the subject contained within the book. Key Features * Provides up-to-date information about one of the most active fields in physics today * Written and edited by major figures in the field of laser ablation and desorption * Represents the most comprehensive treatment of the state-of-the-art available