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Texturização em superfícies de titânio grau 2 irradiadas com laser de pulsos ultracurtos / Texturing in titanium grade 2 surface irradiated with ultrashort pulse laserNogueira, Alessandro Francelino 10 February 2015 (has links)
A texturização por microusinagem a laser é uma importante alternativa para que se consiga melhorar a ligação de aderência entre materiais compósitos e o titânio, aplicados em componentes estruturais na indústria aeronáutica. A execução de texturização em chapas de titânio deve-se ao fato de que a técnica de junção preferida para muitos materiais compósitos é a ligação adesiva. Neste trabalho foram realizadas texturizações em chapas de titânio utilizando laser com pulsos ultracurtos de largura temporal da ordem de femtossegundos. Tal processo resultou em mínima transferência de calor para o material, evitando assim deformação superficial da chapa de titânio bem como a formação de material ressolidificado na região ablacionada. Estes inconvenientes ocorreram na utilização do laser chaveado com pulsos de nanossegundos. Foram executadas três tipos de texturizações utilizando laser com pulsos de femtossegundos, com variações nas distâncias entre as linhas usinadas. Pela análise das superfícies obtidas, detectou-se que a molhabilidade aumenta quando há o aumento da distância entre as linhas da texturização. Avançando nas análises, pela perfilometria óptica das superfícies texturizadas observou-se que há sensível aumento do volume disponível para penetração do adesivo estrutural quando são diminuídas as distâncias entre as linhas texturizadas. Nos ensaios de tração realizados observou-se que há o aumento da resistência ao cisalhamento da junta adesiva com a diminuição da distância entre as linhas texturizadas. / The texturing laser micromachining is an important alternative to improve the bonding adhesion between composites and titanium, which are applied to structural components in the aerospace industry. The texturing running on titanium plates is due to the fact that the preferred joining technique for many composite materials is the adhesive bonding. In this work, titanium plates were texturized using laser ultrashort pulses temporal widths of femtoseconds. This process resulted in minimal heat transfer to the material, avoiding deformation of the titanium plate surface as well as the formation of resolidified material in the ablated region. These drawbacks have occurred with the use of nanoseconds pulses. Were performed three types of texturing using laser with femtosecond pulses, with variations in the distances between the machined lines. The analysis of the obtained surfaces found that the wettability increases when there is the increased distance between the texturing lines. Advancing in the analysis by optical profilometry of textured surfaces was observed that there is substantial increase in the volume available for penetration of structural adhesive when the distances between the textured lines are diminished. In tensile tests conducted it was observed that there is an increase in shear strength of the adhesive joint by reducing the distance between the textured lines.
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Texturização em superfícies de titânio grau 2 irradiadas com laser de pulsos ultracurtos / Texturing in titanium grade 2 surface irradiated with ultrashort pulse laserAlessandro Francelino Nogueira 10 February 2015 (has links)
A texturização por microusinagem a laser é uma importante alternativa para que se consiga melhorar a ligação de aderência entre materiais compósitos e o titânio, aplicados em componentes estruturais na indústria aeronáutica. A execução de texturização em chapas de titânio deve-se ao fato de que a técnica de junção preferida para muitos materiais compósitos é a ligação adesiva. Neste trabalho foram realizadas texturizações em chapas de titânio utilizando laser com pulsos ultracurtos de largura temporal da ordem de femtossegundos. Tal processo resultou em mínima transferência de calor para o material, evitando assim deformação superficial da chapa de titânio bem como a formação de material ressolidificado na região ablacionada. Estes inconvenientes ocorreram na utilização do laser chaveado com pulsos de nanossegundos. Foram executadas três tipos de texturizações utilizando laser com pulsos de femtossegundos, com variações nas distâncias entre as linhas usinadas. Pela análise das superfícies obtidas, detectou-se que a molhabilidade aumenta quando há o aumento da distância entre as linhas da texturização. Avançando nas análises, pela perfilometria óptica das superfícies texturizadas observou-se que há sensível aumento do volume disponível para penetração do adesivo estrutural quando são diminuídas as distâncias entre as linhas texturizadas. Nos ensaios de tração realizados observou-se que há o aumento da resistência ao cisalhamento da junta adesiva com a diminuição da distância entre as linhas texturizadas. / The texturing laser micromachining is an important alternative to improve the bonding adhesion between composites and titanium, which are applied to structural components in the aerospace industry. The texturing running on titanium plates is due to the fact that the preferred joining technique for many composite materials is the adhesive bonding. In this work, titanium plates were texturized using laser ultrashort pulses temporal widths of femtoseconds. This process resulted in minimal heat transfer to the material, avoiding deformation of the titanium plate surface as well as the formation of resolidified material in the ablated region. These drawbacks have occurred with the use of nanoseconds pulses. Were performed three types of texturing using laser with femtosecond pulses, with variations in the distances between the machined lines. The analysis of the obtained surfaces found that the wettability increases when there is the increased distance between the texturing lines. Advancing in the analysis by optical profilometry of textured surfaces was observed that there is substantial increase in the volume available for penetration of structural adhesive when the distances between the textured lines are diminished. In tensile tests conducted it was observed that there is an increase in shear strength of the adhesive joint by reducing the distance between the textured lines.
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Optimizing Ultra-Broadband Microwave Radiation through Plasma Dynamics of USPL FilamentsThornton, Erin Ashley 07 1900 (has links)
Ultrashort pulse lasers focused in air result in plasma filaments that generate ultra-broadband secondary radiation that ranges from the megahertz to terahertz. The plasma currents responsible for the broadband radiation are the ponderomotive for the terahertz regime and the plasma wake surface wave (PWSW) for the gigahertz regime. Through experimental studies, I explore the optimization of microwave regime (1 - 67 GHz) of the spectrum. The experiments consider the effects of background gas and pressure in the filamentation region, pulse length of the laser, and wavelength of the laser on the plasma currents that produce the broadband radiated pulse. The results of the first experiment suggest that reduction of the electron-neutral collisions permits the growth of the PWSW and improve microwave amplitude. The second experiment demonstrates a growth in resulting microwave signal as a result of collisional processes driven by longer pulse durations. The final experiment demonstrates and order of magnitude increase in the microwave field amplitudes when the wavelength of a picosecond scale, terawatt class laser pulse is increased from 1.035 microns to 9.2 microns.
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Laser-induced surface structuring for electron cloud mitigation in particle acceleratorsBez, Elena 11 December 2024 (has links)
Die Bildung von Elektronenwolken durch die Multiplikation von Sekundärelektronen im Strahlrohr von Teilchenbeschleunigern kann während des Betriebs zu einer verringerten Leistung führen. Durch Ultrakurzpuls-Laserstrukturierung kann die Sekundärelektronenemission einer Oberfläche effizient reduziert werden. Im Rahmen dieser Arbeit wurde eine Lösung zur Unterdrückung der Elektronenvervielfachung durch Laserstrukturierung der aus Kupfer bestehenden Innenwände der Strahlrohre des Large Hadron Colliders (LHC) entwickelt, die technische Einschränkungen und Anforderungen an die Oberflächeneigenschaften und Vakuumkompatibilität erfüllt. Dafür wurden fundamentale Abhängigkeiten zwischen den Laserbearbeitungsparametern und den Oberflächeneigenschaften wie z.B. der Abtragstiefe, den oberflächenchemischen Eigenschaften, der Wiederablagerung von Partikeln und letztendlich der Sekundärelektronenausbeute (SEY) im Labormaßstab untersucht. Für die Behandlung der Rohrinnenflächen der Vakuumkammern wurde ein spezieller Aufbau verwendet, der aus einer Pikosekunden Laserquelle, einem Strahlkopplungssystem, einer 15 m langen Hohlkernfaser und einem Roboter besteht, der sich im Inneren des Strahlrohrs bewegt. Dieses System wurde im Rahmen dieser Arbeit in Betrieb genommen und kalibriert. Eine Behandlung bei
niedriger akkumulierter Fluenz in Stickstofffluss resultierte in „optimalen Oberflächeneigenschaften“, d.h. einer geringen Abtragstiefe (ca. 15 μm ), geringer Partikelbedeckung, einer Cu2O dominierten Oberfläche und einem SEY-Maximum von 1.4 nach der Reinigung, welches sich während der elektroneninduzierten Konditionierung zu 1 reduziert. Die 10 m langen Strahlrohre, die in den kryogen gekühlten Magnetaufbauten im LHC installiert sind, sollen mit einem Longitudinal-Scanning-Verfahren selektiv bearbeitet werden. Ein 3.1 m langes, laserbearbeitetes Strahlrohr wurde im LHC installiert, um die Methode bezüglich möglicher Partikelablösungseffekte zu prüfen und um die Laserbehandlung als Oberflächentechnologie für Teilchenbeschleunigervakuumsysteme zu validieren.:1. Motivation
2. Context of the study
3. Sample preparation and characterization methods
4. Fundamental dependencies of the surface properties on the laser parameters
5. Robot-assisted laser processing of curved surfaces
6. Large-scale treatments of beam screens
7. Conclusions and outlook
A. Appendix / The formation of electron clouds by secondary electron multiplication in the beam pipes of particle accelerators can lead to reduced performance during operation. Surface roughening using ultrashort pulse lasers efficiently reduces the secondary electron yield (SEY) of a surface. In this study, a solution for the suppression of electron clouds by laser structuring the inner copper walls of the Large Hadron Collider (LHC) beam tubes was developed, fulfilling the technical constraints and surface property requirements. For this purpose, fundamental dependencies between the laser processing parameters and the surface properties such as the modification depth, the surface chemical composition, the particle redeposition, and finally the SEY were investigated on a laboratory scale. A dedicated setup able to perform the modification treatment in situ, directly in the beam pipe hosted by the LHC magnet, was commissioned and the operation parameters were optimized. The device consists of a picosecond laser source, a beam coupling system, a 15 m long hollow-core fiber, and a robot that travels inside the beam tube. Treatment at low accumulated laser fluence in nitrogen flux resulted in ”optimal surface properties”, and specifically, a low modification depth (≈ 15 μm), low particle redeposition, a Cu2O-dominated surface and a SEY maximum of 1.4 after cleaning, which reduces to 1 upon electron irradiation at both room and cryogenic temperatures. A selective longitudinal scan scheme was developed to process the 10 m long beam pipes installed in the cryogenic magnet assemblies of the LHC with the highest effectiveness. A 3.1 m long laser-processed vacuum chamber was installed in
the LHC to validate the method with respect to particle detachment.:1. Motivation
2. Context of the study
3. Sample preparation and characterization methods
4. Fundamental dependencies of the surface properties on the laser parameters
5. Robot-assisted laser processing of curved surfaces
6. Large-scale treatments of beam screens
7. Conclusions and outlook
A. Appendix
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Anwendung ultrakurzer Lichtimpulse in der digital-holographischen Interferometrie / digital-holographische Hochgeschwindigkeitsinterferometrie mit ultrakurzer Belichtungszeit zur zeitaufgelösten Bewegungsanalyse im Einzelimpuls-Zwei-Wellenlängen-VerfahrenHansel, Thomas 06 September 2010 (has links)
In dieser Arbeit wird die digital-holographisch-interferometrische Zwei-Wellenlängen-Formerfassung sehr schnell bewegter Objekte behandelt und dafür unter Nutzung einer Ultrakurzpuls-Laserquelle mit der digitalen Einzelimpuls-Mehr-Wellenlängen-Holographie ein neuartigen Ansatz der digital-holographischen Aufnahme und Auswertung entwickelt. Mit der Entwicklung spezieller Methoden zur Formung der spektralen Signatur einer Ultrakurzpuls-Laserquelle hoher Leistungsdichte wurde zum ersten Mal die Voraussetzung für eine Zwei-Wellenlängen-Formerfassung hochdynamischer Objekte geschaffen. Die intrinsisch kurze Belichtungszeit unter einer Pikosekunde macht das Verfahren absolut stabil gegenüber Umwelteinflüssen. Für die simultane Aufnahme werden die spektral verschiedenen Hologramme mit einem eigens entwickelten Prinzip der Polarisationskodierung räumlich getrennt und zum ersten Mal mit zwei synchron laufenden Kameras gespeichert. Mit den in der digital-holographischen Einzelimpuls-Mehr-Wellenlängen-Interferometrie zusammengefassten numerischen Routinen zur Rekonstruktion und Phasenauswertung wird eine Zwei-Wellenlängen-Formerfassung mit mehreren Kameras möglich. In Anwendung des neuartigen Verfahrens an verschiedenen dynamischen Mikrosystemen konnte eine Genauigkeit von einem Zwanzigstel der erzeugten synthetischen Wellenlänge, bei der Auswertung der spektralen Differenzphase an Objekten in Reflexion erreicht werden. In einer digital-holographischen Hochgeschwindigkeitsformerfassung in Transmission wurden erstmals Bildfolgefrequenz von mehr als 0,4 kHz erreicht und der interferometrische Eindeutigkeitsbereich auf mehr als das 60-fache der optischen Wellenlänge ausgedehnt. Es wurden die Voraussetzungen für eine digitale Vier-Wellenlängen-Holographie geschaffen. Zukünftig wird eine Formerfassung mit einer Genauigkeit von 10nm über einen eindeutigen interferometrischen Bereich einiger 10 μm und die Untersuchungen von Prozessen auf einer Pikosekunden-Zeitskala möglich sein. / This work deals with the digital holographic interferometric two-wavelength contouring of very fast moving objects and develops with the digital single pulse multiwavelength holography a novel approach of digital holographic recording and analysis, using an ultrashort pulse laser source. The development of several methods to shape the spektral signature of an high power ultrashort pulse laser source provides the precondition for a two-wavelength contouring of highly dynamic objects for the first time. The intrinsically short exposure time shorter than a picosecond makes the system stable regarding external impacts. For the simultaneous recording the spektral different holograms are spatially separated in novel interferometric setups by the especially developed principle of polarization encoding and stored with two synchronized cameras for the first time. The digital holographic single pulse multi-wavelength interferometry combines the numeric routines of reconstruction and phase evaluation that make a two-wavelength contouring possible using more than one camera. The novel approach is successfully demonstrated on several dynamic microsystems. Evaluating the spectral phase difference for objects in reflection an accuracy of 2 μm, which corresponds to the twentieth of the realized synthetic wavelength, could be achieved. In a digital holographic high speed contouring in transmission a frame rate higher than 0,4 kHz was achieved for the first time and the interferometric range of unambiguity was extended larger than sixty times the optical wavelength. Furthermore, the developed digital holographic single pulse multi-wavelength interferometry is not limited to the evaluation of two wavelength. The principles of the method allow to perform digital four-wavelength holography. Future a contouring with an accuracy of 10nm over the unambiguous interferometric range of several 10 μm and the investigation of processes on a picosecond time scale will be possible.
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