Дисертації з теми "Impulsi laser"
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Empironi, Andrea. "Lavorazione laser ad impulsi di materiali metallici sottili alto-riflettenti: analisi di fattibilità." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Знайти повний текст джерелаTani, Silvio. "Applicabilità di sorgenti laser ad impulsi lunghi nella saldatura di ottone." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Знайти повний текст джерелаCarughi, Giovanni. "Lavorazioni laser ad impulsi di materiali metallici sottili alto riflettenti: analisi dei risultati." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Знайти повний текст джерелаMichau, Vincent. "Conversion de fréquence et compression d'impulsion d'un laser alexandrite par diffusion Raman stimulée intracavité." Paris 11, 1988. http://www.theses.fr/1988PA112065.
Повний текст джерелаSasoh, Akihiro, Koichi Mori, Kohei Anju, Koji Suzuki, Masaya Shimono, and Keisuke Sawada. "Diagnostics and Impulse Performance of Laser-Ablative Propulsion." American Institite of Physics, 2008. http://hdl.handle.net/2237/12005.
Повний текст джерелаSimoncig, Alberto. "The role of the electron recoiling mechanism in coherent light high-order harmonics generation: from the source to the applications." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3581.
Повний текст джерелаI processi di generazione di armoniche di ordine superiore (High-order Harmonic Generation o HHG) in gas inerti rappresentano, attualmente, la tecnica piu` promettente per la creazione di impulsi di luce coerente nell'estremo ultra-violetto (EUV) in una configurazione table-top. I processi HHG si basano sull'interazione non-lineare, tra impulsi laser ultra-corti, tipicamente dell'ordine della decina di femtosecondi, e atomi di gas inerti. Le caratteristiche che distinguono i processi HHG sono la loro durata temporale, che puo` essere nel dominio degli attosecondo e il fatto che l'interazione e` non perturbativa. Invece, la natura quantistica dei processi HHG implica la presenza di meccanismi di diffusione che influenzano la funzione d'onda dell'elettrone atomico coinvolto nell'interazione con il campo laser. Il ruolo della diffusione viene usualmente trascurato nella letteratura corrente, sebbene quest'ultima sia strettamente legata al controllo dell'efficienza del processo HHG e dello stato di polarizzazione dei fotoni generati. Il lavoro di tesi e` focalizzato sullo studio sperimentale e teorico/fenomenologico del ruolo dei meccanismi di diffusione, e sul loro controllo, al fine di incrementare l'efficienza e la qualita` ottica, i.e. coerenza, struttura temporale, etc., dei fotoni HHG prodotti. Gli studi e gli esperimenti condotti forniscono, in base alla nostra attuale conoscenza, la prima dimostrazione quantitativa a supporto del modello di Leweinstein. Accanto alla caratterizzazione spettrale, viene presentato uno studio accurato circa le condizioni minime necessarie a generare impulsi HHG, sempre legate al ruolo della diffusione della funzione d'onda elettronica. I risultati hanno permesso di ottenere una piu` profonda comprensione della complessa dinamica non-lineare, che sta alla base dei processi HHG. Accanto allo studio della diffusione si e` cercato di ottenere il controllo sullo stato di polarizzazione degli impulsi HHG, i quali mantengono la polarizzazione della radiazione laser utilizzata. La stessa diffusione impedisce di creare efficientemente armoniche di ordine superiore con polarizzazione ellittica (o circolare). Per risovere questo problema e` stata abbiamo sviluppato una collaborazione con il gruppo CXRO del Lawrence Berkeley National Laboratory, (Berkeley, USA), grazie al quale sono state realizzate una serie di ottiche multistrati innovative basate sul principio dell'angolo di Brewster, e disegnate appositamente per polarizzare circolarmente impulsi di luce EUV. Queste ultime sono state preliminarmente testate con successo sulla beam-line 6.3.2 del sincrotrone di Berkeley. La parte finale della tesi presenta la prima sorgente di impulsi HHG, polarizzati circolarmente utilizzando i citati multistrati. Per verificare l'efficienza e` di questi multistrati e` stato condotto un esperimento di dicroismo magnetico circolare con radiazioni EUV (EUV-MCD), unico nel sul genere, in quanto utilizza gli impulsi HHG polarizzati circolarmente per sondare il comportamento dicroico in corrispondenza delle soglie di assorbimento M di metalli ferromagnetici come Fe e Ni o delle loro leghe. Il fine ultimo e` dato dalla realizzazione di un esperimento risolto in tempo capace di utlizzare impulsi HHG circolarmente polarizzati per comprendere il processo di demagnetizzazione di sistemi ferromagnetici, sulla scala temporale del femtosecondo.
XXII Ciclo
1982
Delahaye, Hugo. "Lasers femtosecondes SWIR-MIR à fibres optiques pour la génération de rayonnements secondaires de l’EUV au MIR." Thesis, Limoges, 2020. http://www.theses.fr/2020LIMO0064.
Повний текст джерелаThe interaction between selfphase modulation and chromaticdispersion allows the installation of the solitonic regime, a solution of Schrödinger's equation in non-linear regime. In the case of subpicosecond impulses filling the condition of existence of the fundamental soliton, their largespectral bandwidth exposes them to 3rd order dispersion and Raman susceptibility. The interaction of these phenomena leads to soliton self-frequency shift. Solitonic fission and soliton self-frequency shift allow the generation of near 100 fs tunable wavelength pulses. The problem of the thesis can be summarized by the use of this phenomenon to develop high peak power sourcesat wavelengths, between 2 and 3 μm, not covered by MOPA and MOFA lasers. The design of fibres with a large modal area was necessary in order to achieve high peak power sources in the transparency band of silica. The study of the different fibres transparent in the mid-infrared was necessary as well as their integration in a MOFA sourcefor the conceptionof sources in the range [2,4;3] μm. The mastery of the solitonic regime properties allowedusthe generation of pulses of peak power close to and above MWin flexible fibres with a solid core (0.8MW to 1.7μm and 2.8MW to 2.2μm). Another result wasthe generation of soliton via a monolithic laser at wavelengths poorly covered>2.4 μm with peak powers (35kW to 2.75μm, 9kW to 3.01μm)
Miranda, Miguel Nicolau da Costa Ribeiro de. "Amplificação óptica de impulsos laser ultra-curtos." Master's thesis, Porto : edição do autor, 2006. http://hdl.handle.net/10216/64091.
Повний текст джерелаMiranda, Miguel Nicolau da Costa Ribeiro de. "Amplificação óptica de impulsos laser ultra-curtos." Dissertação, Porto : edição do autor, 2006. http://catalogo.up.pt/F?func=find-b&local_base=FCB01&find_code=SYS&request=000089810.
Повний текст джерелаAdamonis, Jonas. "High power Nd:YAG laser for pumping of OPCPA systems." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130925_093516-33211.
Повний текст джерелаDisertacija yra skirta sukurti, ištirti ir optimizuoti didelės galios Nd: YAG lazerių sistemą efektyviam moduliuotos fazės signalų optinių parametrinių stiprintuvų kaupinimui. Ypatingas dėmesys yra skiriamas Nd:YAG stiprintuvų išvadinių impulsų laikinių parametrų formavimui. Pademonstravome, kad Fabry-Pero interferometrų panaudojimas Nd:YAG dvipakopio regeneracinio stiprintuvo rezonatoriuose leidžia stiprinamų impulsų trukmę padidinti nuo ~ 60 fs iki 100 ps. Tuo tarpu išvadinių impulsų laikinės plėtros mastas bei gaubtinės moduliacijos gylis gali būti valdomas keičiant etalonų atspindžio koeficientą, o jų gaubtinės moduliacijos vertė mažiausia, kai etalonų storio santykis artimas 2. Sustiprintų impulsų kontrasto gerinimui pirmą kartą pritaikėme netiesinį antros eilės filtrą, veikiantį fundamentinės spinduliuotės poliarizacijos sukimo, išderintame antros harmonikos generatoriuje, efekto pagrindu. Tokiu būdu Nd:YAG stiprintuvuose sustiprintų impulsų kontrasto vertė pagerinta apie 102 kartų. Taip pat pademonstruota, kad Nd: YAG stiprinimo sistemos išėjime naudojant pakopinius antros harmonikos generacijos procesus, Gauso formos impulsus galima transformuoti į hipergauso impulsus. Sukurta didelės išvadinės energijos pikosekundinė Nd:YAG stiprintuvų sistema yra optiškai sinchronizuota su užduodančio femtosekundinio Yb:KGW osciliatoriaus impulsais ir turi ~ 300 mJ , 75 ps trukmės Gauso impulsų bei 100 mJ, > 100 ps trukmės hipergauso laikinės formos impulsų išvadus.
Meyers, Jason. "Tunable diode laser absorption spectroscopy characterization of impulse hypervelocity CO2 flows." Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210279.
Повний текст джерелаsensor could significantly aid in improving the knowledge of freestream static values thereby improving the models used in data rebuilding and numerical simulation. The design of such a sensor also expands the spectroscopic capabilities of the Von Karman Institute.
The absorption sensor is designed around the single P12 (00001)-(30013) rovibrational transition near 1.6µm (6218.09cm-1 specifically) which yields relatively weak direct absorption levels at about 3.5% per meter for typical Longshot freestream conditions. However, when handled carefully, adequate signal-to-noise can be acquired to exploit significant flow information. By being able to operate in this range, total sensor cost can be easily an a factor of two or more cheaper than sensors designed for the deeper infrared. All sensor elements were mounted to a compact portable optics bench utilizing single-mode optical fibers to allow for quick installation at different facilities by eliminating tedious optical realigning. Scans at 600Hz were performed over 20ms of the 40ms test time to extract core static temperature, pressure and velocity.
These results are compared with the current state of the Longshot data rebuild method. The non-uniform flow properties of the shear layer and test cabin rested gas accumulation was of an initial concern. The temperature and density gradients along with significant radial velocity components could result in DLAS temperature, pressure and velocity that are significantly different than that of the target freestream inviscid core values. Fortunately, with the proper selection of the P12 rotational number, this effect could be more or less ignored as the higher temperature and lower density gas of this region is relatively transparent.
Ultimately, acquired temperature and density were moderately accurate when compared to Longshot rebuilt results owing primarily to the baseline extraction which poses issues for such low absorption signals. However, the extracted velocity data are quite accurate. This is a definite puls for the sensor as the freestream enthalpy of cold hypersonic facilities is dictated primarily by the kinetic energy contribution. Being able to compare velocity gives insight to the level of vibration non-equilibrium in the flow. The velocity of the DLAS and the Longshot rebuild are quite close. This adds more weight to the argument that vibrational excitation is very low (if present at all) in the free stream and that the van de derWaals equation of state usage and constant specific heat assumption might be an adequate model for the data rebuild after all.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
Battocchio, Pietro. "Laser Ablation Propulsion: Synthesis and Analysis of Materials and Impulse Measurements." Doctoral thesis, Università degli studi di Trento, 2023. https://hdl.handle.net/11572/371607.
Повний текст джерелаDerrien, Thibault. "Nanostructuration de cellules photovoltaïques par impulsion laser ultracourte. : étude numérique des mécanismes de formation." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4005.
Повний текст джерелаUltrashort laser pulsed texturing is a process which allows to modify optical and electrical properties of matter, through formation of nano and micro structures on surface, appearing from pulse to pulse. Control of the process and developments of the potential applications need a good knowledge of the formation mechanisms. Processes occuring during the interaction are studied using numerical simulations and are compared to experimental results. The study aims to increase the efficiency of solar cells based on bulk silicon
Kuba, Jaroslav. "Etude expérimentale et théorique des lasers X pompés par une impulsion laser ultra-brève : pompage transitoire des ions d'argent nickeloi͏̈de." Paris 11, 2001. http://www.theses.fr/2001PA112295.
Повний текст джерелаThe objective of this thesis was to investigate both experimentally and theoretically a new type of X-ray lasers, the so-called transient collisional X-ray lasers. These lasers are pumped by a combination of a 'long' (5̃00 ps) and a 'short' (- 1 ps or less) driving laser pulses. This pumping scheme reduces dramatically the energy required to create the amplifying medium and hence allows to reduce the scale of the X-ray laser driver to a "table-top" class. Our work was mainly devoted to (1) the development and routine generation of a transient X-ray laser, emitting at 13. 9 nm (4d-4p transition in Ni-like Ag); (2) the detailed spatial and temporal characterisation of the emitted beam, and (3) a demonstration of its potential for applications. Three experimental campaigns were carried out at three different high-power laser facilities. In the first experiment, a partial improvement of the Ni-like silver X-ray laser beam characteristics, especially its horizontal divergence, was obtained by using a "two-colour" irradiation, in which the long pulse is frequency-doubled (2w). A new lasing line, emitted at 16 nm, was observed for the first time and attributed to a 4f-4d transition in Ni-like silver. When a travelling-wave irradiation was applied, a significant shortening of the X-ray laser pulse duration was demonstrated and explained by our model. In a subsequent experiment using a high-resolution streak camera, the duration of the 13. 9 nm transient X-ray laser was measured to be of 1. 9 ps. This is the shortest X-ray laser pulse ever demonstrated to-date. The results obtained were compared to analytical and quasi-analytical model calculations, as well as to a numerical simulation using a 1. 5D hydrocode. Finally in the third experiment, the X-ray laser beam was sent to a Fresnel bi-mirror interferometer and fringes with a good visibility were obtained. These preliminary results represent the first step towards interferometric applications with p̃s resolution
Labouret, Timothée. "Irradiation laser ultrabrève de nanobâtonnets d'or individuels en milieu aqueux : photo-génération de phénomènes d'intérêt biomédical." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC078/document.
Повний текст джерелаGold nanoparticles exhibit specific optical properties thanks to surface plasmon resonance. Laser irradiation close to their resonance frequency induces two main effects : a high absorption of the electromagnetic energy and an enhancement of the electromagnetic field in their close vicinity. In addition, gold is biocompatible. These three features have made them extremely useful for a number of light-triggered biomedical applications. In this field, gold nanorods (AuNRs) specifically show promise. Indeed, their resonance frequency can be tuned by changing their aspect ratio in order to match the window where biological media are relatively transparent (650–1350 nm). Their resonance then exhibits a high quality factor. As a result, light irradiation of AuNRs triggers various complex biological effects, especially when intense, ultrashort pulses are used. Nevertheless, the physics of irradiated AuNRs in aqueous media is only properly understood in more simple situations. That is why this thesis aims at reaching a better understanding of these multi-physics in biologically relevant irradiation conditions. It provides theoretical, numerical and experimental pieces of information about the transient optical response, the dynamics of energy transfer, the plasmon-assisted plasma generation, the photoluminescence and the production of reactive oxygen species. Each of these processes has biological or biomedical impact. Analyzing the underlying mechanisms reveals above all the major role of hot electrons in the ultrashort regime
Scurria, Giuseppe. "High power 2 μm fiber laser for mid-infrared supercontinuum generation in fluoride fibers". Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0342.
Повний текст джерелаHigh brightness and broad spectrum optical sources in the mid-infrared (mid-IR) are promising for different applications such as optronic countermeasures, LIDAR systems and spectroscopy. This thesis research work is dedicated to the investigation of high power supercontinuum generation in the 2-5 μm range. A thulium-doped fiber laser emitting at 2 μm has been built and characterized in continuous wave, Q-switching and Q-switched mode-locking regime. In continuous wave operation, as much as 45 W have been reached with a slope efficiency of 58%. The implementation of two fused-quartz end-caps fusion spliced at the extremities of the active-fiber improved the thermal management and the overall stability of the entire system in all mentioned regimes of operation, allowing for higher pump powers. In Q-switched mode-locking, the maximum average output power level was 40 W, for a Q-switch repetition rate of 150 kHz. At the average output power level of 20 W and 50 kHz of Q-switch repetition rate, the most energetic mode-locked pulse had an energy of 88 μJ and an estimated peak power of ~60 kW. In all the mentioned operation regimes, the measured beam parameter M2 of the fiber laser was 1.1, close to the diffraction limit. This laser has been used to pump fluoride optical fibers (ZBLAN and InF3) for supercontinuum generation in the 2-5 μm range. In ZBLAN, more than 10 W in all spectral bands have been obtained, with an output spectrum extending up to 4.4 μm. A conversion efficiency of 35%/28%/15%/8% has been measured for wavelengths longer than 2.15 μm/2.65 μm/3.1 μm/3.5 μm, respectively. For the InF3 fiber, a new design of an injection system, consisting of a large core diameter ZBLAN optical fiber and a commercial fiber-to-fiber coupler, allowed to enhance the thermo-mechanical stability of the fiber. The supercontinuum radiation generated in InF3 showed an output spectrum spanning up to around 4.7 μm with an output power level of 7 W in all spectral bands. To the best of our knowledge, this was the first Watt-level supercontinuum radiation in an InF3 fiber pumped by a singleoscillator
Salin, François. "Étude et réalisation d'une chaine laser femtoseconde : rôle des phénomènes solitons dans les lasers femtosecondes à dispersion contrôlée." Paris 11, 1987. http://www.theses.fr/1987PA112096.
Повний текст джерелаWe describe and analyze the production of femtosecond pulses in a passively mode-locked dye laser. We have studied theoretically the geometrical stability of the laser cavity and the influence of gain and loss saturation and group velocity dispersion on the pulse characteristics. These results are compare with the experimental observations obtained in a home-built femtosecond laser. We then present an experiment showing the soliton character of the pulses. In this experiment, we have observed high order solitons directly produced by a femtosecond laser. An amplifier with a 106 gain is described. We also pre sent a new system using four high index prisms to compensate the amplifier group velocity dispersion. We then show that femtosecond pulses can be analyzed using a single shot auto correlator. A last we present a new scheme to measure with a single pulse the temporal evolution of the optical Kerr effect in transparent materials
Weiss, Jiří. "Diagnostika impulzů Ti:Sa laseru pro generaci plazmatu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231778.
Повний текст джерелаRouzée, Arnaud. "ALIGNEMENT UNI ET TRIDIMENSIONNEL DE MOLÉCULES PAR IMPULSION LASER FEMTOSECONDE." Phd thesis, Université de Bourgogne, 2007. http://tel.archives-ouvertes.fr/tel-00398990.
Повний текст джерелаGame, G. W. "A laser guided gun launched projectile system using impulsive controls." Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760578.
Повний текст джерелаMENIS, THIERRY. "Reponse d'un systeme atomique simple a une impulsion laser femtoseconde." Paris 6, 1993. http://www.theses.fr/1993PA066176.
Повний текст джерелаSarafianos, Alexandre. "Injection de fautes par impulsion laser dans des circuits sécurisés." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2013. http://tel.archives-ouvertes.fr/tel-00944943.
Повний текст джерелаMauger, Sarah. "Couplage entre auto-focalisation et diffusion Brillouin stimulée pour une impulsion laser nanoseconde dans la silice." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00638962.
Повний текст джерелаGečys, Paulius. "Plonasluoksnių saulės elementų apdirbimas ultratrumpais lazerių impulsais." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121001_093544-75615.
Повний текст джерелаPresent 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.
Brikas, Marijus. "Silicio ir metalų mikroapdirbimas didelio impulsų pasikartojimo dažnio pikosekundiniais lazeriais." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110324_161301-79480.
Повний текст джерелаThe objective of the thesis is to investigate applicability of high pulse repetition rate picosecond lasers for microfabrication and to clarify high repetition rate pulse interaction with metals and silicon. The ablation threshold and accumulation rate dependence on the laser pulse duration for silicon and metals has been experimentally studied. The model of optimal focus conditions for the maximum ablation rate was developed and experimentally confirmed. The material evaporation rate decreases duo to plasma screening for high pulse energies. Various pulse length lasers have been used for cutting and drilling of silicon. In this work key properties of laser radiation, radiation absorption, ablation and plasma formation are discussed. Surface spectroscopy methods have shown that laser cutting of silicon in the air leads to the cut surface doping with carbon atoms up to 5 µm depth from carbon dioxide in the atmosphere, and the resulting silicon carbide influences the laser cut quality. Testing of applicability of high pulse repetition rate picosecond lasers for the production of complex shapes, relationships between surface roughness and process parameters were determined. Heat abstraction from the workpiece, during laser cutting of stents from nitinol, limits the potential use of the average laser power and the effective cutting speed The silver and gold picosecond laser ablation in the liquid medium generates a narrow size distribution of nanoparticles, which form a stable... [to full text]
Sasoh, Akihiro, In-Seuck Jeung, and Jeong-Yeol Choi. "Access to Space without Energy and Propellant on Board." American Institite of Physics, 2008. http://hdl.handle.net/2237/12050.
Повний текст джерелаCapdessus, Rémi. "Dynamique d'un plasma non collisionnel interagissant avec une impulsion laser ultra-intense." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR15268/document.
Повний текст джерелаRésumé en anglais
Pasquier, Corinne. "Ablation d'une cible solide diélectrique par une impulsion laser ultrabrève dans l'air." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0232/document.
Повний текст джерелаFew-cycle laser pulses offer remarkable capabilities for laser-matter interaction, especially for ablation of transparent dielectric materials. However, focusing ultrashort laser pulses in air implies natural limitations to linear beam propagation prior the target. In this context, we study the surface ablation of dielectrics with single 12 fs laser pulses in air, at intensities below and above the apparition of nonlinear effects in air. In particular, we establish the link between the fluence distribution at the laser focus, spanning from linear- to nonlinear- focusing regimes, and the ablated crater diameters. We demonstrate that the crater profile can be predicted despite significant beam reshaping taking place at high fluence, for fused silica and sapphire. Then, we identify an ablation regime where the beam is still unaffected by nonlinear effects in air. In these conditions, we developed an energy balance experiment, allowing characterizing the created plasma. We discuss and compare the results acquired on fused silica and sapphire. We show that in ablation regime the density plasma is below or nearby the critical density. Moreover, the beam penetration is higher in sapphire than in fused silica, yielding deeper craters
RENAUDIN, JEROME. "Etude par interferometrie de l'interaction d'une impulsion laser picoseconde avec un plasma." Paris 11, 1993. http://www.theses.fr/1993PA112202.
Повний текст джерелаFriou, Alexandre. "Propagation d’une impulsion laser intense dans un plasma sous-dense : creusement de canal et diffusion Raman stimulée." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112297/document.
Повний текст джерелаThis thesis is divided in two parts : i) the laser channeling in hundreds of microns long under-dense plasmas (0.1nc
Moreau, Julien. "Interaction d’une impulsion laser intense avec un plasma sous dense dans le régime relativiste." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0042/document.
Повний текст джерелаThe laser-accelerated ions draw an increasing interest due to their potential applications and to their unique properties. This manuscript presents a study of the interaction between a relativistic intense laser pulse and a low density plasma. In this regime, the plasma is transparent to the laser pulse and electrons oscillate with relativistic velocities in the field of the incident wave. These conditions make the transfer of the laser pulse energy to the plasma efficient, and therefore are interesting for the ion acceleration. This regime generates also electromagnetic and acoustic solitons whose formation mechanisms and properties need to be better understood. We carry out a detailed analysis of Particle-In-Cell simulations (performed with the code OCEAN) of interaction of an intense laser pulse with a low density plasma.We show that the stimulated Raman scattering (SRS) is the main mechanism responsible for the absorption of laser energy in plasma. This process is very efficient : it leads to the transfer of 70 % of the laser pulse energy to electrons. This instability occurs in plasmas with a density larger than the quarter critical one due to the decrease of the electron plasma frequency and develops in a very short time scale. It leads to an homogeneous electron heating all along the distance of propagation of the laser pulse through the plasma. The ions are efficiently accelerated at the plasma edges and can get nearly 30%of the initial laser energy. This study is accompanied by a simple analytical model which is able to predict and so optimize the laser backscattering fraction due to the development of the SRS instability. We also present a sequence of stages which lead to the formation of electromagnetic cavities. This analysis highlights the role of the modulationnal or Benjamin-Feir instability in the front of the laser pulse, which is split in a train of electromagnetic solitons. Our detailed study shows that these solitons excite plasmas waves in their wake, lose energy and are finally trapped in the plasma. They lead to the formation of density depressions (cavities) which may trap the electromagnetic fields produced in the plasma (by the SRS instability, for example). These structures may survive for a long time thanks to an equilibrium of the trapped field radiation pressure and the electronic kinetic pressure at their borders. These cavities absorb an significant part of the laser energy but only a part of it is trapped inside. The remaining part is invested in the cavity expansion, generation of acoustic solitons and acceleration of charged particles
Saugout, Sébastien. "Explosion coulombienne de H2 induite par une impulsion laser intense sub-10 fs." Phd thesis, Université Paris Sud - Paris XI, 2006. http://tel.archives-ouvertes.fr/tel-00154533.
Повний текст джерелаLa complémentarité des résultats expérimentaux et théoriques permet de mettre en évidence la translation des spectres d'énergie cinétique vers les énergies plus élevées lorsque la durée de l'impulsion diminue. Cette étude est réalisée pour des impulsions dans la gamme de 40 à 10fs expérimentalement et jusqu'à 1fs théoriquement. Cette étude montre également que, pour des durées d'impulsion laser inférieures à 4fs, la phase absolue devient un paramètre essentiel à prendre en compte. En outre, la dynamique moléculaire de H2 en champ laser intense ultracourt est également sensible à la valeur de l'éclairement crête de l'impulsion. Les résultats théoriques et expérimentaux montrent que les spectres d'énergie sont centrés autour d'une énergie plus élevée quand l'éclairement augmente. Par ailleurs, deux régimes d'ionisation double sont également mis en évidence théoriquement pour des impulsions de 4fs. La sensibilité de H2 à la qualité temporelle de l'impulsion laser permet une détection, par l'intermédiaire des spectres expérimentaux d'énergie cinétique, des pré- ou post-impulsions susceptibles d'apparaître autour de l'impulsion laser principale. Enfin, les différents types d'ionisation double sont étudiés et les résultats mettent en évidence la dynamique électronique attoseconde de la recollision et l'influence de cette dernière sur la dynamique nucléaire femtoseconde.
Ribière, Maxime. "Spectroscopies d'émission et d'absorption appliquées à l'analyse de plasmas produits par impulsion laser." Phd thesis, Université de Rouen, 2008. http://tel.archives-ouvertes.fr/tel-00443037.
Повний текст джерелаBeuton, Romain. "Modélisation de la structuration d'un matériau diélectrique irradié par une impulsion laser femtoseconde." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0231/document.
Повний текст джерелаFemtosecond laser pulses are an efficient tool to induce localized structural modifications in the bulk of dielectrics materials. The dielectrics, initially transparent, start to efficiently absorb the energy when the laser intensity exceeds the optical breakdown threshold of the material. This property, coupled to a femtosecond pulse duration smaller than the caracteristic relaxation times of matter, allows to induce a localized and accurate energy deposition in the irradiated volume. In order to model the formation of such structures, a 2D thermo-elasto-plastic model, including solid-liquid transitions through a softening model, has been implemented in a lagrangian hydrodynamic code. Studies on the formation of a single cavity and several interacting cavities have been firstly performed, assuming an instantaneous energy deposition in the bulk of fused silica. The relaxation of the heated matter, transformed to a warm dense plasma, induces shock waves in the surrounding cold solid. Permanent deformations may appear if the stress, induced by the waves, exceeds the yield strength of the material. This first study allowed to understand and describe the various steps of the micro-structures formation, which are strongly correlated to the elasto-plastic behavior of the surrounding solid. Furthermore, by using a Weibull’s law, accounting for defects density in the material, cracks probabilities have been predicted. Secondly, the structuration of fused silica by a Bessel beam has been considered. For that purpose, a 3D Maxwell solver coupled to a fluid description of the electron dynamics has been used to model the laser energy deposition. Results allow to understand how the energy deposition establishes and show the effects of the different ionization processes on the electron density and energy profiles. Then, thermo-elasto-plastic simulations have been carried out including the calculated energy deposition. Various kinds of induced deformations in fused silica have been obtained depending on the incident pulse energy and duration, which is in agreement with experimental observations
Camenen, Loïc. "Modélisation et analyse de la réponse du couvert végétal à une impulsion laser." Aix-Marseille 1, 1994. http://www.theses.fr/1994AIX11050.
Повний текст джерелаWoo, Tak Kwong. "Transitory control of separated shear layer using impulsive jet actuation." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52980.
Повний текст джерелаBastiani-Ceccotti, Séréna. "Etude et optimisation de l'émission x d'un plasma créé par une impulsion laser ultra-courte." Palaiseau, Ecole polytechnique, 1998. http://www.theses.fr/1998EPXX0011.
Повний текст джерелаDouti, Dam-Bé Lardja. "Tenue au flux et physique de l'interaction laser/matière dans les couches minces optiques en régime sub-picoseconde." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4347/document.
Повний текст джерелаLaser fluence resistance of optical surfaces is a major challenge for the development of high power and short duration pulse lasers. Studies on laser matter interactions show that the damage initiation is the result of highly nonlinear excitation process such as photoionization, impact ionization and electronic avalanche. In this PhD thesis we focused on the study of the damage and the response of materials after this initiation and their dependence with laser parameters, this in order to better understand the complex mechanisms of damage, identify laws of relevant scales for applications, and enable new optical design with higher laser resistance and lifetimes. A multi parametric experimental testing setup was developed for studying laser resistance of optical components. To collect new data on thin film materials damage dependences, which have been less studied in the literature, different experimental studies have been conducted on dielectrics, in coating or bulk form. The study of the dependency of damage with laser wavelength reveals different ranges characterized by the electronic processes occurring during the interaction. We have considered also the effect of multiple pulse irradiations, with different wavelengths and on coatings realized by different technologies. All these experimental results have been discussed with the help of a numerical simulation model we have developed and presented in this thesis. We have also proposed an original method based on optical phase difference measurement for damage characterization and study. We finished with some experiments on the time resolved microscopy measurements and investigations of damage processes
Kumar, Nishant. "MAC and Physical Layer Design for Ultra-Wideband Communications." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/9934.
Повний текст джерелаMaster of Science
FALLIES, FLORENCE. "Etude numerique et experimentale de l'interaction d'une impulsion laser subpicoseconde avec une cible solide." Paris 6, 1994. http://www.theses.fr/1994PA066363.
Повний текст джерелаQuaglia, Luca. "Etats électroniques des ions moléculaires multichargés transitoires produits par une impulsion laser femtoseconde intense." Paris 11, 2001. http://www.theses.fr/2001PA112336.
Повний текст джерелаElectronic states of transient multicharged molecular ions produced by an intense femtosecond laser pulse are studied using different experimental and theoretical techniques. Highly excited states are investigated in the 101̂7 W/cm2̂ laser intensity range with the help of fluorescence spectra of multicharged atomic fragments coming from the molecular explosion. These measures show the existence of highly excited multicharged molecular ions in a straightforward way. The production, efficiency of these highly excited ions strongly depends on the initial electronic configuration. Low excited states studies are based on fragmentation kinetic energy release spectra in the 101̂5-101̂6 W/cm2̂ laser intensity range. These spectra are analyzed with the help of calculations of potential energy curves of multicharged molecular ion electronic states. For the fragmentation of N2 and O2 molecules, the comparison of experimental and theoretical results shows the existence of several low excited states of the corresponding molecular ions and allows to explain the fragmentation energy release of (N2) ̂4+ and (O2)4̂+ ions without resorting to any stretching of the molecule during the multiple ionization process. Population of highly excited states is studied using a two-pulse experimental set-up based on the fragments emission anisotropy. The origin of this anisotropy is experimentally investigated and interpreted with the help of a Thomas-Fermi bidimensional model of the laser-molecule interaction. Pump-probe experiments show that the population of highly excited states is negligible in the 5x101̂5 W/cm2̂ laser intensity range. The fragments emission anisotropy is due to a very fast re-orientation of the molecular system. Theoretical calculations show that re-orientation takes place during the multiple ionization process and Coulomb explosion and gets faster as the laser intensity is increased
Wolfersberger, Delphine Kugel Godefroy. "ETUDE EXPERIMENTALE ET THEORIQUE DE L'AUTO-FOCALISATION PHOTOREFRACTIVE D'UNE IMPULSION LASER POUR APPLICATION A LA LIMITATION OPTIQUE /." [S.l.] : [s.n.], 1999. ftp://ftp.scd.univ-metz.fr/pub/Theses/1999/Wolfersberger.Delphine.SMZ9922.pdf.
Повний текст джерелаGrishin, Mikhail. "Dynamics of continuously pumped regenerative laser amplifiers." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110628_134556-72562.
Повний текст джерелаŠioje disertacijoje tiriami nuolatinai kaupinami regeneraciniai stiprintuvai su ilgos relaksacijos trukmės lazerine terpe. Tikslas buvo išanalizuoti bendrus tokių sistemų sudėtingos dinamikos dėsningumus pasireiškiančios aukštų dažnių diapazone ir surasti būdą pasiekti maksimalias išėjimo impulsų energijas išlaikant jų stabilumą. Analitiškai aprašomos pagrindinės optimizuotų ir stabiliame režime veikiančių stiprintuvų charakteristikos, tokios kaip optimalūs pradinis ir galutinis stiprinimo koeficientai, maksimali išėjimo impulso energija, rezonatoriuje išsklaidytoji galia, daugelio praėjimų B-integralas ir rezonatoriaus apėjimų skaičius, su kuriuo gaunama maksimali išėjimo impulso energija. Nustatytos egzistuojančių dinaminių režimų (stabilaus, kvaziperiodinio ir chaotinio) sritys valdančiųjų parametrų erdvėje. Išsiaiškinta, kad nestabilaus veikimo sritis mažėja, kai užkrato impulso energija didėja. Sukurtas ir išplėtotas stabilumo diagramų metodas, kuris ne tik suformuoja sisteminį požiūrį į regeneracinio stiprinimo dinamikos optimizavimą, bet ir leidžia nustatyti užkrato energijos dydį, pakankamą stabiliam veikimui palaikyti. Nustatytos darbinės charakteristikos kritiniame impulsų pasikartojimo dažnių diapazone, kur neegzistuoja analitiniai sprendiniai ir nestabilumai yra labiausiai tikėtini. Teoriniai rezultatai patvirtinti eksperimentiškai diodais kaupinamoje pikosekundinėje Nd:YVO4 lazerinėje sistemoje. Pademonstruota, kad užkrato impulso energijos padidinimas susiaurina... [toliau žr. visą tekstą]
Degorce, Jean-Yves. "Dynamique hors équilibre de phénomènes de transport dans un solide absorbant, soumis à une impulsion laser." Bordeaux 1, 2005. http://www.theses.fr/2005BOR12950.
Повний текст джерелаChorel, Marine. "Étude des traitements multicouches utilisés dans un environnement à faible hygrométrie sur les installations laser de puissance." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0188/document.
Повний текст джерелаThe chirped pulse amplification demonstrated in 1985 allowed the development of petawatt class laser such as Petal (Petawatt Aquitaine Laser). The increase of power of those facilities is limited by the resistance to laser-induced damage of the optical components placed after the compression stage. The aim of this thesis is to improve the laser-induced damage threshold of those components which are multilayer dielectric mirrors. Three paths of improvement are considered the change of design (number of layer, thicknesses), of materials and/or deposition process. A numerical study allows evaluating the potential improvement brought by two of those paths. This led to the development of a design optimization algorithm that required the prior characterization materials. Consequently, various materials deposited as single layers were laser damage tested and optically characterized to evaluate the adequacy of the materials with the deposition process. The results show a wide discrepancy that cannot be explained by the laws exposed in the literature. However, a good correlation was found between the intrinsic laser-induced damage thresholds in the infrared with the absorption in the ultraviolet confirming the influence of the multiphoton absorption in the laser-induced damage mechanisms. Finally, those experimental results combined with the optimization algorithm allowed the development of mirror samples that exhibit laser-induced damage threshold 73% higher than one of classical mirrors
Micheau, Samuel. "Etude théorique de l'interaction entre une impulsion laser intense et un agrégat de gaz rare." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2007. http://tel.archives-ouvertes.fr/tel-00186659.
Повний текст джерела- Nous avons introduit des processus d'ionisation d'ordres supérieurs en incluant des états excités intermédiaires X^{q+} + e- -> X^{q+*} +e- -> ... -> X^{(q+1)+} +2 e-. Nous avons pour cela utilisé une approche potentiel modèle pour décrire la structure électronique des ions (ou atomes) de l'agrégat et nous avons évalué les sections efficaces totales d'excitation et d'ionisation collisionnelles suivant le formalisme des ondes distordues.
- Nous avons étudié l'influence des phénomènes d'écran induits par la densité d'électrons libres sur la dynamique de l'interaction. A l'aide d'un potentiel d'écran sophistiqué, nous avons montré que les effets d'écran augmentent les sections totales d'ionisation et réduisent les sections d'excitation par rapport aux données non écrantées.
Le modèle nanoplasma amélioré permet à présent de reproduire les populations d'états de charge très élevés observées expérimentalement ainsi que la variation de l'émission He_alpha provenant d'agrégats d'argon en fonction des différents paramètres de l'interaction (durée d'impulsion, taille d'agrégat, éclairement crête, longueur d'onde). Nous avons également simulé les spectres d'émission X résolus en temps et en énergie. Ces spectres indiquent une durée d'émission ultra-brève (inférieure à 100 fs), et confirment ainsi que l'interaction laser-agrégat est une source de rayonnement utilisable dans le cadre d'applications à la science X ultra-rapide.
Lefebvre, Erik. "Mecanismes d'absorption et d'emission dans l'interaction d'une impulsion laser ultra-intense avec une cible surcritique." Paris 11, 1996. http://www.theses.fr/1996PA112320.
Повний текст джерелаEngin, Selma. "Étude théorique du contrôle de la dissociation moléculaire par impulsion laser et spectroscopie de photoélectrons." Paris 6, 2013. http://www.theses.fr/2013PA066524.
Повний текст джерелаThis thesis presents a new type of pump-probe scheme which consists to follow by photoelectron spectroscopy (probe) the stretching dynamics of the chemical bond of hydrogen chlorine excited by infrared laser pulse (IR pump). The originality of this new device comes from the use of the Raman Chirped Adiabatic Passage (RCAP) technique for the IR pump and the core electron spectroscopy (XPS or ESCA) for the X probe. The RCAP process allows the system to climb the vibrationnal ladder selectively and sequentially and then probed by x-ray thanks to its chemical environment sensitivity. In this manuscript, the theoretical developments, the numerical tools which are essential to simulate the pump-probe RCAP-X device and the electronic structure of HCI are presented. The interaction between the molecule and the IR-pulse is simulated in realistic conditions, taking into account the orientation effects of the molecule and the rotational dynamics (temperature). The best population transfer conditions are defined by the research of the best laser parameters (intensity, chirp). The calculated photoelectron spectrum shows a shift as a function of the pulse duration of the satellite bands which are assigned to shake-up process. This evolution is the signature of a vibrational dynamics. The theoretical study developed in this manuscript show that this pump-probe device could be efficient with the use of Titan-Sapphire lasers which has intensity around 5x1012 W/cm2 and which could be chirped with a chirp around 10-5,10-6 eV/fs in conditions of low temperature (<80°K)
Juhel, Marc. "Traitement de surface par une impulsion laser de 15 nanosecondes : application à la formation d'alliages." Grenoble 1, 1990. http://www.theses.fr/1990GRE10111.
Повний текст джерелаFabretti, Valérie. "Modélisation de l'émission X des raies K. Alpha dans les plasmas créés par impulsion laser ultracourte (sub-picoseconde) et ultra-intense (10 puissance 18W cm-2)." Aix-Marseille 1, 1997. http://www.theses.fr/1997AIX11075.
Повний текст джерела