Abstract In this dissertation a rigorous analysis is performed on the reentrant non-planar ring laser cavity constructed by the Herriott-type multi-pass cell. Since the non-planar ring cavity is a non-orthogonal cavity, so the ABCD matrix method used to analyze the beam propagation is not valid. A rigorous method using Gaussian beam propagation is needed. The beam rotation, astigmatism, and spherical aberration are considered to obtain a self-consistent solution of the Gaussian beam. It turns out that spherical aberration is a very important issue for this non-planar resonator. Without taking into account the spherical aberration, a stable resonator would be difficult to realize. By using a self-consistent Gaussian beam propagation method, the characteristic of laser beam was analyzed and compared with that of the ABCD approximation method. The reentrant ring cavity is very sensitive to cavity length, especially when the planar and non-planar configurations have the same output beams; therefore, it is very important to consider a rigorous method using Gaussian beam propagation. By considering the coordinate transformation of the beam after mirror reflection, a non-planar figure-8 ring cavity can be treated as an orthogonal cavity except for an exchange of tangential and Sagittal planes after each reflection. A simple astigmatic Gaussian beam approach is used to analyze the non-planar figure-8 ring cavity, and an analytic solution is obtained. For the general case of the multi-pass non-planar ring cavity, a general astigmatic Gaussian beam approach is used to treat the problem. The general form of mirror phase shift is used, and two important differences compared to the ABCD method were found. Firstly, the spot size is always elliptical while the spot size is circular using the ABCD approximation. Secondly, a second stable region is found in the cavity, the width of the second stable region is smaller than the first stable regi

Diode laser pumped solid state laser is compact, and can generate high peak power laser with good output mode. It has been applied extensively in electronics, communication, and medical treatment in recent years. The purpose of this study is to develop a compact and practical ring laser system. The multi-reentrant ring laser system developed in this work composes of two spherical mirrors and a gain medium where the conventional ring laser systems have at least three mirrors to construct the laser cavity. The laser system is more compact and simple than conventional ring laser systems. It can be used for producing single frequency green and blue lasers. The laser system can also be applied in aviation, trace detection as well as compact picosecond mode-locked laser. We not only prove that the multi-reentrant laser system is feasible theoretically and experimentally, but also use the fundamental laser theory to find the relation among cavity length, number of points, number of circulation, and the distance between center of gain medium and optical axis. The exact solution we obtained is experimentally verified with good agreement. A comparison between exact solution and paraxial approximation is also performed. The beam paths observing from the top, side, and end view are analyzed for various multi-reentrant laser cavities. The stability of the cavity is numerically analyzed and experimentally verified with good agreement, too. Finally, the differences in cavity configuration between TEM01 mode and the figure-8 mode are compared in this thesis.

In the past three decades, Nd:YAG has been the dominating high power solid-state laser gain medium. Compared with Nd:YAG, Yb:YAG has lower quantum defects which produces less heat so that it can reduce thermo-optical deformation. In addition, the achieved doping concentration can be 100%, and the absorption FWHM at 941 nm is 18 nm. Based on above listed advantages, Yb:YAG has the potential to replace Nd:YAG. Using Yb:YAG as the laser gain medium in reentrant two-mirror laser cavity, we have succeeded in Yb:YAG ring laser and all the intracavity elements are coated by our electron gun deposition system. The main purpose of my research is to continue the previous result (slope efficiency: 20.1%), and further increasing the slope efficiency of our ring cavity with different round-trip transmittance of couplers. Besides, we measured and analyzed the polarization of the planar and non-planar ring cavities. At present, the highest slope efficiency we achieved is 38.9% with a round-trip transmittance of 16.4%.

Les fibres optiques en silice dopées ytterbium sont couramment utilisées pour des applications laser à forte puissance depuis plusieurs années. Ces puissances ne cessent de croître en raison de progrès continus sur les procédés de fabrication des fibres optiques. Cette thèse s’intéresse à l’élaboration de cœurs de fibres optiques en silice vitreuse dopée ytterbium par un procédé plasma (SPCVD). Cette technique a été inventée en 1986 pour la fabrication de fibres optiques de télécommunications et nous l’avons adaptée dans ces travaux de thèse à la fabrication de cœurs de fibres à grande aire effective dopés en terres rares. Dans un premier temps, la mise au point du procédé et des différentes sources d’évaporation des précurseurs est présentée. Les principaux cœurs de fibres élaborés sont très riches en silice, et faiblement dopés en aluminium, en fluor et en ytterbium. L’homogénéité radiale et longitudinale des cœurs est discutée, et plusieurs options sont proposées pour l’améliorer. Dans un deuxième temps, la structure du réseau vitreux des cœurs élaborés ainsi que l’environnement et la dispersion de l’ion Yb3+ au sein du réseau vitreux silicaté sont étudiés. Pour cela, une approche multi-spectroscopique est utilisée : la résonance magnétique nucléaire informe sur l’environnement des noyaux à spin nucléaire non nul 29Si, 27Al et 19F tandis que la résonance paramagnétique électronique à impulsions permet à la fois de sonder spécifiquement l’environnement de l’ion Yb3+ et d’étudier sa dispersion au sein du réseau vitreux. Ces expériences sont complétées par des caractérisations optiques telles que l’absorption et la luminescence des ions Yb3+. Enfin, les cœurs de fibres élaborés par la méthode SPCVD sont caractérisés en cavité laser. L’efficacité de conversion, la qualité de faisceau et la résistance au photonoircissement de plusieurs cœurs aluminosilicatés co-dopés en fluor et en ytterbium sont présentés. / Ytterbium-doped silica optical fibers are widely used for high power laser applications for several years. These powers keep on increasing due to continuous improvements in optical fibers fabrication processes. The aim of this PhD is to synthesize ytterbium-doped silica optical fibers’ cores using a plasma process named SPCVD. This method has been created in 1986 for telecommunications optical fibers synthesis, and we have adapted it to fit the fabrication of rare earth-doped large-mode-area optical fiber cores. We first present the development of ways of evaporating low vapor pressure reagents. All the synthesized optical fiber cores are silica-rich, and slightly doped with both aluminum, fluorine and ytterbium. Radial and longitudinal homogeneities are discussed, and we propose several options in order to improve them. Then, the glassy network structure of the fabricated cores and also the neighborhood and dispersal of Yb3+ ion in the silicate network are studied. Thus, we used several spectroscopic studies: nuclear magnetic resonance enables to focus on non-zero nuclear spin nucleus (29Si, 27Al, 19F) whereas electronic paramagnetic resonance is used to probe the neighborhood and the dispersal of Yb3+ ions. We also based our study on optical characterizations as absorption and luminescence of Yb3+ ions. Finally, the fibers’ cores we synthesized using the SPCVD process have been characterized in a laser cavity. We present the power conversion efficiency, the beam quality and the resistance to photodarkening of several ytterbium and fluorine-co-doped aluminosilicate cores.

RésuméLa diffraction et la diffusion de rayons X sont utilisées dans de nombreux domaines de la physique, de la médecine et de la technologie. Des faisceaux de haute brillance sont néanmoins requis pour améliorer les performances de ces techniques. L’utilisation de la diffusion Compton d’un laser sur un faisceau d’électrons présente un grand intérêt pour la production de rayons X. Ce processus permet l’emploi d’un anneau de stockage d’électrons compacts et d’un résonateur optique pour accroître la puissance laser. Avec un tel système, un taux de collision laser-électron supérieur au méga Hertz est envisageable permettant d’atteindre un flux de rayons X de l’ordre de 10¹³ photons/s. Dans le premier chapitre, je décris les motivations pour le développement d’une source de rayons X basée sur la diffusion Compton et utilisant un résonateur optique. Je détermine aussi les performances que l’on peut attendre de ce type de sources ainsi que l’état de l’art actuel dans ce domaine. Dans le deuxième chapitre, je décris le comportement et les propriétés des résonateurs optiques en régime impulsionnel. J’introduis la notion de phase CEP (‘carrier envelope phase’) et je montre la nécessité de contrôler à la fois la fréquence de répétition de l’oscillateur laser et cette phase CEP. Le chapitre 3 est consacré aux oscillateurs fibrés à blocage de mode. Je montre les performances du laser que j’ai construit en utilisant le phénomène de rotation de polarisation non-linéaire.La méthode d’asservissement laser-résonateur optique ‘tilt locking’ est introduite au chapitre 4. Je décris tout d’abord les études de simulations et le montage expérimental qui ont permis de tester la méthode en régime impulsionnel. Je donne ensuite les résultats expérimentaux qui démontrent la faisabilité de la méthode ‘tilt locking’ en régime impulsionnel. J’effectue aussi une comparaison expérimentale des performances de la méthode ‘tilt locking’ avec la méthode classique ‘Pound-Drever-Hall’. Je termine le chapitre en indiquant une difficulté expérimentale de la méthode pour générer plusieurs signaux d’erreurs.Je décris la conception du système optique de la machine Compton TTX de l’université Tsinghua dans le chapitre 5. Les performances attendues pour cette machine sont des flux de rayons X compris entre 10¹º et 10¹³ photons/s. / X-ray diffraction and scattering, X-ray spectroscopy, and X-ray crystallography are widely used in the life sciences, material science, and medical diagnosis. High-quality and high-brightness X-rays are a strong requirement to improve applications. Inverse Compton scattering (ICS) X-ray source has attracted great interests worldwide lately. To significantly enhance the average X-ray photon flux, a compact electron storage-ring combined with a high finesse optical enhancement cavity (OEC) can be utilized. In such a system, the collision rate between the electron beam and the laser pulse is greatly increased to the MHz range, enabling a photon flux up to 10¹³ph/s.In the first chapter, I describe the motivation behind the development of OEC based on ICS X-ray source. The characteristics of this kind of X-ray source are summarized, compared to those of the conventional low-repetition-rate Terawatt laser system based on ICS X-ray source. The latest progress and research status of OEC based on ICS X-ray source are presented. Pulsed-laser injected high-finesse OEC stacking theory and properties are discussed in Chapter 2. Not only does the OEC based on ICS X-ray source require the laser pulse repetition rate to be matched to the free spectral range (FSR) of the cavity, where both also have to match the electron storage-ring circulation frequency. In addition, we have to match the phase shift of the laser repetition rate to the phase offset introduced by the dispersion of the cavity mirrors, since our cavity finesse design value is quite high. The stacking theory is analyzed in the frequency domain. Cavity properties, including cavity mirror dispersion, finesse, and FSR, are discussed in detail. A laser frequency comb and OEC coupling is analyzed also. The laser source development is presented in Chapter 3. We constructed a mode-locked fiber laser based on nonlinear polarization rotation. The locking model, locking techniques, and the theory, simulations and experimental tests of tilt locking (TL) in the pulsed laser injected high-finesse OEC are discussed in Chapter 4. We succeeded in locking a pulsed laser to a high-finesse cavity with the TL technique. The experimental results show that the TL and the Pound–Drever–Hall techniques have the same performance: stable locking, high sensitivity, and the same power coupling rate for picosecond laser pulse case, while the test results for full spectrum TL locking show that it is uneasy to align the split-photodiode to the beam waist.Based on the above experimental study and tests, we design the OEC system for Tsinghua University X-ray project in Chapter 5. The expected X-ray flux is 10¹º to 10¹³ ph/s. We detail every subsystem requirement.

Les travaux de cette thèse s'efforcent d'apporter une solution au problème persistant de grande pauvreté des lasers à fibre à modes bloqués, en termes de fonctionnalités et de flexibilité. La thèse propose une cavité laser fibrée ayant comme spécificité d'être multifonctionnelle. La cavité est dotée de composants accordables, qui apportent la flexibilité nécessaire pour réaliser des fonctions allant de la génération d’impulsions aux profils complexes (solitons, bi-solitons, tri-solitons, etc) jusqu’à la sculpture des profils d’impulsion, en passant par la régulation des puissances crête, et la régénération de profils d’intensités sévèrement dégradés. La cavité laser que nous proposons a comme spécificité d'être pilotée par un composant clé, qui est un miroir à boucle optique non-linéaire (NOLM : Nonlinear Optical Loop Mirror) multifonction. Nous avons conçu ce NOLM en apportant des modifications structurelles dans l'architecture usuelle de ce dispositif, et en lui adjoignant : une fibre compensatrice de dispersion, un filtre passe bande à bande passante accordable, et un amplificateur (précédé d'un filtre égaliseur de gain, selon le besoin). Le NOLM ainsi conçu est doté de deux paramètres manuellement accordables, à savoir: la bande passante du filtre passe bande et la puissance de pompage de l'amplificateur. Ces deux paramètres permettent de régler sa fonction de transfert, et à accroître ainsi ses fonctionnalités et sa flexibilité. Ainsi, en plus de son rôle comme élément déclencheur du blocage de modes, ce NOLM réalise des fonctions optiques essentielles telles que la régénération des profils d'intensité fortement dégradés par des phénomènes de propagation ; ce qui contribue au renforcement de la stabilité du laser. Nous démontrons également la possibilité de réguler la puissance crête des impulsions, en la verrouillant à une valeur prédéfinie. Nous montrons enfin que le laser multifonction offre la possibilité de réaliser la sculpture des profils d'impulsion, c'est-à-dire, de générer des impulsions dotées d'une puissance crête et une largeur temporelle fixés à l'avance via un réglage approprié des paramètres de contrôle du NOLM.Les applications visées par ce laser multifonction, concernent toutes les activités qui requièrent des sources d'impulsions finement accordables, tant au niveau de puissance crête des impulsions que de leur largeur temporelle. Ces activités, nombreuses dans le domaine Télécom, incluent les opérations de remise en forme des porteuses d'information, les opérations de compression ou étirement de profil d'impulsion, les diagnostics de composants optiques et contrôles non destructifs des lignes de transmission par réflectométrie. / The work of this thesis strives to provide a solution to the persistent problem of poverty of mode-locked fiber lasers, in terms of functionality and flexibility. The thesis proposes a fiber-laser cavity having the specificity of being multifunctional. The cavity is equipped with tunable components, which provide the flexibility to realize functions ranging from the generation of pulses with complex profiles (solitons, bi-solitons, tri-solitons, etc.) up to the carving of pulse profiles, passing through the regulation of peak powers, and the regeneration of severely degraded intensity profiles. The laser cavity that we propose has the specificity of being controlled by a key component, which is a multifunctional nonlinear optical loop mirror (NOLM). We have designed this NOLM by making structural modifications in the usual architecture of this device, and by adding to it: a dispersion compensating fiber, a bandpass filter with tunable bandwidth, and an amplifier (preceded by a gain flattening filter, as needed) with tunable gain. These two parameters make it possible to adjust its transfer function, and thus to increase its functionalities and its flexibility. Thus, in addition to its role as a trigger for mode locking, this NOLM performs essential optical functions such as the regeneration of strongly degraded intensity profiles; which contributes to strengthening the stability of the laser.We also show the possibility of regulating the pulse peak power by locking it around a predefined value. Finally, we show that the multifunction laser offers the possibility to carve pulse profiles, that is, to generate pulses endowed with a peak power and a temporal width set in advance through an appropriate adjustment of the NOLM control parameters. The applications targeted by this multifunction laser are those requiring pulses with finely tunable peak power and temporal width. These activities, include the pulse reshaping in Telecoms, operations of compression or stretching of pulse profiles, optical component diagnostics, and non-destructive control of transmission lines

X-ray diffraction and scattering, X-ray spectroscopy, and X-ray crystallography are widely used in the life sciences, material science, and medical diagnosis. High-quality and high-brightness X-rays are a strong requirement to improve applications. Inverse Compton scattering (ICS) X-ray source has attracted great interests worldwide lately. To significantly enhance the average X-ray photon flux, a compact electron storage-ring combined with a high finesse optical enhancement cavity (OEC) can be utilized. In such a system, the collision rate between the electron beam and the laser pulse is greatly increased to the MHz range, enabling a photon flux up to 10¹³ph/s.In the first chapter, I describe the motivation behind the development of OEC based on ICS X-ray source. The characteristics of this kind of X-ray source are summarized, compared to those of the conventional low-repetition-rate Terawatt laser system based on ICS X-ray source. The latest progress and research status of OEC based on ICS X-ray source are presented. Pulsed-laser injected high-finesse OEC stacking theory and properties are discussed in Chapter 2. Not only does the OEC based on ICS X-ray source require the laser pulse repetition rate to be matched to the free spectral range (FSR) of the cavity, where both also have to match the electron storage-ring circulation frequency. In addition, we have to match the phase shift of the laser repetition rate to the phase offset introduced by the dispersion of the cavity mirrors, since our cavity finesse design value is quite high. The stacking theory is analyzed in the frequency domain. Cavity properties, including cavity mirror dispersion, finesse, and FSR, are discussed in detail. A laser frequency comb and OEC coupling is analyzed also. The laser source development is presented in Chapter 3. We constructed a mode-locked fiber laser based on nonlinear polarization rotation. The locking model, locking techniques, and the theory, simulations and experimental tests of tilt locking (TL) in the pulsed laser injected high-finesse OEC are discussed in Chapter 4. We succeeded in locking a pulsed laser to a high-finesse cavity with the TL technique. The experimental results show that the TL and the Pound-Drever-Hall techniques have the same performance: stable locking, high sensitivity, and the same power coupling rate for picosecond laser pulse case, while the test results for full spectrum TL locking show that it is uneasy to align the split-photodiode to the beam waist.Based on the above experimental study and tests, we design the OEC system for Tsinghua University X-ray project in Chapter 5. The expected X-ray flux is 10¹º to 10¹³ ph/s. We detail every subsystem requirement.

X-ray diffraction and scattering, X-ray spectroscopy, and X-ray crystallography are widely used in the life sciences, material science, and medical diagnosis. High-quality and high-brightness X-rays are a strong requirement to improve applications. Inverse Compton scattering (ICS) X-ray source has attracted great interests worldwide lately. To significantly enhance the average X-ray photon flux, a compact electron storage-ring combined with a high finesse optical enhancement cavity (OEC) can be utilized. In such a system, the collision rate between the electron beam and the laser pulse is greatly increased to the MHz range, enabling a photon flux up to 10¹³ph/s.In the first chapter, I describe the motivation behind the development of OEC based on ICS X-ray source. The characteristics of this kind of X-ray source are summarized, compared to those of the conventional low-repetition-rate Terawatt laser system based on ICS X-ray source. The latest progress and research status of OEC based on ICS X-ray source are presented. Pulsed-laser injected high-finesse OEC stacking theory and properties are discussed in Chapter 2. Not only does the OEC based on ICS X-ray source require the laser pulse repetition rate to be matched to the free spectral range (FSR) of the cavity, where both also have to match the electron storage-ring circulation frequency. In addition, we have to match the phase shift of the laser repetition rate to the phase offset introduced by the dispersion of the cavity mirrors, since our cavity finesse design value is quite high. The stacking theory is analyzed in the frequency domain. Cavity properties, including cavity mirror dispersion, finesse, and FSR, are discussed in detail. A laser frequency comb and OEC coupling is analyzed also. The laser source development is presented in Chapter 3. We constructed a mode-locked fiber laser based on nonlinear polarization rotation. The locking model, locking techniques, and the theory, simulations and experimental tests of tilt locking (TL) in the pulsed laser injected high-finesse OEC are discussed in Chapter 4. We succeeded in locking a pulsed laser to a high-finesse cavity with the TL technique. The experimental results show that the TL and the Pound-Drever-Hall techniques have the same performance: stable locking, high sensitivity, and the same power coupling rate for picosecond laser pulse case, while the test results for full spectrum TL locking show that it is uneasy to align the split-photodiode to the beam waist.Based on the above experimental study and tests, we design the OEC system for Tsinghua University X-ray project in Chapter 5. The expected X-ray flux is 10¹º to 10¹³ ph/s. We detail every subsystem requirement.

Le sujet de cette thèse se rapporte à la génération d’impulsions ultracourtes dans une cavité laser fibrée à travers l’optimisation automatique de ses paramètres par un algorithme d’évolution. L’intérêt pour cette problématique provient de la difficulté à explorer les dynamiques impulsionnelles de manière systématique dans un large domaine de paramètres expérimentaux. Nous avons montré que l’implémentation d’un algorithme d’évolution sur une cavité laser fibrée de ce type peut être réalisée, en prenant les précautions adéquates pour que cette association soit la plus efficace possible. Nous avons démontré expérimentalement pour la première fois le verrouillage de modes depuis la seule optimisation des contrôleurs de polarisation utilisant une procédure automatique d’auto-apprentissage. Nous avons démontré que la sélection du blocage de modes depuis son spectre radio-fréquence permet de sélectionner le taux de répétition desimpulsions à l’intérieur de la cavité. Ces résultats préliminaires démontrent les potentialités de notre méthode employée dans des situations de dynamique non linéaire ultrarapide de grande complexité, particulièrement sensibles aux paramètres. / This thesis deals with the generation of ultrashort pulses within a fiber laser cavity through the automatic optimization of its parameters by an evolutionary algorithm. The interest of this subject comes from the difficulty to systematically explore dynamics in a large domain of experimental parameters. We have shown that it is possible to implement an evolutionary algorithm on fiber laser cavity with appropriate precautions. We have experimentally demonstrated for the first time the mode locking of a laser cavity only using the optimization of polarization controllers through an automatic and self-learning procedure. We also have demonstrated that selecting the mode locking from it radio-frequency spectrum allow to select the pulses repetition rate within the cavity. These preliminary results show the promising aspect of our method used in situations of non linear ultrafast dynamics with high complexity which are particularly sensitive to parameters.

Cette étude s’intéresse à l’amélioration des performances du laser solide Er3+:YAG, dont la longueur d’onde de 1,64 µm est dite « eye-safe ». L’une des solutions est le remplacement des monocristaux actuellement utilisés comme milieu amplificateur par des céramiques polycristallines Er:YAG transparentes, dont les propriétés thermomécaniques remarquables permettent une meilleure cohérence du faisceau de sortie et de ce fait, une augmentation des performances du laser. Cependant, la réunion des différents critères requis pour obtenir la transparence reste un réel challenge dans l’élaboration de ces céramiques. L’utilisation de poudres commerciales issues de deux voies de synthèse différentes a permis de souligner le rôle primordial des caractéristiques physiques de la poudre sur le comportement à la compaction et au frittage, effectué par Spark Plasma Sintering, tandis que la composition phasique et la pureté chimique conditionnent la qualité optique finale. Il ressort également que la coloration de la céramique observée lors du frittage résulte, non pas d’une contamination au carbone, mais de la formation de lacunes d’oxygène. Enfin, l’analyse et la compréhension du mode d’action du LiF utilisé comme aide au frittage ont permis d’établir des mécanismes réactionnels permettant d’optimiser le cycle de frittage. Cette démarche a conduit à l’obtention de céramiques polycristallines transparentes (Ø = 30 mm, e = 3 mm) à qualité optique élevée avec des valeurs de transmission de 80 % à 400 nm et 84 % à 1100 nm. Sur la base de ces résultats et de la simulation numérique, un changement d’échelle des céramiques (Ø = 50 mm, e = 5 mm) a été effectué dans le but de les évaluer en cavité laser. / This work focus on the improvement of the solid state Er3+:YAG laser performances presenting an "eye-safe" wavelength at 1.64 µm. One way is the replacement of single crystals currently used as gain media by polycrystalline ceramics as they present improved thermo-mechanical properties allowing a longer use of the laser. However, the meeting of different criteria requested to get transparency remains a challenge in the development of these ceramics. The use of commercial powders produced by two different synthesis ways allowed to highlight the essential role of the physico-chemical characteristics of the powder on compaction and sintering behaviors, performed by Spark Plasma Sintering, Phase composition and chemical purity have an influence of the final optical quality. It was also figured out that the gray coloration of the ceramic observed after sintering is caused by the formation of oxygen vacancies, rather than a carbon contamination. Finally, the mode of action of LiF, used as sintering aid to increase optical transmittance, was studied in order to establish reaction mechanisms allowing an optimization of the SPS cycle. This approach helps to reach Er3+:YAG transparent polycrystalline ceramics (Ø = 30 mm, thk = 3 mm) with an optical transmittance of 80 at 400 nm and 84 % at 1100 nm. On the basis of these results and with the help of numerical simulation, an up-scaling of ceramics (Ø = 50 mm, thk = 5 mm) was undertaken in order to evaluate their laser performances through laser cavity tests.