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Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-26T14:41:01Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) dissertacao luis giraldo.pdf: 10535616 bytes, checksum: 68be7b1f243dec018540fff871537861 (MD5) / Made available in DSpace on 2016-07-26T14:41:01Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) dissertacao luis giraldo.pdf: 10535616 bytes, checksum: 68be7b1f243dec018540fff871537861 (MD5) Previous issue date: 2014-12-11 / Lasers de pulsos ultracurtos baseados em fibras ópticas como meio de ganho constituem fortes candidatos para substituir lasers de estado sólido mais tradicionais, tais como o laser de Ti:safira. Uma das razões é o custo direto e outra é a possibilidade de compactação de sistemas que ocupam muito espaço e consomem quantidades significativas de energia. Um dos problemas de lasers baseados em fibras ópticas é que a potência óptica média disponível é relativamente baixa, da ordem de poucas dezenas de mW. Em nosso laboratório o interesse é em fazer uso de lasers em fibra pulsados para aplicações em metrologia óptica e óptica quântica e, em ambos os casos, as potências requeridas são maiores, indicando a necessidade de desenvolver um amplificador óptico. O sistema deve ser capaz de amplificar pulsos que incialmente têm duração da ordem de centenas de femtosegundos, taxa de repetição de centenas de MHz e energias por pulso da ordem de 1 pJ. Estes parâmetros indicam que o sistema deve operar num regime de forte saturação. Nesta dissertação serão descritos a construção e caracterização um amplificador óptico que faz uso de uma fibra dopada com érbio como meio de ganho. Foram testadas várias combinações de comprimento de fibra de ganho, comprimento de fibra de entrada e de saída que permitiram controlar os efeitos dispersivos e não lineares de forma a obter os maiores ganhos possíveis, mas mantendo a duração temporal dos pulsos amplificados dentro de uma faixa aceitável para as aplicações de interesse do laboratório. Com isto obtivemos um amplificador com um ganho de aproximadamente x15, com potências de entrada da ordem de 10 mW, mantendo a duração de pulso de saída do sistema da mesma ordem daquela do pulso de entrada. Estas características são satisfatórias para as aplicações em que o sistema será utilizado. / Ultrashort pulse laser based optical fiber as the gain medium are strong candidates to replace more traditional lasers solid state lasers such as Ti: sapphire. One reason is the direct cost and the other is the possibility of compression systems that take up much space and consume significant amounts of energy. One of the problems of lasers based on optical fibers is that the average optical power available is relatively low, of the order of a few tens of mW. In our laboratory interest is the use in pulsed fiber lasers for applications in quantum optics and optical metrology and, in both cases, the required powers are higher, indicating a need to develop an optical amplifier. The system should be able initially to amplify pulses that have a duration on the order of hundreds of femtoseconds, repetition rate of hundreds of MHz and pulse energies on the order of 1 pJ. These parameters indicate that the system should operate in a regime of strong saturation. This dissertation will be described the construction and characterization of an optical amplifier which makes use of an erbium doped fiber as the gain medium. Various combinations of gain fiber length, fiber length input and output control enabled dispersive and nonlinear effects in order to obtain the highest possible gains while maintaining the temporal duration of the amplified pulses within an acceptable range were tested for the applications of interest for the laboratory. With this we obtained an amplifier with a gain of about x15, with the input powers of about 10 mW, while maintaining the pulse duration of the output of the same order as that of the input pulse system. These features are suitable for applications where the system is used.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-26T15:07:25Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) dissertacao luis giraldo.pdf: 10535616 bytes, checksum: 68be7b1f243dec018540fff871537861 (MD5) / Made available in DSpace on 2016-07-26T15:07:25Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) dissertacao luis giraldo.pdf: 10535616 bytes, checksum: 68be7b1f243dec018540fff871537861 (MD5) Previous issue date: 2014-12-11 / Lasers de pulsos ultracurtos baseados em fibras ópticas como meio de ganho constituem fortes candidatos para substituir lasers de estado sólido mais tradicionais, tais como o laser de Ti:safira. Uma das razões é o custo direto e outra é a possibilidade de compactação de sistemas que ocupam muito espaço e consomem quantidades significativas de energia. Um dos problemas de lasers baseados em fibras ópticas é que a potência óptica média disponível é relativamente baixa, da ordem de poucas dezenas de mW. Em nosso laboratório o interesse é em fazer uso de lasers em fibra pulsados para aplicações em metrologia óptica e óptica quântica e, em ambos os casos, as potências requeridas são maiores, indicando a necessidade de desenvolver um amplificador óptico. O sistema deve ser capaz de amplificar pulsos que incialmente têm duração da ordem de centenas de femtosegundos, taxa de repetição de centenas de MHz e energias por pulso da ordem de 1 pJ. Estes parâmetros indicam que o sistema deve operar num regime de forte saturação. Nesta dissertação serão descritos a construção e caracterização um amplificador óptico que faz uso de uma fibra dopada com érbio como meio de ganho. Foram testadas várias combinações de comprimento de fibra de ganho, comprimento de fibra de entrada e de saída que permitiram controlar os efeitos dispersivos e não lineares de forma a obter os maiores ganhos possíveis, mas mantendo a duração temporal dos pulsos amplificados dentro de uma faixa aceitável para as aplicações de interesse do laboratório. Com isto obtivemos um amplificador com um ganho de aproximadamente x15, com potências de entrada da ordem de 10 mW, mantendo a duração de pulso de saída do sistema da mesma ordem daquela do pulso de entrada. Estas características são satisfatórias para as aplicações em que o sistema será utilizado. / Ultrashort pulse laser based optical fiber as the gain medium are strong candidates to replace more traditional lasers solid state lasers such as Ti: sapphire. One reason is the direct cost and the other is the possibility of compression systems that take up much space and consume significant amounts of energy. One of the problems of lasers based on optical fibers is that the average optical power available is relatively low, of the order of a few tens of mW. In our laboratory interest is the use in pulsed fiber lasers for applications in quantum optics and optical metrology and, in both cases, the required powers are higher, indicating a need to develop an optical amplifier. The system should be able initially to amplify pulses that have a duration on the order of hundreds of femtoseconds, repetition rate of hundreds of MHz and pulse energies on the order of 1 pJ. These parameters indicate that the system should operate in a regime of strong saturation. This dissertation will be described the construction and characterization of an optical amplifier which makes use of an erbium doped fiber as the gain medium. Various combinations of gain fiber length, fiber length input and output control enabled dispersive and nonlinear effects in order to obtain the highest possible gains while maintaining the temporal duration of the amplified pulses within an acceptable range were tested for the applications of interest for the laboratory. With this we obtained an amplifier with a gain of about x15, with the input powers of about 10 mW, while maintaining the pulse duration of the output of the same order as that of the input pulse system. These features are suitable for applications where the system is used.

I present several new methods for the characterisation of ultrashort pulses using interferometry. A generalisation of the concatenation algorithm for spectral shearing interferometry enables interferograms taken at multiple shears to be combined. This improves the precision of the reconstructed phase in the presence of detector noise, and enables the relative phase between disjoint spectral components to be obtained without decreasing the spectral resolution. The algorithm is applied to experimental data from two different implementations of spectral shearing interferometry for ultrashort optical pulses. In one, the shears are acquired sequentially, and in the other they are acquired simultaneously. I develop a form of spatio-temporal ultrashort pulse characterisation which performs both spatial and spectral shearing interferometry simultaneously. It requires a similar geometrical setup to common implementations of spectral phase interferometry for direct electric-field reconstruction, but provides complete amplitude and phase characterisation in time and one spatial dimension. I develop the theory of lateral shearing interferometry for spectrally resolved wavefront sensing of extended ultraviolet and soft x-ray pulses generated using high-harmonic generation. A comprehensive set of wavefront measurements of harmonics 13-25 in Krypton show good agreement with theory, validating the technique. I propose and numerically demonstrate quantum-path interferometry mediated by a weak control field for high harmonic generation. This is a general technique for measuring the amplitude and relative phases of each contributing quantum path. The control field perturbatively modulates the phase of each path. The differing sensitivity of each path to the parameters of the control field allows their contributions to be distinguished from one another.

Les lasers de haute puissance permettent d'atteindre des intensités très importantes (jusqu'à 10²²W.cm⁻²). Parvenir à ce niveau d'intensité nécessite de concentrer une quantité modérée d'énergie (de l'ordre du joule) dans un temps très court (de l'ordre de la dizaine de femtosecondes) sur une surface réduite (de l'ordre du μm²). Ces faisceaux sont donc ultra-courts et focalisés à l'aide d'une optique à grande ouverture. Ces caractéristiques signifient que leur diamètre avant focalisation est grand et leur largeur spectrale est importante. Pour cette raison, ces faisceaux sont à même de présenter des distorsions spatio-spectrales (ou couplages spatio-temporels). Après focalisation, ces distorsions ont pour effet une diminution drastique de l'intensité pic. Ceci est d'autant plus vrai que le système laser est puissant et donc que son diamètre et sa largeur spectrale sont grands. En dépit de cet effet néfaste, les couplages spatio-temporels présentent aussi un intérêt lorsqu'ils sont maitrisés. On peut en effet introduire des couplages spatio-temporels de faible amplitude à des fins expérimentales. Dans les années 1990 et 2000, un effort important a été fourni pour permettre la caractérisation et l'optimisation du profil temporel des lasers femtoseconde. Dans le même temps, des solutions d'optique adaptative ont été développées pour contrôler le profil spatial des faisceaux ultra-intenses et obtenir la meilleure tache focale possible. Les systèmes laser de haute-puissance actuels sont maintenant caractérisés et optimisés indépendamment par ces deux types de diagnostics. Par essence, cette approche est aveugle aux couplages spatio-temporels. Seule une caractérisation spatio-temporelle permettrait de mesurer ces distorsions. Il existait déjà des méthodes de caractérisation spatio-temporelle avant le début de cette thèse. Aucun de ces dispositifs n'avait cependant été adapté à la mesure de faisceaux ultra-intenses. Lors de cette thèse, nous avons développé une nouvelle technique de caractérisation spatio-temporelle appelée TERMITES. Cette technique est basée sur un schéma de spectroscopie par transformée de Fourier auto-référencée. TERMITES nous a permis d'effectuer la première caractérisation spatio-temporelle totale d'un laser 100 TW (le laser UHI-100 du CEA Saclay). Les distorsions spatio-temporelles détectées à l'aide de ces mesures ont confirmé la nécessité d'une généralisation de la métrologie spatio-temporelle des lasers de haute puissance. / High power laser make it possible to reach very high intensities (up to 10²²W.cm⁻²). In order to get to this level of intensity, a moderate quantity of energy (on the order of the Joule) is concentrated in a very short time (on the order of tens of femtoseconds) onto a small surface (on the order of 1 μm²). These beams are therefore ultra-short and focused with a high aperture optic. These features mean that their diameter prior to focus is large and their spectral width is big. As a result, these beams are subject to spatio-spectral distorsions (of spatio-temporal couplings). After focus, these distorsions induce a dramatic reduction of the peak intensity. This situation is all the more true when the laser is more intense and its diameter and spectral width are therefore bigger. Despite their detrimental effects, spatio-temporal couplings can be of great interest when controlled. One can indeed introduce weak spatio-temporal couplings for experimental purposes. In the 1990s and 2000s, a big effort was put in order to characterize dans optimize the temporal profile of femtosecond lasers. Meanwhile, adaptative optics solutions were developed to control the spatial profil of ultra intense laser beams and provide the best focal spot achievable. By nature, this approach is blind to spatio-temporal couplings. Measuring these distorsions requires a spatio-temporal characterization. Before the start of this Phd thesis, spatio-temporal characterization methods already existed. Although none of these devices were ever adapted to the measurement of ultra-intense laser beams. During this Phd Thesis, we developped a new spatio-temporal characterization technique which we called TERMITES. This technique is based on a self-referenced Fourier transform spectroscopy scheme. TERMITES made it possible for us to perform the first total spatio-temporal characterization of a 100 TW laser (UHI-100 at CEA Saclay, France). The detection of spatio-temporal distorsions with the help of these measurements confirmed the need for a generalization of spatio-temporal characterization of ultra-high power lasers.