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Gapontsev, Denis Valentinovitch. "Fiber Raman lasers and amplifiers and their applications". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322403.
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Berberoglu, Halil. "Numerical Simulations On Stimulated Raman Scattering For Fiber Raman Amplifiers And Lasers Using Spectral Methods". Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608986/index.pdf.
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Optical amplifiers and lasers continue to play its crucial role and they have become an indispensable part of the every fiber optic communication systems being installed from optical network to ultra-long haul systems. It seems that they will keep on to be a promising future technology for high speed, long-distance fiber optic transmission systems.
The numerical simulations of the model equations have been already commercialized by the photonic system designers to meet the future challenges. One of the challenging problems for designing Raman amplifiers or lasers is to develop a numerical method that meets all the requirements such as accuracy, robustness and speed.
In the last few years, there have been much effort towards solving the coupled differential equations of Raman model with high accuracy and stability. The techniques applied in literature for solving propagation equations are mainly based on the finite differences, shooting or in some cases relaxation methods. We have described a new method to solve the nonlinear equations such as Newton-Krylov iteration and performed numerical simulations using spectral methods. A novel algorithm implementing spectral method (pseuodspectral) for solving the two-point boundary value problem of propagation equations is proposed, for the first time to the authors'knowledge in this thesis. Numerical results demonstrate that in a few iterations great accuracy is obtained using fewer grid points.
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Zhu, Gongwen. "Q-switched and Mode-locked Mid-IR Fiber Lasers". Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/578593.
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Mid-infrared (IR) lasers (2-12 μm) have found tremendous applications in medical surgeries, spectroscopy, remote sensing, etc. Nowadays, mid-IR emissions are usually generated from semiconductor lasers, gas lasers, and solid-state lasers based on nonlinear wavelength conversion. However, they usually have disadvantages including poor beam quality, low efficiency, and complicated configurations. Mid-IR fiber lasers have the advantages of excellent beam quality, high efficiency, inherent simplicity, compactness, and outstanding heat-dissipating capability, and have attracted significant interest in recent years. In this dissertation, I have studied and investigated Q-switched and mode-locked fiber lasers in the mid-IR wavelength region. My dissertation includes six chapters: In Chapter 1, I review the background of mid-IR lasers and address my motivation on the research of mid-IR fiber lasers; In Chapter 2, I present the experimental results of microsecond and nanosecond Er³⁺-doped and Ho³⁺-doped fiber lasers in the 3 μm wavelength region Q-switched by Fe²⁺:ZnSe and graphene saturable absorbers. In Chapter 3, Q-switched 3 μm laser fiber amplifiers are investigated experimentally and theoretically and their power scaling are discussed. In Chapter 4, a graphene mode-locked Er³⁺-doped fiber lasers at 2.8 μm with a pulse width < 50 ps is presented. In Chapter 5, extending the spectral range of mid-IR fiber lasers by use of nonlinear wavelength conversion is addressed and discussed. I have proposed 10-watt-level 3-5 μm Raman lasers using tellurite fibers as the nonlinear gain medium and pumped by our Er³⁺-doped fiber lasers at 2.8 μm. In the last chapter, the prospect of mid-IR fiber laser is addressed and further research work is discussed.
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El, bassri Farid. "Sources lasers déclenchées nanosecondes : Applications à la spectroscopie Raman cohérente sous champ électrique". Thesis, Limoges, 2014. http://www.theses.fr/2014LIMO0060/document.
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Du fait de leur compacité, leur robustesse et leur faible coût, les microlasers impulsionnels nanosecondes constituent des sources particulièrement attractives pour de nombreux systèmes de détection et d'analyse, en particulier les cytomètres en flux ou les dispositifs pour la spectroscopie CARS (Coherent Raman Anti Stokes Scattering). Cependant, ces applications nécessitent des performances améliorées en ce qui concerne la gigue temporelle et la cadence de répétition accessible. Dans sa première partie, cette thèse propose des solutions originales pour atteindre les performances requises à partir de microlasers passivement déclenchés, grâce à la mise en oeuvre d'une cavité hybride couplée, pompée par une onde modulée en intensité. Une cadence de répétition supérieure à 30 kHz avec une gigue demeurant inférieure à 200 ns est atteinte. Le potentiel de microlasers à fibres déclenchés par modulation du gain pour monter en cadence est aussi évalué, montrant que des impulsions à faible gigue, à une cadence de plus de 2 MHz peuvent être produites. Enfin, la dernière partie est consacrée à la mise au point et à l'exploitation d'un nouveau système de spectroscopie CARS assisté par une excitation électrique haute tension. Ce dispositif, réalisé à partir d'un microlaser amplifié, permet de s'affranchir du bruit de fond non résonnant des mesures et de réaliser une analyse spectroscopique fine de la réponse de différents milieux d'intérêt sous champ continu ou impulsionnel, pouvant conduire à une nouvelle méthode de microdosimétrie de champ. Diverses applications, dont la granulométrie à l'échelle micro ou nanométrique ou l'identification de marqueurs pour la biologie, sont démontréesThanks to their compactness, robustness and low cost, pulsed nanosecond microlasers are particularly attractive sources for different detection and analysis systems, particularly flow cytometers or devices for CARS (Coherent Anti Raman Stokes Scattering) spectroscopy. However, these applications require reduced time jitter and increased repetition rate. The first part of this thesis proposes novel solutions to achieve the required performance from passively Q-switched microlasers, which are based on an hybrid coupled-cavity and intensitymodulated pump wave. A repetition rate greater than 30 kHz with jitter remaining lower than 200 ns is reached. Pulsed fiber microlasers operating by gain switching are also studied, showing that pulses with low timing jitter, at a repetition rate of more than 2 MHz can be obtained. The last part is devoted to the development and the implementation of a new system of CARS spectroscopy assisted by a high-voltage electrical stimulation. This device, based on an amplified microlaser, allows to substract the non-resonant background noise in the measurements. Thus, a fine spectroscopic analysis of the response of different environments of interest in continuous or pulsed field can be achieved. It may lead to a new method for field microdosimetry. Various applications, including granulometry at the micro or nanometric scale and the identification of markers for biology, are shown
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Nishizawa, Norihiko, Youta Ito i Toshio Goto. "0.78-0.90-μm wavelength-tunable femtosecond soliton pulse generation using photonic crystal fiber". IEEE, 2002. http://hdl.handle.net/2237/6769.
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Benoit, Aurélien. "Sources laser fibrées hybrides de haute puissance : Amplification et conversion de fréquences". Thesis, Limoges, 2015. http://www.theses.fr/2015LIMO0024/document.
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Les lasers à fibre de haute puissance constituent depuis une dizaine d’année un outil pertinent pour un nombre croissant d’applications. Dans le cadre d’un contrat CIFRE entre la société Eolite Systems et le laboratoire Xlim (UMR 7252 du CNRS et de l’Université de Limoges), mon projet de thèse a consisté à développer les briques technologiques de futures sources lasersHigh-power fiber lasers adress an increasing number of applications since ten years. In the frame of a CIFRE contract between the company Eolite Systems and Xlim (joint laboratory between CNRS and the University of Limoges), the goal of this PhD project was to develop the technological blocs to achieve all-fibre high-power lasers emiting out of the conventional spectral band covered by existing lasers.Modal instabilities in large mode area (LMA) fibers are currently the main limitation of the fiber lasers power scaling. We have experimentally demonstrated the relevance of inner cladding aperiodic structures to efficiently delocalize higher order modes outside the gain region. A systematic study of passive fibers based on such structures has shown the single propagation of the fundamental mode over a wide wavelength range from 1 to 2 µm for dimension of core up to 85 µm. This effective mode delocalization even extends up to a core dimension of 140 µm at a 2 µm wavelength.The combination of high power picosecond fiber laser with an average power of 22.7 W and a hydrogen-filled inhibited coupling Kagome fiber allowed us to generate two Raman combs over five frequency octaves from 321 nm to 12.5 µm. These two combs are controlled by the laser pump polarization and generated an average power of 10.1 W displayed over 70 laser lines for circular pump polarization and 8.6 W over 30 lines for linear polarization. Some laser lines within these combs have been generated for the first time from high-power fiber source in the mid-infrared range. We have also demonstrated the generation of high-power line by optimizing the first vibrational Stokes at 1.8 µm with an average power of 9.3 W and a quantum efficiency of the frequency conversion stage close to 80%
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Louot, Christophe. "Sources de supercontinuum pour la microspectroscopie Raman cohérente large-bande". Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0015/document.
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La microspectroscopie Raman cohérente (CARS) est une méthode d'analyse optique sans marqueur qui permet d'identifier des liaisons moléculaires dans un milieu d'intérêt (échantillon) pour permettre de déterminer la composition chimique de ce milieu. Elle nécessite l'excitation concomitante de l'échantillon par deux ondes spectralement décalées (onde pompe et onde Stokes) afin de faire entrer en résonance les liaisons à détecter. Pour la détection de plusieurs liaisons simultanément (microspectroscopie Raman cohérente large-bande ou Multiplex-CARS), la source Stokes monochromatique est remplacée par une source laser large-bande (supercontinuum). Les travaux effectués dans le cadre de cette thèse visent à proposer de nouvelles sources de supercontinuum émettant des faisceaux optimisés en termes d'élargissement spectral et de densité spectrale de puissance pour la microspectroscopie Multiplex-CARS. Pour ce faire, les moyens de développer des continuums spectraux performants ont été explorés dans trois fibres optiques différentes: une fibre microstructurées air/silice monomode à gros cœur dopé à l'ytterbium permettant une réamplification du signal tout au long de sa propagation ; une fibre monomode conventionnelle en régime de dispersion normale pour obtenir un élargissement spectral par saturation du gain Raman ; une fibre multimode dans laquelle le faisceau spectralement élargi par saturation du gain Raman à très forte puissance subit également un auto-nettoyage spatial par effet Kerr tout au long de sa propagation, produisant en sortie un faisceau de forte brillance dont le profil d’intensité est semblable à celui du mode fondamental. Une étude spectrotemporelle complète est présentée pour ces trois sourcesCoherent Raman microspectroscopy (CARS) is an optical method used to identify molecular bonds in a sample in order to analyze and determine its complete composition. It requires the simultaneous excitation of the sample by two waves (the pump wave and the Stokes wave) in order to induce resonant vibration of the bond to be detected. For multiple bonds analysis (broadband coherent Raman microspectroscopy our Multiplex-CARS), the monochromatic Stokes wave must be replaced by a broadband beam (supercontinuum). The aim of this thesis was to design supercontinuum sources optimized for Multiplex-CARS application, in particular in terms of spectral bandwidth and spectral power density. Supercontinuum generation was investigated in three different optical fibers: (i) a microstructured single mode fiber with a large Yb doped core in which the input beam was re-amplified all along its propagation; (ii) a conventional singlemode fiber pumped in the normal dispersion regime in which spectral broadening was achieved by means of Raman gain saturation; (iii) a conventional graded-index multimode fiber in which the beam spectrally broadened by Raman gain saturation at very high power also experienced spatial self-cleaning by Kerr effect, resulting in a high brillance output beam with an,intensity profile close to that of the fundamental mode. A complete spectrotemporal study is achieved for each of these three sources
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Nishizawa, Norihiko, i Toshio Goto. "Widely wavelength-tunable ultrashort pulse generation using polarization maintaining optical fibers". IEEE, 2001. http://hdl.handle.net/2237/6864.
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Nishizawa, Norihiko, i Toshio Goto. "Compact system of wavelength-tunable femtosecond soliton pulse generation using optical fibers". IEEE, 1999. http://hdl.handle.net/2237/6767.
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Nishizawa, Norihiko, Ryuji Okamura i Toshio Goto. "Simultaneous generation of wavelength tunable two-colored femtosecond soliton pulses using optical fibers". IEEE, 1999. http://hdl.handle.net/2237/6771.
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Alsaleh, Magda. "Application de la méthode des coordonnées collectives à l'analyse de la dynamique des lasers à fibre à modes bloqués". Thesis, Dijon, 2015. http://www.theses.fr/2015DIJOS091/document.
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Les lasers à fibres à modes bloqués font partie des rares systèmes qui permettent de réaliser une variété de fonctions optiques élaborées, au moyen de peu de composants optiques. La gestion de la dispersion apporte à ce type de lasers une variété de comportements, qui est si riche que la cartographie complète et l’analyse détaillée des états stables deviennent difficilement réalisable lorsqu’on utilise les outils conventionnels basés sur les équations de propagation du champ intra-cavité. Dans cette thèse nous montrons que l’adjonction de la technique des coordonnées collectives aux outils théoriques conventionnels, permet de résoudre au moins en partie le problème de la complexité et l’extrême diversité des états stables des cavités gérées en dispersion. En particulier, nous proposons l’ACCD (approche des coordonnées collectives dynamiques), comme un outil théorique permettant de réaliser des gains de performance substantiels dans des opérations de recherche et caractérisation des états stables du laser. D’autre part, le recours à l’approche des cordonnées collectives nous permet de mettre en évidence des effets majeurs induits par certains phénomènes qui étaient jusqu’à présent largement sous-estimés. Notamment, nous mettons en évidence des modifications majeures desdomaines respectifs des différents états stables du laser, qui surviennent lorsqu’on change la bande passant de la fitre. D’autre part, en considérant une cavité où la largeur spectrale du champ lumineux (3.12 THz) est d’un ordre de grandeur plus petite que la largeur de la bande du gain Raman, nous mettons en lumière des effets remarquables de la diffusion Raman sur les phénomènes d’hystérésisMode-locked fiber laser are among the few systems that allow to achieve a variety of elaborate optical functions, by means of few optical components. The use of dispersion management brings to this type of lasers a variety of behaviors, which is so rich that the complete mapping and detailed analysis of the stable states becomes impractical when conventional tools based on the intra-cavity field propagation equations, are used. In this thesis we show that the addition of the technique ofcollective coordinates to the conventional theoretical tools, allows to solve at least in part the problem of complexity and diversity of the stable states of the cavity. In particular, we propose the DCCA (dynamical collective coordinate approach), as a theoretical tool to achieve substantial performance gains in search and characterization of stable states of the laser. Furthermore, the use of the collective coordinated approach allows us to highlight major effects induced by certain phenomena that were until now largely underestimated. In particular, we highlight major changes in the respective areas ofthe different stable states of the laser, which occur when changing the width of the band-pass filter BPF. Furthermore, considering a cavity where the spectral width of the light field (3.12 THz) is an order of magnitude smaller than the bandwidth of the Raman gain, we highlight remarkable effects of Raman scattering on hysteresis phenomena
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Chafer, Matthieu. "Sources lasers innovantes à base de micro-capsules photoniques et par nano-structuration de milieux gazeux". Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0042.
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Depuis leur avènement, les fibres à cristal photonique à cœur creux ont prouvé leur capacité à convertir des fréquences avec une haute efficacité, notamment en jouant sur le phénomène de diffusion Raman stimulée. Dans le cadre d’un contrat CIFRE entre la société GLOphotonics et l’institut de recherche Xlim, ce projet de thèse a consisté à développer ces fibres afin d’améliorer leurs performances optiques pour cibler deux voies d’applications: une industrielle pour proposer un laser compact multi-ligne dans le visible et dans l’UV et une seconde plus fondamentale pour réaliser un synthétiseur d’onde optique. L’amélioration de ces performances repose sur l’exacerbation de l’inhibition du couplage entre le mode du coeur d’air et les modes de silice de la gaine. Pour cela deux types de micro-structures ont été explorées à savoir une maille Kagomé et une maille tubulaire. Plusieurs fibres ont été alors fabriquées démontrant des performances records sur toute une gamme de longueurs d’onde (8,5 dB/km à 1 µm, 7,7 dB/km à 750 nm, 13,8 dB/ km à 549 nm, et autour de 70 dB/km à 355 nm). Concernant la fonctionnalisation de ces fibres, des micro-capsules photoniques ont été conçues et réalisées permettant à la fois de palier au problème de la perméabilité de la silice au gaz (stabilité de la conversion dépassant 12 mois) et de démontrer une conversion de 26 lignes dans le visible. Un produit industriel nommé CombLas a alors été produit puis appliqué à une étude de cytométrie en flux pour étudier l’influence du taux de répétition du laser de pompe. Ce produit a également été étendu à la gamme spectrale de l’UV avec la génération de 24 lignes entre 225-400 nm. Enfin, des travaux plus fondamentaux ont été réalisés consistant à développer un synthétiseur d’onde optique à base de génération Raman dans ces fibres creuses. Une nouvelle dynamique a été observée démontrant le piégeage de molécules d’hydrogène par un réseau optique auto-assemblé de puits de potentiel ultra-profonds et nanométriques. Cela permis de générer un régime Lamb-Dicke de la diffusion Raman stimulée. Des signatures sub-Doppler usuellement vues dans les atomes froids ont été mesurées avec des largeurs de bandes plus étroites de plus de 5 ordres de grandeurs par rapport à ce qui est prédit dans la littérature. Finalement, cette largeur de bande a été optimisée d’un ordre de grandeur en jouant sur la longueur de la fibre et la pression de l’hydrogèneSince their advent, hollow-core photonic crystal fibers have proved to be highly efficient for frequency conversion, especially via by playing with stimulated Raman scattering. Within the frame work of a CIFRE contract between the firm GLOphotonics and the Xlim research institute, this thesis project has consisted in developing these fibers to enhance their optical performances, in order to target two different field of applications: an industrial one to offer a a compact multi-line laser in the visible and UV and a second more fundamental one to realize a optical wave synthesizer. The amelioration of these performances relies on the exacerbation of the inhibition of the coupling between the air core mode and the silica cladding modes. Two types of micro-structures have been explored, a Kagomé and a tubular lattice. Several fibers have been fabricated demonstrating record performances on all a wavelength range (8.5 dB/km at 1 µm, 7.7 dB/km at 750 nm, 13.8 dB/km at 549 nm, and around 70 dB/km at 355 nm). Concerning the functionalization of the fibers, photonic micro-cells have been designed and realized enabling to overcome the problem the permeability of silica to gas (conversion stability over 12 months) and demonstrate a conversion to 26 lines in the visible. An industrial product coined CombLas has been made and used for flow cytometry in order to study the influence of the repetition rate of the pump laser. This product has also been extended to the UV range with 24 lines generated between 225-400 nm. Also, more fundamental research has been realized consisting in developing an optical wave synthesizer based on Raman generation in hollow core fibres where a new dynamic has been observed demonstrating the trapping of hydrogen molecules by an auto-assembled optical lattice of ultra-deep and nano-metric potential wells. This configuration has enabled to generate a Lamb-Dicke regime of stimulated Raman scattering. Sub-Doppler signatures usually found in cold atoms have been measured with linewidths narrower than 5 orders of magnitude than what is predicted in the literature. Finally, this linewidth has been optmised of an order of magnitude by plaing on the length of the fiber and the pressure of hydrogen
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Ji, Junhua. "Cladding-pumped Raman fibre laser sources". Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/186035/.
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In this thesis, I investigate cladding-pumped Raman fibre lasers and amplifiers. Such devices, offering a novel way to generate Raman gain, combine the advantages of the hugely successful cladding-pumped rare-earth doped fibre lasers with those of stimulated Raman scattering. They not only inherit most advantages of conventional fibre devices, such as flexibility, high efficiency, compactness, and robustness, but also provide their own advantages and distinct properties relative to conventional fibre sources, i.e., wavelength flexibility and nearly instantaneous gain without energy storage. Cladding-pumped Raman fibre laser sources utilise double-clad Raman fibres as the gain medium. These are similar to a rare-earth doped double-clad fibre except that there is no laserion doping of the core. With double-clad fibres, the high-power output from low-cost multimode pump sources can be converted into diffraction-limited signal beams, e.g., through stimulated Raman scattering. Thus, cladding-pumped Raman fibre laser sources are a kind of brightness enhancers. In the beginning of this thesis, I theoretically analyse various factors that limit the brightness enhancement of such devices. One of the limits is unwanted 2nd-Stokes generation, which restricts the area ratio between the inner cladding and core. By designing a new DCRF with a W-type core, I successfully relax this restriction by nearly five times. Combined with other factors, i.e., core damage threshold, walk-off, numerical aperture, and background loss, a brightness enhancement of more than 3500 for the designed fibre could be achieved in such devices shown by a model with right pump sources and parameters. Secondly, I focus on the conversion efficiency of such devices. A well-designed fibre with inner-cladding-to-core area ratio around six was used as a double-clad Raman fibre, pumped by a source with nearly rectangular pulse shapes. The nearly rectangular pulses were obtained from an erbium and ytterbium co-doped master optical power oscillator through prepulse shaping. A sufficiently short piece was chosen to reduce the background loss and walk-off. The highest peak power conversion into the 1st Stokes was 75% and the energy conversion efficiency was over 60% in a pulsed cladding-pumped Raman fibre amplifier. Thirdly, I study the power scalability. Theoretically, I analyse the achievable power of such devices. The core size turns out to be a critical factor in most cases. The ultimately output power is limited to around 24 kW by thermal lensing if the core is large enough and enough pump power available. Experimentally, in collaboration with co-workers, a 100 W claddingpumped Raman fibre laser was demonstrated at 1116 nm. The output beam was nearly diffraction-limited. It shows the potential of power scalability of such devices and the ability of generating high power diffraction-limited sources at wavelengths outside the conventional range that rare-earth doped fibres offer. Since a large core size is a critical factor for power scaling, new double-clad Raman fibres with large-mode areas were introduced. They were experimentally demonstrated to work as efficiently as the previous fibre. An Nd:YAG laser was used to pump one of these fibres, and a 1 mJ Raman fibre source with good beam quality was thus demonstrated. This shows that double-clad Raman fibres offer another approach to obtaining high-brightness high-energy sources. In addition, based on a cladding-pumped Raman fibre converter, a simple and efficient method was proposed to generate supercontinuum sources.
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Alcon, Camas Mercedes. "Applications of ultralong Raman fibre lasers in photonics". Thesis, Aston University, 2011. http://publications.aston.ac.uk/15795/.
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This thesis presents a numerical and experimental investigation on applications of ultralong Raman fibre lasers in optical communications, supercontinuum generation and soliton transmission. The research work is divided in four main sections. The first involves the numerical investigation of URFL intra-cavity power and the relative intensity noise transfer evolution along the transmission span. The performance of the URFL is compared with amplification systems of similar complexity. In the case of intracavity power evolution, URFL is compared with a first order Raman amplification system. For the RIN transfer investigation, URFL is compared with a bi-directional dual wavelength pumping system. The RIN transfer function is investigated for several cavity design parameters such as span length, pump distribution and FBG reflectivity. The following section deals with experimental results of URFL cavities. The enhancement of the available spectral bandwidth in the C-band and its spectral flatness are investigated for single and multi-FBGs cavity system. Further work regarding extended URFL cavity in combination with Rayleigh scattering as random distributed feedback produced a laser cavity with dual wavelength outputs independent to each other. The last two sections relate to URFL application in supercontinuum (SC) generation and soliton transmission. URFL becomes an enhancement structure for SC generation. This thesis shows successful experimental results of SC generation using conventional single mode optical fibre and pumped with a continuous wave source. The last section is dedicated to soliton transmission and the study of soliton propagation dynamics. The experimental results of exact soliton transmission over multiple soliton periods using conventional single mode fibre are shown in this thesis. The effect of the input signal, pump distribution, span length and FBGs reflectivity on the soliton propagation dynamics is investigated experimentally and numerically.
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Zhou, Renjie. "Developments of Narrow-Linewidth Q-switched Fiber Laser, 1480 nm Raman Fiber Laser, and Free Space Fiber Amplifier". Thesis, The University of Arizona, 2011. http://hdl.handle.net/10150/202931.
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In the first chapter, a Q-switched fiber laser that is capable of generating transform-limited pulses based on single-frequency fiber laser seeded ring cavity is demonstrated. The output pulse width can be tuned from hundreds of nanoseconds to several microseconds. This Q-switched ring cavity fiber laser can operate over the whole C-band. In addition, a theoretical model is developed to numerically study the pulse characteristics, and the numerical results are in good agreements with the experimental results. In the next chapter, a Raman fiber laser is developed for generating signal at 1480 nm. Initial experimental results has demonstrated generating of Raman laser at 1175 nm, 1240 nm, 1315 nm, and 1395 nm wavelength. Finally, a free space fiber amplifier is studied both theoretically and experimentally. The experimental work has demonstrated signal coupling efficiency up to 90% in the NP highly Er/Yb co-doped phosphate fiber.
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Tiwari, Vidhu Shekhar. "DEVELOPMENT OF FIBER OPTIC SENSOR BASED ON LASER RAMAN SPECTROSCOPY". MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-07082008-143038/.
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Laser Raman Spectroscopy (LRS) has received worldwide acknowledgement as a powerful molecular finger print technique. The Raman spectrum of sample contains useful information such as molecular identity, composition, constituents concentration ratio etc. These information are manifested in the Raman spectrum in band heights, peak wavelength, band areas etc. The basis of quantitative analysis in Raman spectroscopy lies in the measurement of Raman band intensity, which is linearly dependent upon the sample concentration. On the other hand, Raman spectroscopy can also yield the qualitative information of samples by exhibiting bands corresponding to various chemical constituents in the sample mixture. The potentiality of Raman spectroscopy to perform quantitative as well as qualitative analysis of samples has been exploited in the development of Raman sensors in conjugation with the techniques of fiber optics. The main focus of the presented doctoral work is to realize a fiber optic Raman sensor to monitor the quality of liquid oxygen (LO2) in a rocket engine feed line. In this research investigation, I have shown how a bulk experimental configuration can be transformed to miniaturized prototype sensor, which is equally capable to determine the ratio of liquid oxygen and liquid nitrogen in their cryogenic mixture. This research was extended to monitor the concentration of oxygen and nitrogen in their gaseous mixture. Further, I have demonstrated that the Raman spectroscopy has the potentiality to measure the temperature of hydrogen in a laboratory environment by monitoring the variation in Raman rotation-vibrational line of hydrogen gas with temperature. Finally, I have experimentally studied the surface enhanced Raman spectroscopy (SERS) of silver colloidal solution, which is another interesting branch of Raman spectroscopy that has transcended the limitation of very low Raman cross-section to offer more insight to the chemical properties of samples.
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Dalloz, Nicolas. "Formation du spectre optique dans les lasers Raman à fibre". Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2011. http://tel.archives-ouvertes.fr/tel-00628627.
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Le travail présenté dans ce mémoire s'inscrit dans la problématique générale de la formation du spectre optique dans les lasers Raman à fibre. Nous avons mené une étude expérimentale sur un laser Raman à fibre oscillant dans une cavité Pérot-Fabry fermée par des miroirs de Bragg. Cette étude montre que la forme du spectre optique diffère selon la puissance du laser. En développant différents modèles, nous avons montré que les miroirs de Bragg sont à l'origine de ce changement de forme du spectre optique. En particulier, à faible puissance, la forme asymétrique du spectre provient d'effets dispersifs lors de la réflexion sur les miroirs de Bragg. A forte puissance, ces effets dispersifs sont dominés par les effets de filtrage des miroirs, ce qui conduit à la symétrisation du spectre du laser observée dans notre expérience. Par ailleurs, nous avons également étudié numériquement la statistique du champ Stokes intracavité. Nous avons montré que celle-ci change fortement selon que l'onde Stokes est incidente ou réfléchie par les miroirs de Bragg. Ce résultat nous a permis de questionner la validité d'un modèle récemment publié sur la formation du spectre optique du laser Raman à fibre. Ce modèle s'appuie sur les outils de la théorie cinétique des ondes, valable uniquement dans le cas de champs possédant une statistique gaussienne. Toutefois, notre étude numérique indique que cette condition n'est pas respectée dans le laser Raman à fibre, et la forme du spectre optique observé dans notre étude expérimentale s'oppose fortement à celle prédite par cette approche statistique de la formation du spectre optique du laser Raman à fibre.
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Tan, Mingming. "Raman fibre laser based amplification in coherent transmission systems". Thesis, Aston University, 2016. http://publications.aston.ac.uk/28899/.
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The thesis presents a detailed study of different Raman fibre laser (RFL) based amplification techniques and their applications in long-haul/unrepeatered coherent transmission systems. RFL based amplifications techniques were characterised from different aspects, including signal/noise power distributions, relative intensity noise (RIN), mode structures of induced Raman fibre lasers, and so on. It was found for the first time that RFL based amplification techniques could be divided into three categories in terms of the fibre laser regime, which were Fabry-Perot fibre laser with two FBGs, weak Fabry-Perot fibre laser with one FBG and very low reflection near the input, and random distributed feedback (DFB) fibre laser with one FBG. It was also found that lowering the reflection near the input could mitigate the RIN of the signal significantly, thanks to the reduced efficiency of the Stokes shift from the FW-propagated pump. In order to evaluate the transmission performance, different RFL based amplifiers were evaluated and optimised in long-haul coherent transmission systems. The results showed that Fabry-Perot fibre laser based amplifier with two FBGs gave >4.15 dB Q factor penalty using symmetrical bidirectional pumping, as the RIN of the signal was increased significantly. However, random distributed feedback fibre laser based amplifier with one FBG could mitigate the RIN of the signal, which enabled the use of bidirectional second order pumping and consequently give the best transmission performance up to 7915 km. Furthermore, using random DFB fibre laser based amplifier was proved to be effective to combat the nonlinear impairment, and the maximum reach was enhanced by >28% in mid-link single/dual band optical phase conjugator (OPC) transmission systems. In addition, unrepeatered transmission over >350 km fibre length using RFL based amplification technique were presented experimentally using DP-QPSK and DP-16QAM transmitter.
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Tarasov, Nikita. "Temporal and spatio-temporal regimes of generation of Raman fibre lasers". Thesis, Aston University, 2016. http://publications.aston.ac.uk/28851/.
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Temporal dynamics of Raman fibre lasers tend to have very complex nature, owing to great cavity lengths and high nonlinearity, being stochastic on short time scales and quasi-continuous on longer time scales. Generally fibre laser intensity dynamics is represented by one-dimensional time-series, which in case of quasi-continuous wave generation in Raman fibre lasers gives little insight into the processes underlying the operation of a laser. New methods of analysis and data representation could help to uncover the underlying physical processes, understand the dynamics or improve the performance of the system. Using intrinsic periodicity of laser radiation, one dimensional intensity time series of a Raman fibre laser was analysed over fast and slow variation time. This allowed to experimentally observe various spatio-temporal regimes of generation, such as laminar, turbulent, partial mode-lock, as well as transitions between them and identify the mechanisms responsible for the transitions. Great cavity length and high nonlinearity also make it difficult to achieve stable high repetition rate mode-locking in Raman fibre lasers. Using Faraday parametric instability in extremely simple linear cavity experimental configuration, a very high order harmonic mode-locking was achieved in ò.ò kmlong Raman fibre laser. The maximum achieved pulse repetition rate was 12 GHz, with 7.3 ps long Gaussian shaped pulses. There is a new type of random lasers – random distributed feedback Raman fibre laser, which temporal properties cannot be controlled by conventionalmode-locking or Q-switch techniques and mechanisms. By adjusting the pump configuration, a very stable pulsed operation of random distributed feedback Raman fibre laser was achieved. Pulse duration varied in the range from 50 to 200 μs depending on the pump power and the cavity length. Pulse repetition rate scaling on the parameters of the system was experimentally identified.
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Doutte, Anne. "Étude expérimentale et théorique de la dynamique des lasers Raman à fibre optique". Lille 1, 2005. http://www.theses.fr/2005LIL10158.
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Le laser Raman a été réalisé dans les années 70. Cependant la configuration ne permettait pas de l'utiliser à des fins industrielles. Il a fallu attendre les années 90, avec l'arrivée des diodes laser et des réseaux de Bragg pour que la configuration de ce laser évolue vers un système "tout fibre" utilisables dans des applications industrielles. Cependant pour rendre ce système vraiment attractif, la puissance de sortie doit être stable. C'est dans ce contexte que se situe ce travail de thèse. Deux axes essentiels sont développés : l'étude du laser Raman muni d'une fibre standard de télécommunication (laser LSF) et l'étude du laser Raman muni d'une fibre à maintien de polarisation (laser LPMF). Les expériences ont montré que la dynamique du LSF est très riche. En effet la puissance de sortie du signal Stokes est instable et ces instabilités dépendent de la polarisation des différentes ondes se propageant dans la cavité du laser. Le laser PMF quant à lui a un comportement différent : quelque soit l'état de polarisation de l'onde pompe incidente, le signal Stokes en sortie est stable. De plus, nous avons mené une étude résolue en polarisation du laser PMF, mettant en évidence le fait que le laser PMF est constitué de deux lasers indépendants linéairement polarisés le long des axes de biréfringence de la fibre. Ce travail de thèse a également consisté en la modélisation théorique du LSF ainsi que du PMF. Les résultats obtenus sont qualitativement très proches des résultats expérimentaux. Pour cela nous avons inclus dans notre modélisation les effets liés à la polarisation tels que l'effet Kerr et la biréfringence des fibres utilisées.
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Dixon, Nicholas Michael. "Raman microscopy of laser damaged dielectric films and optical fibre inclusions". Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277399.
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Paipetis, Alkiviadis. "A study of carbon fibre/epoxy interface using remote laser Raman microscopy". Thesis, Queen Mary, University of London, 1997. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25538.
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The micromechanics of reinforcement of model carbon fibre/epoxy composites has been investigated using the technique of Remote Laser Raman Microscopy. The technique allows in situ axial stress monitoring in highly crystalline fibres, such as carbon. For this purpose a remote fibre -optic probe was designed and tested. Tailor - made optics have been introduced at both input and output positions of each fibre - optic to provide laser collimation and maximum efficiency. The probe design takes advantage of the pinhole nature of the optical fibre to achieve depth discrimination. A full characterisation of the high modulusM 40 fibres using conventional testing and Raman Spectroscopy preceded the study of the stress transfer. The study was performed as a function of fibre sizing, coupon geometry and elevated temperature. Model composites were subjected to incremental tensile loading, while the stress in the fibre was monitored at each level of applied strain. The stress transfer regime was studied in the elastic domain using the short fibre coupon test and shear lag approach was employed to model the stress transfer efficiency of the interface through the use of the shear-lag parameter/ The study of the long fibre coupon test led to the identification of interfacial failure mechanisms which were also investigated by Scanning Electron Microscopy (SEM). Finally, the stress build-up in the fibre in the presence of energy dissipation mechanisms was modelled,and the stress-transfer efficiency was assessed at different levels of applied composite strain.
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Rosa, Paweł. "Quasi-lossless data transmission with ultra-long Raman fibre laser based amplification". Thesis, Aston University, 2014. http://publications.aston.ac.uk/22442/.
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The project consists of an experimental and numerical modelling study of the applications of ultra-long Raman fibre laser (URFL) based amplification techniques for high-speed multi-wavelength optical communications systems. The research is focused in telecommunications C-band 40 Gb/s transmission data rates with direct and coherent detection. The optical transmission performance of URFL based systems in terms of optical noise, gain bandwidth and gain flatness for different system configurations is evaluated. Systems with different overall span lengths, transmission fibre types and data modulation formats are investigated. Performance is compared with conventional Erbium doped fibre amplifier based system to evaluate system configurations where URFL based amplification provide performance or commercial advantages.
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Dupee, James David. "On-line crystallinity and temperature measurements of nylon 6,6 using a remote laser Raman probe". Thesis, Queen Mary, University of London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287935.
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Fortin, Vincent. "Développement de lasers à fibre basés sur la conversion Raman émettant entre 2 et 4 um". Doctoral thesis, Université Laval, 2014. http://hdl.handle.net/20.500.11794/25368.
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Les lasers à fibre sont des sources robustes, efficaces et qui présentent une qualité de faisceau irréprochable. Cependant, la plupart sont généralement limités à certaines bandes spectrales bien définies, coïncidant avec les transitions électroniques des ions de terres rares. Les cavités laser basées sur la conversion Raman sont une alternative intéressante qui permet de générer, avec une combinaison de pompe et de fibre adéquate, un rayonnement laser à n’importe quelle longueur d’onde. Ces sources permettraient notamment de couvrir la plage spectrale entre 2 et 4 m, convoitée pour diverses applications dans le domaine médical, spectroscopique et militaire. Or, les fibres de silice standards, dont l’atténuation croît rapidement aux longueurs d’onde dépassant 2.2 m, ne sont pas adaptées pour cette application. Bien que les fibres de la famille des verres fluorés ou des chalcogénures présentent plusieurs défis techniques, elles répondent beaucoup mieux aux exigences requises. Dans le cadre de notre projet, nous avons fait l’étude de sources laser basées sur la conversion Raman dans une fibre en fluorozirconate et dans une fibre en sulfure d’arsenic (As2S3). Il s’agissait des toutes premières démonstrations expérimentales de cavités Raman dans ces matériaux. Nous avons également développé des programmes de simulation numérique afin d’en faire l’optimisation et d’identifier leurs limites. En premier lieu, des cavités Raman en fluorozirconate émettant autour de 2.2 m et pompées par un laser Tm:silice à 2 m ont été assemblées et perfectionnées. En imbriquant les cavités Raman et de la pompe, de hautes puissances atteignant quelques watts ont pu être mesurées à la sortie. En second lieu, nous avons fait la démonstration de cavités Raman en As2S3 émettant dans l’infrarouge moyen, à 3.34 m. Elles étaient pompées par une source laser Er3+:ZBLAN à 3 m que nous avons également développée dans nos laboratoires. En raison du gain Raman élevé des chalcogénures, nous avons pu monter ces cavités à partir de quelques mètres de fibre seulement. Les résultats obtenus au cours de notre projet sont probants et font des lasers à fibre une option viable pour l’émission de radiations cohérentes à des longueurs d’onde comprises entre 2 et 4 um.Fiber lasers are robust, reliable and efficient laser sources that also offer an unrivaled beam quality, but most are limited to the specific spectral bands where rare-earth electronic transitions exist. Raman fiber lasers, however, can be operated on virtually any emission wavelength and can be used to bridge the gap between these rare-earth emission bands. Therefore, they could be designed to emit on any wavelength between 2 and 4 m, which would find many applications in the medical, military and spectroscopic fields. Standard silicate fibers cannot be considered for this purpose, due to their limited transparency at wavelengths over 2.2 m. Fluoride and chalcogenide glass fibers are much better suited for this task even though they bring new technical challenges. During our Ph.D. project, Raman lasers based on both fluorozirconate and arsenic trisulphide (As2S3) glass fibers were studied. In fact, we reported the very first experimental Raman cavities based on these materials. First, fluorozirconate Raman cavities emitting around 2.2 m and pumped by a Tm:silica fiber laser were assembled and perfected. Based on an architecture where the Raman and pump laser cavities are nested, we have achieved high output power levels, up to a few watts. We have also demonstrated As2S3 Raman cavities operating directly in the mid-infrared, at 3.34 m. They were pumped by an in-house made erbium doped fluoride fiber laser at 3 m. Due to the high Raman gain of chalcogenide glasses, only a few meters of fiber were required. The behavior of these laser sources was also investigated numerically to find their optimal operating parameters and to identify their limits. The results obtained prove that fiber lasers are well suited for generating a wide range of wavelengths between 2 and 4 um.
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Huneault, Mathieu. "Investigation numérique de l'instabilité Raman dans les lasers à fibre optique dopée à l'ytterbium en régime continu de haute puissance". Master's thesis, Université Laval, 2019. http://hdl.handle.net/20.500.11794/34745.
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Les lasers à fibre optique dopée à l’ytterbium en régime continu de haute puissance ontune part de marché grandissante pour des applications d’usinage de métaux. Malgré qu’il s’agisse d’une technologie relativement répandue, un important problème subsiste dans laplupart de ces lasers. À haute puissance, la diffusion Raman stimulée transfère une partie de la puissance de la longueur d’onde principale d’émission des lasers autour de 1070 nm à la première bande de Stokes Raman autour de 1120 nm, ce qu’on appelle l’instabilité Raman. Cette puissance transférée est inutilisable et peut même être dangereuse pour le système laser et ses utilisateurs. Malgré les travaux théoriques et expérimentaux effectués sur ces lasers, très peu d’explications ont été fournies sur les liens entre les paramètres de la fibre optique et des réseaux de Bragg formant la cavité laser et l’instabilité Raman. Le but du projet de maîtrise présenté dans ce mémoire est donc de développer un modèle de simulation numérique de ces lasers, afin de comprendre et d’identifier les mécanismes dominants qui favorisent l’instabilité Raman et de trouver des configurations de montage la minimisant. Ce mémoire présente les deux modèles de simulation développés dans le cadre de ce projet. Le premier traite la propagation du signal laser comme étant unidirectionnelle, alors que le second la traite comme étant bidirectionnelle, ce qui se rapproche plus de la situation expérimentale. Le montage typique simulé est constitué d’une fibre optique à double gaine dopée à l’ytterbium ayant une grande aire modale effective, d’un réseau de Bragg à haute réflectivité et d’un réseau de Bragg à faible réflectivité servant de coupleur de sortie. Les simulations ont permis d’identifier cinq paramètres de la cavité laser ayant un impact important sur l’instabilité Raman. Une faible puissance moyenne du signal, une courte fibre optique de gain, une configuration de pompage en contrapropagation, c’est-à-dire par le côté du coupleur de sortie, ainsi qu’une plus faible réflectivité et une large bande réfléchissante du réseau de Bragg à faible réflectivité permettent de limiter la génération de l’instabilité Raman. L’optimisation de ces paramètres permet d’obtenir une cavité laser ayant extrêmement peu d’instabilité Ra-man. Ce faible niveau d’instabilité Raman semble être causé par une plus faible puissance intracavité, une courte distance de propagation et des modulations rapides de la puissance du signal. Des montages simulés incluant un filtre dans la cavité à la longueur d’onde de Stokes Raman, un réflecteur non linéaire ou une cavité de basse puissance amplifiée ont également montré une réduction significative de l’intensité de l’onde de Stokes Raman.Continuous high-power ytterbium-doped fiber lasers have an increasing market share formetal processing applications. Despite their widespread use, these lasers still suffer a ma-jor problem. At high power, stimulated Raman scattering shifts the power from the main emission wavelength around 1070 nm to the first Raman Stokes sideband around 1120 nm. This process is called Raman instability. The shifted power becomes useless and can even be dangerous for both the laser system and its users. Previous experimental and theoretical analyses have failed to provide clear explanations on the link between the Raman instability and the parameters of the ytterbium-doped optical fiber and the fiber Bragg gratings forming the laser cavity. The goal of this master’s degree project was to develop a simulation model for continuous high-power ytterbium-doped fiber lasers in order to identify and understand how the parameters of the laser cavity affect the Raman instability and to find cavity configurations that reduce it. This master’s thesis presents the two simulation models developed during this project. The first model considers unidirectionnal propagation of the laser signal while the second one considers bidirectionnal propagation. The latter is thus a more realistic model of such lasers.The typical simulated setup is made of a double-clad ytterbium-doped fiber with a large mode area, a high reflectivity Bragg grating and a low reflectivity Bragg grating that isused as output coupler. The simulations allowed to identify five cavity parameters having an impact on the Raman instability. A low average power, a short gain fiber, a counter-propagation pumping setup as well as a low reflectivity and a large reflective bandwidth for the fiber Bragg grating used as the output coupler help minimizing the Raman instability.The optimisation of these parameters creates a laser cavity with an extremely low power shift to the Raman Stokes sideband. The low Raman instability seems to be caused by a lower intra-cavity power, a shorter propagation distance and fast power modulations in thesignal. Incorporating a filter in the cavity, using a nonlinear reflector as output coupler or using a setup that includes a low-power master oscillator in combination with a high-power amplifier have also been simulated and show a reduction of the Raman instability.
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Ziemieńczuk, Marta [Verfasser], i Philip [Akademischer Betreuer] Russell. "Coherent Gas-Laser Interactions via Stimulated Raman Scattering in Hollow-Core Photonic Crystal Fibers / Marta Ziemieńczuk. Betreuer: Philip Russell". Erlangen : Universitätsbibliothek der Universität Erlangen-Nürnberg, 2012. http://d-nb.info/1023597489/34.
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Abdolghader, Pedram. "Coherent Nonlinear Raman Microscopy and the Applications of Deep Learning & Pattern Recognition Methods to the Extraction of Quantitative Information". Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42677.
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Coherent Raman microscopy (CRM) is a powerful nonlinear optical imaging technique based on contrast via Raman active molecular vibrations. CRM has been used in domains ranging from biology to medicine to geology in order to provide quick, sensitive, chemical-specific, and label-free 3D sectioning of samples. The Raman contrast is usually obtained by combining two ultrashort pulse input beams, known as Pump and Stokes, whose frequency difference is adjusted to the Raman vibrational frequency of interest. CRM can be used in conjunction with other imaging modalities such as second harmonic generation, fluorescence, and third harmonic generation microscopy, resulting in a multimodal imaging technique that can capture a massive amount of data. Two fundamental elements are crucial in CRM. First, a laser source which is broadband, stable, rapidly tunable, and low in noise. Second, a strategy for image analysis that can handle denoising and material classification issues in the relatively large datasets obtained by CRM techniques. Stimulated Raman Scattering (SRS) microscopy is a subset of CRM techniques, and this thesis is devoted entirely to it.
Although Raman imaging based on a single vibrational resonance can be useful, non-resonant background signals and overlapping bands in SRS can impair contrast and chemical specificity. Tuning over the Raman spectrum is therefore crucial for target identification, which necessitates the use of a broadband and easily tunable laser source. Although supercontinuum generation in a nonlinear fibre could provide extended tunability, it is typically not viable for some CRM techniques, specifically in SRS microscopy. Signal acquisition schemes in SRS microscopy are focused primarily on detecting a tiny modulation transfer between the Pump and Stokes input laser beams. As a result, very low noise source is required. The primary and most important component in hyperspectral SRS microscopy is a low-noise broadband laser source.
The second problem in SRS microscopy is poor signal-to-noise (SNR) ratios in some situations, which can be caused by low target-molecule concentrations in the sample and/or scattering losses in deep-tissue imaging, as examples. Furthermore, in some SRS imaging applications (e.g., in vivo), fast imaging, low input laser power or short integration time is required to prevent sample photodamage, typically resulting in low contrast (low SNR) images. Low SNR images also typically suffer from poorly resolved spectral features. Various de-noising techniques have been used to date in image improvement. However, to enable averaging, these often require either previous knowledge of the noise source or numerous images of the same field of view (under better observing conditions), which may result in the image having lower spatial-spectral resolution. Sample segmentation or converting a 2D hyperspectral image to a chemical concentration map, is also a critical issue in SRS microscopy. Raman vibrational bands in heterogeneous samples are likely to overlap, necessitating the use of chemometrics to separate and segment them.
We will address the aforementioned issues in SRS microscopy in this thesis. To begin, we demonstrate that a supercontinuum light source based on all normal dispersion (ANDi) fibres generates a stable broadband output with very low incremental source noise. The ANDi fibre output's noise power spectral density was evaluated, and its applicability in hyperspectral SRS microscopy applications was shown. This demonstrates the potential of ANDi fibre sources for broadband SRS imaging as well as their ease of implementation. Second, we demonstrate a deep learning neural net model and unsupervised machine-learning algorithm for rapid and automated de-noising and segmentation of SRS images based on a ten-layer convolutional autoencoder: UHRED (Unsupervised Hyperspectral Resolution Enhancement and De-noising). UHRED is trained in an unsupervised manner using only a single (“one-shot”) hyperspectral image, with no requirements for training on high quality (ground truth) labelled data sets or images.
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Ayoub, Anas. "Sources laser ultrarapides performantes dans le moyen IR et le Tz". Thesis, Normandie, 2020. http://www.theses.fr/2020NORMR044.
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La sonde atomique tomographique est un instrument d’analyse de la matière à trois dimensions avec une résolution atomique. Cet instrument s’appuie sur l’effet de champ électrique généré à l’extrémité d’un échantillon taillé sous la forme d’une aiguille nanométrique pour faire évaporer les atomes de surface qui sont collectés par un détecteur à deux dimensions. La mesure du temps de vol des ions dont l’évaporation est déclenchée par une impulsion électrique ou optique permettent de remonter à la composition chimique en plus de la localisation 3D des atomes. Dans les sondes atomiques actuelles, l’évaporation atomique est déclenchée par un laser ultrarapide émettant dans l’UV. Cependant, l’interaction de la lumière UV avec la matière induit un échauffement thermique qui limite la résolution en masse de l’instrument et empêche son exploitation pour l’analyse de matériaux fragiles comme les composants biocompatibles. Ces travaux de thèse visent à étudier des solutions pour favoriser l’évaporation rapide tout en inhibant les effets thermiques indésirables dans le cadre d’une sonde atomique laser. Notre approche consiste à exploiter des impulsions ultracourtes dans le domaine du moyen infrarouge ou du THz en raison de leur grande énergie pondéromotrice associée à une faible énergie de photon. Ce manuscrit rapporte sur le développementd’un banc de génération et caractérisation d’impulsions THz intenses. Le couplage de ces rayonnements avec une nano-pointe métallique polarisée négativement a permis de caractériser le champ proche induit à la surface de la nano-pointe qui est fortement modifié par l’effet d’antenne de cette dernière. La deuxième partie rapporte sur le développement d’une source laser ultrarapide de haute cadence accordable dans le moyen infrarouge autour de 3 mm en exploitant des fibres en verre fluoréThe atome probe tomography is an instrument for analyzing matter in three dimensions with atomic resolution. This instrument relies on the effect of an electric field generated at the end of a sample cut into the shape of a nanoscale needle to evaporate the surface atoms which are collected by a two-dimensional detector. The measurement of the time of flight of the ions whose evaporation is triggered by an electrical or optical pulse makes it possible to measure the chemical composition in addition to the 3D localization of the atoms. In current atome probes, atomic evaporation is triggered by a high-speed laser emitting in the UV. However, the interaction of UV light with matter induces thermal heating which limits the mass resolution of the instrument and prevents its use for the analysis of fragile materials such as biocompatible components. This thesis work aims to study solutions to promote rapid evaporation while inhibiting unwanted thermal effects of the laser in atome probe. Our approach consists in exploiting ultrashort pulses in the mid-infrared or THz domain due to their high ponderomotive energy associated with low photon energy. This manuscript reports on the development of a bench for the generation and characterization of intense THz pulses. Coupling these radiations with a negatively polarized metallic nanotip has made it possible to characterize the near field induced at the surface of the nanotip, which is strongly modified by the antenna effect. The second part reports on the development of an ultra-fast laser source tunable in the mid-infrared around 3 mm using fluoride glass fibers
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Carrier, Julien. "Écriture de réseaux de Bragg par laser femtoseconde à 400 NM". Thesis, Université Laval, 2013. http://www.theses.ulaval.ca/2013/29736/29736.pdf.
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Les réseaux de Bragg occupent une place importante dans le secteur des composants optiques fibrés. En effet, ils permettent de filtrer et contrôler la lumière qui voyage à travers les réseaux de télécommunication. Ils réalisent cette tâche en réfléchissant une partie du signal autour d’une longueur d’onde appelée longueur d’onde de Bragg. Traditionnellement, leur fabrication se fait par irradiation d’une fibre de silice à un faisceau laser UV. Dans ce cas, l’écriture est limitée à la silice en raison des mécanismes de photosensibilité propre à la matrice de ce verre et qui sont malheureusment nécessaires à l’inscription des réseaux. Dans certains cas, ceci peut être problématique. En effet, pour le développement de sources lasers tout-fibres, une application technologique d’importance, il est d’usage que la cavité soit basée sur une fibre à composition exotique qui ne possèdent pas nécessairement les mêmes mécanismes de photosensibilité que la silice. Le développement récent de sources lasers ultrarapides et ultraintenses présente une solution à ce problème. En effet, en utilisant des impulsions femtosecondes, il est maintenant possible de prendre avantage d’une multitude d’effets non linéaires, qui eux sont universels, afin de générer la photosensibilité souhaitée. À ce jour, la plupart des travaux se sont réalisés grâce à des impulsions de 800 nmen longueur d’onde. Or, il s’avère qu’utiliser une longueur d’onde plus courte comporte certains avantages. Premièrement, ceci permet l’accès à des longueurs d’onde Bragg plus faibles. Ceci pourrait être utile dans le développement de sources lasers émettant dans le visible. Par ailleurs, des impulsions à plus haute énergie génèrent davantage d’effets nonlinéaires ce qui, théoriquement, se traduit pas une plus grande photosensibilité du milieu. Pour ces raisons, une longueur d’onde d’inscription de 400 nm a été choisie pour la réalisation de ces travaux. Par ailleurs, la technique d’écriture par balayage d’un masque de phase a été utilisée pour fabriquer les réseaux. Cette technique, qui n’avait jamais encore été étudiée pour l’écriture femtoseconde à 400 nm, est basée sur l’interférence des deux premiers ordres de diffraction d’un masque de phase. De plus, il est possible de balayer la fibre de façon longitudinale et transversale grâce à une platine de translation et un actuateur piézoélectrique de manière à maximiser la réflectivité du réseau et contrôler ses caractéristiques spectrales. Grâce à ce montage, l’écriture à 1 µm dans une fibre de silice a été optimisée. Dans les conditions de focalisation de notre expérience, il faut, pour d’obtenir un taux d’écriture maximal, que la distance fibre-masque soit entre 1,7 nm et 3 mm, que l’énergie des impulsions soit entre 250 et 400 µJ et que la vitesse de déplacement de la platine soit la plus faible possible (v = 1 mm/min est généralement utilisée). Par ailleurs, nous avons montré que le recuit thermique de réseaux inscrits dans de la fibre de silice non photosensibilisée, hydrogénée et deutérisée résorbent leurs pertes sans pour autant sacrifier leurs performances. Le profil des filaments a également été caractérisé grâce à des mesures de réfractométrie en champ proche. Sans balayage transversal, nous avons constaté que les filaments traversant la fibre était en régime unique. Dans le cas avec balayage à une fréquence de 20 Hz, nous avons montré que la zone de changement d’indice, bien qu’étendue, était non uniforme. Des simulations numériques et des mesures de tensions aux bornes de l’actuateur piézoélectrique, nous a montré que pour assurer l’uniformité, il fallait respecter un rapport fréquence piézoélectrique sur vitesse de déplacement de la platine ne dépassant pas 0,01 avec une fréquence piézoélectrique ne dépassant pas 1 Hz. Finalement, l’uniformité est aussi affecter par l’amplitude de balayage transversale par rapport au rayon de la fibre en raison de l’effet de la courbure de la fibre. Pour éviter une déformation trop importante, il est de mise que ce rapport soit en deçà de 0,1. Un autre aspect des travaux à porter sur l’écriture de réseaux à pas courts pour le visible. En utilisant un masque de phase uniforme de pas Λ = 655 nm, il a été possible d’inscrire un réseau de deuxième ordre à 480 nm. Les pertes importantes causées par la présence de nombreuses bandes d’absorption associées aux centres de couleurs ont été résorbées à un niveau de 8,8 %. Finalement, des contributions aux projets respectifs de mes collègues Vincent Fortin et Jérôme Leclerc-Perron soit le développement d’un laser Raman dans le verre fluoré et celui d’un laser pulsé tout-fibre pour l’infrarouge ont été faites en inscrivant des réseaux pour leur cavité laser.
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Doutre, Florent. "Sources d'impulsions brèves basées sur des procédés de découpe non linéaires au sein d'une fibre optique ; nouvelles sources déclenchées à cavités couplées". Phd thesis, Université de Limoges, 2010. http://tel.archives-ouvertes.fr/tel-00682880.
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Cette thèse traite de l'amélioration de certaines caractéristiques des impulsions lumineuses émises par un microlaser. D'une part, on exploite le fait que ces impulsions injectées dans une fibre optique subissent une rotation non linéaire de leur polarisation et une diffusion Raman. Un double filtrage spectral et en polarisation permet de pratiquer une découpe temporelle permettant un raccourcissement ajustable de leur durée jusqu'à un facteur 16 (de 600ps à 32ps). D'autre part, une source à double cavité imbriquée incluant un microlaser est déclenchée par un procédé hybride actif/passif. Cette configuration originale présente une gigue temporelle inférieure de deux ordres de grandeur à celle d'un microlaser passif seul. Ces techniques permettent l'émission d'impulsions brèves, stables, avec une gigue réduite à partir de sources miniatures peu coûteuses, particulièrement attrayantes pour des applications de télédétection comme la cytométrie en flux, le LIDAR ou la spectroscopie CARS.
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Steinberg, David. "Laser Raman à fibra operando na banda O em regime de acoplamento passivo de modos utilizando nanotubos de carbono como absorvedores saturáveis". Universidade Presbiteriana Mackenzie, 2015. http://tede.mackenzie.br/jspui/handle/tede/1531.
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Previous issue date: 2015-08-27Fundo Mackenzie de Pesquisa
In this thesis, for the first time we present results of passively-mode-locking O-band Raman fiber laser operating at 1310 nm by using carbon nanotubes as saturable absorber. The first results were obtained for an experimental setup based on single mode fiber (SMF) with laser operating near zero fiber dispersion at 1310 nm at anomalous regime. In this same configuration, a study of pulse duration shortening in terms of intracavity dispersion management with dispersion shifted fiber lengths (DSF) was performed. Replacing the SMF by a highly doped germanium fiber as gain medium of Raman fiber laser, operation was shifted to normal dispersion regime and passive mode-locking was also generated. In this laser, a study of pulse duration shortening in terms of gain medium length reduction was performed and the picosecond pulse regime of the laser could be estimated. We also present a brief comparison between the two dispersion regimes of the Raman fiber laser and passive mode-locking results obtained with different diameters of carbon nanotubes as saturable absorbers.
Nesta tese, apresentamos pela primeira vez resultados do acoplamento passivo de modos em um laser Raman à fibra operando em 1310 nm na banda O, utilizando nanotubos de carbono como absorvedor saturável. Os primeiros resultados foram obtidos de uma configuração experimental baseada totalmente em fibra monomodo padrão (SMF) com o laser operando próximo ao zero de dispersão da fibra em 1310 nm, porém em regime anômalo. Nesta mesma configuração, um estudo do encurtamento da duração do pulso em função do gerenciamento da dispersão intracavidade com comprimentos de fibra de dispersão deslocada (DSF) foi realizado. Substituindo a SMF por uma fibra altamente dopada com germânio como meio do ganho do laser Raman, a operação do laser foi deslocada para o regime de dispersão normal e o regime de acoplamento passivo de modos também foi gerado. Neste laser, um estudo do encurtamento da duração do pulso em função da redução do comprimento do meio de ganho foi realizado e a operação do acoplamento passivo de modos do laser em regime de picossegundos pôde ser estimada. Também apresentamos uma breve comparação entre os dois regimes de dispersão do laser Raman à fibra e resultados do acoplamento passivo de modos obtidos com diferentes diâmetros de nanotubos de carbono como absorvedores saturáveis.
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Olmedo, Herrero Elena. "Étude des effets non linéaires dans les lasers et amplificateurs de puissance à fibre double gaine dopée Er3+/Yb3+". Phd thesis, Télécom ParisTech, 2003. http://pastel.archives-ouvertes.fr/pastel-00000743.
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Depuis quelques années, nous assistons à une augmentation soutenue de la demande en puissance des sources optiques. L'introduction des fibres à double gaine dopées Er3+/Yb3+ dans la conception des lasers et des amplificateurs a permis l'obtention de puissances très élevées, impossibles à imaginer quelques années auparavant. L'évolution de cette technologie, conçue en principe pour des systèmes télécom, permet d'envisager de nombreuses applications dans d'autres secteurs tels que le médical, la découpe laser, le marquage, le lidar, le perçage, le soudage, ou le traitement de surface, entre autres. Du fait des fortes puissances mises en jeu dans de tels composants, l'apparition des effets non linéaires devient incontournable. Les effets non linéaires sont à l'origine d'interférences ou de distorsions qui dégradent considérablement les signaux. La compréhension de ces effets devient donc indispensable dans l'optique de trouver des règles d'ingénierie aidant à les minimiser lors de la conception de nouveaux composants. Ce mémoire présente une contribution, à la fois théorique et expérimentale, à l'étude des effets non linéaires dans les lasers et amplificateurs de puissance à fibre double gaine dopée Er3+/Yb3+, portant plus particulièrement sur l'automodulation de phase et la diffusion Brillouin stimulée. L'automodulation de phase a été traitée dans le cas des impulsions d'une durée inférieure à 4 ps. Après une mise en évidence expérimentale, un outil de simulation a été créé à l'aide de l'équation de Schrödinger non linéaire avec gain. Afin d'obtenir des impulsions de puissance supérieure à celle imposée par l'automodulation de phase, un système d'amplification d'impulsions utilisant l'architecture CPA ('Chirped Pulse Amplification') a été mis en place, permettant l'obtention d'impulsions de 450 fs avec une puissance crête supérieure à 35 kW. Dans le cas des impulsions larges -d'une durée supérieure à 10 ns-, la puissance maximum de sortie est limitée par un autre effet: la diffusion Brillouin stimulée. Cet effet a également été mis en évidence de façon expérimentale, puis modélisé à l'aide d'un système de cinq équations couplées. Comme dans le cas de l'automodulation de phase, un outil de simulation a aussi été créé. D'autres effets, tels que la diffusion Raman stimulée ou l'amplification paramétrique ont également été étudiés de façon expérimentale.
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Goutaland, François. "Processus multiphotoniques, défauts ponctuels et mécanismes de leur formation dans les fibres optiques : étude par spectroscopie laser". Saint-Etienne, 1998. http://www.theses.fr/1998STET4021.
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Ce mémoire se compose de deux parties, la première consacrée à l'étude des processus multiphotoniques se produisant dans des fibres optiques fortement dopées avec des ions er3+ et yb3+, et la seconde à l'étude des défauts induits par différents traitements dans des fibres germanosilicates. En étudiant la spectroscopie d'émission des fibres fortement dopées, sous excitations visibles (488 nm) et infrarouge (790 - 880 nm), nous mettons en évidence les différents mécanismes aux émissions bleues, vertes et rouge observées. Deux principaux types de processus d'up - conversion peuvent alors être distingués : ceux faisant appel aux transferts d'énergie Yb er et ceux faisant intervenir le phénomène d'absorption dans l'état excité (ESA). L'influence de la longueur de fibre et des concentrations en ions de terre rare sur les efficacités respectives de chacun de ces deux mécanismes est ensuite abordée. Après une présentation bibliographique des différents défauts dans la silice et les fibres germanosilicates, nous présentons le phénomène appelé dépendance modale du spectre d'émission d'une fibre optique, c'est-à-dire la variation du spectre d'émission d'une fibre en fonction du mode excité. L'évolution avec la température d'une bande d'émission centrée autour de 600 nm nous permet ensuite d'attribuer cette émission à des radicaux péroxys. Nous montrons alors que ces radicaux péroxys peuvent être photoinduits dans le CUR des fibres par irradiation intense à 488 nm. Enfin, nous étudions par spectroscopie Raman et spectroscopie d'émission les défauts générés dans deux types de fibres germanosilicates irradiées à 240 nm. Une technique de filtrage spatial du mode excité permet alors de séparer les défauts photoinduits dans le CUR de ces fibres de ceux localisés près de l'interface CUR/gaine
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Aparanji, Santosh. "Power Combining of Raman Fiber Lasers". Thesis, 2020. https://etd.iisc.ac.in/handle/2005/5111.
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Fiber lasers have become ubiquitous in industry and research for their numerous attractive properties that other lasers such as solid state lasers lack. However, conventional doped fiber lasers, though providing high power, do so only at specific wavelengths, with lots of white spaces in the spectrum. Raman Fiber Lasers are currently the only known mature technology to achieve wide degree of wavelength agility with high powers. Such Raman fiber lasers start off with a single high power pump source at a given wavelength and use the concept of Stimulated Raman Scattering to get to the otherwise inaccessible longer wavelengths through a series of Stokes shifts. Using a single pump has its own drawbacks, as it would primarily overburden the single high power pump source (and also leads to Raman instability). This thesis starts with mitigating these drawbacks to power scaling of Raman lasers by proposing the concept of nonlinear Raman based power combining.
The goal of Raman based power combining is to see if one can achieve simultaneous power combining and wavelength conversion of multiple lower power laser modules into a single lasing line at any arbitrarily longer wavelength through the Raman effect. By using multiple lower power modules, one would not stress the system components and failure of one of the components would not lead to a total collapse of the system. A greater bonus would be if all these pump modules were operating at different wavelengths (but in the same band) and yet if one could achieve a wavelength conversion to a single lasing line (with a combined power of the input modules). This is what has been demonstrated in this work, where the first step was to perform a simultaneous power combining of two ~ 100 W class lasers operating at different wavelengths in the Yb emission band (1 μm band) to a single lasing line of ~ 100 W at the 1.5 micron band. An explanation is proposed for why the nonlinear power combining technique works the way it does, viz., why it leads to a single lasing line rather than a dual wavelength output.
The next step is to see the limits of power combining. Does the proposed method work for any arbitrarily spaced wavelength pumps? How close do the pump lasers have to be before the technique works no more? How far apart can they be? Specifically, it is shown that the technique of nonlinear Raman based power combining works even in the impressive scenario where the pumps are separated by as close as 5 nm (for pump input wavelengths of 1074 nm and 1079 nm). And it works when they are separated as large as 29 nm, which is almost half a Stokes shift away (for pump input wavelengths of 1088 nm and 1117 nm). This proves the versatility of the technique for two pumps. The versatility of the nonlinear power combining technique is further strengthened by demonstrating the technique with 3 input pump lasers all operating at different wavelengths (pump wavelengths of 1074 nm, 1088 nm and 1117 nm). Even in this scenario, simultaneous power combining and wavelength conversion to a single lasing line in the 1.5 micron band is demonstrated, with more than 90% of the power residing in the final band!
A serendipitous discovery in the process of achieving Raman based power combining was to observe the Raman fiber spools glowing an iridescent rainbow of hues – all this when the input pump lasers and the Stokes wavelengths were in the Near Infrared (NIR). This led to the fascinating study and understanding of visible light generation in Raman fibers. Specifically in this thesis, it is theorised that the visible rainbow of hues is formed due to the harmonic conversion of the propagating NIR Stokes in the Raman fiber and mediated through a Cherenkov phase matching process which enables the light to escape from the cladding of the fiber. What follows is an extremely rigorous mathematical analysis of the entire phenomenon. The fruit of such rigor led to the development of a robust image processing algorithm that takes as input static DSLR images of the glowing Raman fiber spools and produces as the output a length-resolved plot of the effective NIR Stokes wavelengths propagating in the core of the fiber. This is extremely beneficial as a non-contact diagnostic tool for spectral analysis of fiber lasers. Further verification of the mathematical theory developed is provided where the same theory is applied to analyse the visible light generation in a fiber supercontinuum source developed in-house. The mathematical model was remarkably successful in predicting the visible spectrum which was verified with a visible spectrometer.
In summary, this research thesis aims to advance the field of Raman fiber lasers by delving into more niche yet extremely fruitful aspects, beyond the typical view that they are just a source to achieve wavelength tunability. Innovative power combining approaches and a solid analysis of visible light generation in such Raman fiber lasers, along with an elegant image processing algorithm, all goes to show that with a bit of math, Raman fiber lasers can be the next generation laser systems in every field.MHRD
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Balaswamy, Velpula. "High power Cascaded Raman fiber lasers". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/4731.
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Over the last decade, fiber lasers have gained significant traction for industrial, defense and medical applications. This is owing to their superior beam quality along with power scalability, compactness, reliability and robustness. The current fiber laser technology is based on rare-earth elements such as Ytterbium (Yb), Erbium (Er), Thulium (Tm), Holmium (Ho) etc. which are doped inside the core of an optical fiber which in turn acts as a gain medium. However, current fiber laser technology suffers from serious drawbacks such as limited wavelength coverage and power scalability. Wavelength coverage is limited to the emission spectra of different rare-earth dopants and power scalability is limited to only Yb emission window. For example, tens of Kilo Watts of continuous wave (CW) output power has already been demonstrated at 1μm wavelength region. This a rather serious limitation as there are numerous applications like LIDAR, Free space optical communications etc. which require high power fiber lasers outside the rare-earth emission bandwidths.
Among the several nonlinear frequency conversion techniques for extending the spectral coverage, stimulated Raman scattering (SRS) is proven to be more versatile as it doesn’t require any phase matching conditions to be satisfied. The nonlinear process of SRS converts a shorter wavelength high power pump laser to a long wavelength Stokes laser. This process can be cascaded to longer and longer wavelengths and such systems are called cascaded Raman fiber lasers. Currently, cascaded Raman fiber lasers is the only power scalable technology which offers wavelength diversity while spanning the spectrum.
However, conventional cascaded Raman fiber lasers are limited in terms of efficiency and reliability which stopped them from further power scaling. Even though enhanced efficiency and reliability has been demonstrated, but only at the cost of increased complexity of overall system.
In the 1st part of this thesis, I will be talking on the efforts that I have made in making cascaded Raman fiber lasers highly efficient and reliable with as simple architecture as possible. In this work, a new, all-passive architecture for high-efficiency cascaded Raman conversion is demonstrated. This architecture has been tested out with a fifth-order cascaded Raman converter from 1117nm to 1480nm with output power of ~64W and efficiency of 60%.
Even though the above system demonstrates the wavelength agility of cascaded Raman fiber lasers, the same system can’t be used if the input pump wavelength is changed. This is because of the use of fixed wavelength fiber Bragg grating sets (RIG and ROG) for wavelength conversion. These grating sets decide both output signal wavelength and the input pump wavelength thereby limiting the wavelength flexibility of these systems. However, Raman gain based on stimulated Raman scattering is available at any arbitrary wavelength inside the optical fiber. Therefore, one can always use a tunable-wavelength pump laser and achieve wavelength tunability at any arbitrary wavelength band with these systems. It necessitates to have tunable-wavelength pump fiber laser and wavelength independent (broadband) feedback mechanism. Hence, motived by the wavelength tunability of cascaded Raman fiber lasers, I have built a high power tunable wavelength Yb-doped fiber laser which has additional property of independent tuning of linewidth and output power. Independent tuning of wavelength (from 1050nm to 1100nm), linewidth (from 0.2nm to 1.4nm) and power (up to 130W) has been achieved in continuous-wave Ytterbium-doped fiber laser. This has been achieved with the help of simple architecture based on master oscillator power amplifier (MOPA) configuration. This system addresses the conventional linewidth vs power coupling relation of fiber laser by demonstrating independent tuning of linewidth and wavelength at a constant output power.
The above high-power, tunable wavelength, Yb-doped fiber lasers is the basic building block (pump source) for our advanced cascaded Raman fiber lasers. By utilizing this pump source, a simple architecture for high-power, fixed, and wavelength tunable, grating-free, cascaded Raman conversion between different wavelength bands has been achieved. The architecture is based on the recently proposed random distributed feedback Raman fiber lasers. Here, a module which converts the ytterbium band to the eye-safe 1.5μm region has been implemented. Pump-limited output powers of over 30W in fixed and continuously wavelength tunable configurations have been achieved.
Cascaded Raman fiber lasers requires termination of Raman cascade for power scaling in the desired wavelength band. In the previous system, termination of cascaded Raman conversion at 1.5μm wavelength band thereby achieving high power wavelength tuning over a bandwidth of one Raman Stokes (1440-1520nm) has been achieved. However, because of the use of specialty Raman filter fiber, termination of cascaded Raman conversion at any arbitrary wavelength is not possible. This is important to achieve power scaling at any arbitrary wavelength within the transmission window of optical fiber.
In final part, I demonstrate such a cascaded Raman fiber laser with both ultra-wide wavelength tunability and power scaling. Here, a novel filtered distributed feedback mechanism has been used to terminate the Raman cascade at desired wavelength and hence naturally achieve power scaling. Output powers of up to 28W has been achieved with >400nm tuning from 1118nm-1535nm, bridging the Ytterbium, Erbium emission bands.
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Arun, S. "Continuous-Wave Supercontinuum Generation using Cascaded Raman Fiber Lasers". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/4888.
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This thesis explains architecture and techniques to generate high power, CW
supercontinuum laser sources using standard Silica fibers as the nonlinear medium, pumped
using high power CW Yb doped fiber lasers. Unlike the pulsed supercontinuum sources,
the CW supercontinuum sources offer high average powers leading to spectacular power
spectral densities at the output and can be realized at lower costs, in an all fiber architecture,
which makes the system more compact and favorable towards power scaling.
We have demonstrated a high power, all-fiber, wavelength tunable, fiber laser source that
can operate in the L-band region (1.5-1.6 um), based on 6th order cascaded Raman
amplification scheme, which can generate ~24 W of output power and is widely tunable
from 1560-1590 nm. Using this laser we could pump the HNLF to generate a
supercontinuum of ~700 nm bandwidth to powers as high as 35 W which is nearly double
the output power than what has been previously demonstrated.
To enhance the bandwidth and scale the output power, we have demonstrated a simple but
highly impactful solution which uses the standard telecom fiber as the nonlinear medium.
The supercontinuum generation module we demonstrated, is essentially a high efficiency
cascaded Raman converter, which can take any CW, high power Ytterbium-doped fiber
laser as the input and generate an octave spanning supercontinuum with an average power
of ~34W, spanning over 1000nm (>1 octave) from 880nm to 1900nm at an efficiency of
~44%. The supercontinuum source exhibited excellent spectral and temporal stability for
an extended duration of operation (>1 hour).
The most highlighting result reported in this thesis is the record high output power that has
been demonstrated from a CW supercontinuum so far. Using the recently proposed
nonlinear power combining architecture we could leverage the output power (limited by
available pump power) from the telecom fiber based octave spanning, CW supercontinuum.
This involves nonlinear spectral power combining of outputs from multiple, independent,
Yb lasers operating at different wavelengths as the pump sources, to generate
supercontinuum at an efficiency of ~44% with a spectacular PSD of >3mW/nm from
850nm-1350 nm and an impressive PSD of >100mW/nm from 1350nm-1900nm at an
output power of ~72 W.
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Choudhury, Vishal. "Raman and Brillouin Nonlinearities in High Power Fiber Lasers: Novel Effects and Applications". Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5563.
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High power fiber lasers due to their immense utility in both industry and research divisions, have seen a dramatic level of power scaling in the last two decades. This is due to the superior beam quality, thermal handling and compact nature inherently offered by all-fiber based systems as compared to other forms of laser systems. As of now, the rare earth doped Ytterbium (Yb), Erbium (Er) and Thulium/Holmium (Th-Hm) fiber lasers have shown remarkable levels of power with Yb outperforming the rest by order of magnitude levels. However as the power in the tightly confined fiber modes scale up, fiber nonlinearity sets into action. Nonlinear effects such as self-phase modulation, modulation instability (MI), supercontinuum (SC) generation, etc alters the spectral and temporal properties of lasers. Similarly nonlinear effects based on photon-phonon interactions, i.e. Raman and Brillouin scattering as well as thermal Rayleigh scattering also hinders or enhances the features of a laser depending upon the application. More recently stimulated Raman scattering (SRS) has evolved to be the only known power scalable technology for generating new wavelength bands, otherwise nonexistent in the rare earth platform. Stimulated Brillouin scattering (SBS) and stimulated thermal Rayleigh scattering (STRS) on the other hand, have been the primary bottleneck in power scaling of narrow linewidth high power lasers. This thesis consisting of two main parts dealing with some new applications and novel effects of SRS and SBS. In the first, we exploit the properties of SRS in silica fiber medium to generate highly spectrally flat SC lasers and subsequently explore their utility in different frontiers. In the second, we demonstrate a widely linewidth tunable high power fiber amplifier which generates an SBS limited kW class narrow linewidth fiber laser showing a previously unseen unique visible light generation phenomena.
Raman fiber lasers (RFL) aided by SRS have very recently been established as the only power scalable route to filling in the gaps between Yb, Er and Th emission windows. Similarly spectrally broad lasers, SC lasers too allow a path to spectrally populate these otherwise inaccessible gaps, though not yet known to be power scalable. We identified the shortcomings in bandwidth, conversion efficiency, power scalability and flatness in the existing SC modules and propose utilizing Raman fiber lasers to simultaneously mitigate all of them. Thus we demonstrated a CW RFL with 24 W power (highest at the time of publishing) tunable across the L-band and subsequently generated a 700 nm broad, 35 W SC with ~40% conversion efficiency. The SC had a remarkable flatness of ~5 dB across at least 400 nm which is highest ever reported so far in all fiber and CW format.
Flat SC generation was followed by exploring the spectral and temporal properties of such lasers. Femtosecond pulse shaping technology enables one to generate light sources with user defined amplitude, phase and polarization in the ultrafast regime. However due to power handling limitations of the components, this technology lacks a bridge with the modern high power fiber lasers. We propose and demonstrate a scalable design for a high power Fourier shaper capable of handling 20 W of CW laser power with simultaneously covering over 450 nm bandwidth between 1-1.5 micron band. Our design implements several modifications from conventional designs to conform with the demands of high power fiber laser technology. We believe that the ability to shape high power SC or RFL sources will potentially aid controlled Raman conversion to increase spectral purity and many more applications. Further, in the experiments concerning the temporal properties of SCs, we proposed a new method of characterizing high speed photodetectors in a spectrally resolved manner. This is enabled by the stochastic pulse nature of CW SCs while simultaneously having broad optical bandwidth. Our method also gives an insight to how the RF source spectra of CW SC varies across the optical bandwidth as well as its evolution from a single wavelength laser through SRS, MI regime etc.
In the second part of the thesis, we demonstrate a high power tunable narrow linewidth laser source at 1064 nm. This was achieved by stepwise amplification of a 1064 nm polarization maintained (PM) DBR (Distributed Bragg reflector) laser, externally phase modulated by a power and bandwidth tunable noise source. This resulted in a tunable linewidth, SBS limited at 10 GHz linewidth laser delivering more than 500 W CW power. This laser operating in the NIR (1064 nm), showed some surprising visible light flashes at a fusion splice point when operated in the SBS regime. Subsequent experimental analysis showed that at the onset of SBS, the backward propagating SBS pulses in the core of the fiber also undergo SRS. This generates multiple Stoke orders of 1064 nm and they eventually undergo Cherenkov type phase matching to the second harmonics of the respective Stoke orders in the cladding of the fiber. Thus any part of the laser with the cladding exposed dissipated the visible light. The analysis was also validated by numerical simulations carried out conforming to the fiber parameters. We believe any laser system with high enough power irrespective of the temporal dynamics could possibly trigger this effect.
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Schröder, Jochen 1976. "Raman scattering and four-wave mixing: from fundamentals to fibre lasers". 2009. http://hdl.handle.net/2292/4269.
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Ramanscattering and four-wave mixing are two fundamental nonlinear phenomena present in optical fibres with important implications for applications in fields ranging from modern telecommunications networks to biophotonics. This thesis investigates three situations when these two phenomena interact: Firstly we investigate the interplay of multiple four-wave mixing processes using coherent and incoherent pump waves in the presence of Raman scattering. We experimentally demonstrate that despite the requirements of phase-matching conditions it is possible to observe multiple phasematched and non-phasematched four-wave mixing processes. Furthermore we show that an incoherent light wave provided by amplified spontaneous emission noise can act as an effective pump wave for degenerate four-wave mixing. The main part of the thesis is occupied by the investigation of a mode-locked Raman fibre laser. The use of dissipative four-wave mixing for the passive mode-locking technique in combination with Raman scattering as the gain mechanism offers the possibility of achieving ultra-high repetition rates at very high average output powers. We experimentally demonstrate the mode-locked operation of the laser at 500 GHz and achieve an average output power of almost 1 W. Additionally we examine the key limitation of the laser which is supermode noise caused by mode-locking the laser at very high harmonics of the cavity resonance frequency. In order to gain qualitative insight into the influence of supermode noise on the laser dynamics we create a laser model which takes account of supermode noise. Furthermore we design a scheme to reduce supermode noise using additional subcavities, and evaluate the scheme using a lower repetition rate laser. We show that by including the subcavities into the setup the amount of supermode noise can be reduced by at least a factor 100. Lastly we introduce a novel method to measure the noise fluctuations of continuous wave lasers at timescales prohibiting the use of traditional noise measurement techniques. The noise is measured using a technique which transfers the fast noise from the continuous wave laser to a low repetition rate mode-locked laser which can be measured with traditional methods. We demonstrate that a continuous wave Raman fibre laser exhibits ultrafast, high contrast intensity fluctuations at timescales of tens of Gigahertz. This work has led to three publications and six conference presentations.
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Krause, Michael [Verfasser]. "Efficient Raman amplifiers and lasers in optical fibers and silicon waveguides : new concepts / von Michael Krause". 2007. http://d-nb.info/994801556/34.
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Leung, Ka-Hei, i 梁家熙. "The Study of tunable spacing multi-channel hybrid Raman/EDF fiber laser with Double Pass Mach Zehnder Interferometer". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/39303046451440942215.
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碩士國立東華大學
光電工程研究所
98
In this paper we presented a multi-wavelength fiber laser structure using a MZI (Mach Zehnder Interferometer) to tune the wavelength spacing. The investigation is mainly in the researches of Mach Zehnder Interferometer structure, resonance cavity structure and gain medium. In the design of interference of Mach Zehnder Interferometer, we employed a manual OVDL (Optical Variable Delay Line) to change the phase difference in two optical paths, so the channel spacing of laser would continuously be tuned from 0.2nm to 1.9nm. We not only designed the tunability of Mach Zehnder Interferometer, but also improved the SNR (Single to Noise Ratio) of interference from 9.7dB to 18.8dB in our Double pass Mach Zehnder Interferometer, which led to the SNR of lasing channels can be over 50dB above in the spacing range. In our ring cavity and linear cavity laser experiments, as the ring cavity structure of which the wave was travelling in one direction while the linear cavity structure of which the wave was back and forth to form a standard wave, so the different resonance properties affected the number of lasing channels. For example, the channel spacing 0.2nm of Erbium Doped Fiber Laser which has only 5 channels in the ring cavity structure, whereas the linear cavity structure could generate 9 lasing channels. Therefore, compared between different laser structures, the linear structure multi-wavelength laser could effectively increase the number of channels. Moreover, we employed the different gain mediums with an EDF (Erbium Doped Fiber), a DCF (Dispersion Compensation Fiber) and a hybrid fiber in the laser structure. The hybrid fiber consisted of an erbium doped fiber and a Raman fiber. In the EDF fiber laser which the EDFA consisted of a 5.58m erbium doped fiber. Although the laser has higher gain and higher SNR, it also has serious homogeneous line broadening and strongly mode competition. So it was difficult to reach multi-wavelength and flat output. For example, the laser output only contained 9 lasing channels and ±4.75dB flatness in the spacing 0.2nm. In the Raman gain fiber laser experiment, the number of lasing channels could reach to 33 and ±4.07dB flatness in spacing 0.4nm, which the RFA consisted of a 4.47km dispersion compensation fiber and it belongs to inhomogeneous broadening mechanism. However, it was limited by the pumping power which led to not sufficient Raman gain to support a large portion of channels over the laser threshold, when the channel spacing was 0.2nm. In the Hybrid gain medium, we focused on the suitable pumping wavelength and the pumping power, because we could clearly understand that these would affect the number of lasing channels and the flatness. In the first experiment, the hybrid gain laser which had a few lasing channels and it was even fewer than the Raman laser when it was pumped by 977.3nm and 1465nm. In the end of our experiment, thereby we designed only two pumping wavelengths, which were 977.3nm and 1480nm, to generate more lasing channels and great flatness output effectively. For example, the number of lasing channels could increase up to 60 with operating channel spacing of 0.2nm, the lasing bandwidth was 12.9nm and the flatness was ±4.2dB.
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Chang, I.-Feng, i 張宜豐. "Numerical Study of Maximum Extractable Energy from Multi-mode Pulsed Fiber Laser Amplifier with Considerations of Stimulated Raman Scattering". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/11195779836976584700.
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碩士國立中央大學
物理學系
103
A numerical study of maximum extractable energy from multi-mode pulsed fiber laser amplifier with considerations of stimulated Raman scattering is presented. Based on rate-propagation equations, a one-dimensional convection code is constructed for calculating the maximum extractable energy in fiber laser amplifiers. In order to derive the dispersion relations of fibers, the effective core area, overlapping integral with considerations of radial-dependence distribution of gain medium, and eigenvalue equations with weakly-guide approximation are also solved using the numerical approach. In the thesis, we extended the single-mode model, which is based on rate-propagation equation, to study the maximum extractable energy in fiber laser amplifiers with a large fiber core. Simulation results show that the criterions of seed energy and input seed pulse width to extract maximum energy in fiber laser amplifiers are determined by the nonlinear phenomenon and multimode effects. The numerical model used in the study can be applied to study the nonlinear effects and the spectral broadening in a large-mode-area (LMA) fiber and provide experimental designs of a practical high-power and high-energy pulsed fiber amplifier.
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Chang, Wei-cheng, i 張惟程. "Noise like pulses with broad spectrum bandwidth from a passive mode-locked Yb-doped fiber laser based on stimulated Raman scattering". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8a935d.
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碩士國立臺北科技大學
光電工程系研究所
105
We investigated the soliton dynamics in passive mode-locked Yb-doped fiber lasers (PML-YDFL) based on nonlinear polarization rotation mechanism (NPR). Once laser was mode-locked, the noise-like pulses were produced that revealed double-scale intensity autocorrelation (IAC) trace. After adding a single mode fiber (HI1060) inside laser cavity to elongate cavity length in this fiber laser, the threshold power for Raman scattering can be efficiently reduced to produce a stimulated Raman scattering without an external power amplification system. In this work, the generated mode-locked pulses with the broadest spectrum bandwidth can be produced after insertion of 150 meters single mode fiber (SMF) inside laser cavity. The spectrum evolution as a function of pump power was monitored with an additional 150 m SMF inside cavity. At the pump power of 241 mW, the second order Raman spectrum with peak wavelength at 1135 nm was generated. In addition, we also compared the speckle image of laser operation at CW, NLP and stimulated Raman state. Furthermore, we demonstrate that the speckle image can be further enhanced after connection a 5 meters long multi-mode fiber to excite higher order modes. The lowest contrast less than 0.04 can be produced in operation at stimulated Raman state with extension of spectrum from 1000 to 1160 nm.
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Κοϊμτζόγλου, Χρήστος. "Μελέτη της επίδρασης της κόπωσης στη διεπιφάνεια ίνας/μήτρας σύνθετων υλικών οργανικής μήτρας και της επίδρασης του φαινομένου στους μηχανισμούς μεταφοράς φορτίων σε μικροσκοπικό επίπεδο, με τη μέθοδο laser Raman spectroscopy". Thesis, 2003. http://hdl.handle.net/10889/8758.
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--One of the most important parameters that affect the mechanical response of composites is the quality of the interfacial bond between the matrix and the reinforcing material. Therefore, the aim of the present work is to investigate the effect of fatigue loading on the integrity of the interfacial bond in fibre-reinforced plastics in microscopic level using the laser Raman spectroscopy technique.