Étude et réalisation de sources femtosecondes haute puissance moyenne

Ce travail de thèse concerne l'augmentation de la puissance moyenne produite par les systèmes femtosecondes amplifiés en conservant ou même en améliorant la robustesse et la compacité de ces sources. La première partie de ce travail de thèse a porté sur les chaînes Titane-Saphir produisant des énergies proches du millijoule. Nous avons cherché à réaliser un système à une cadence de 10khz. L'idée de l'utilisation du cristal à des températures cryogéniques pour améliorer ses propriétés thermiques et thermo-optiques nous a obligés à étudier tout particulièrement les modifications qu'induit le refroidissement sur ses propriétés lasers. Le pompage des matériaux dopés ytterbium se fait par des diodes laser continues ce qui permet de facilement étudier l'évolution des performances d'un système amplifié avec la cadence et de réaliser des sources à très haute cadence (supérieure à 100Kh). Nous avons démontré qu'au-dela d'une fréquence critique l'énergie de sortie d'un amplificateur régénératif pompé en continue affiche une évolution multipériodique mais qu'il est possible de stabiliser ce régime en choisissant des temps d'extraction de l'énergie adaptés. L'amélioration de l'évaluation thermique dans les cristaux massifs d'Yb:tungstate a aussi permis la réalisation de deux sources originales produisant des impulsions femtosecondes jusqu'à une cadene de 300Khz pour la première et à une énergie supérieure à 1mj pjour l'autre. Malgré ces progrès, la recherche de nouveaux matériaux dopés ytterbium qui éventuellement pourraient mieux répondre aux besoins exprimés reste essentiel. Nous avons alors enfin étudié les propriétés laser du cristalde Li6Y(BO3)3 dopé ytterbiumBORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Sectional Chirped Volume Bragg Grating Compressors For High-Power Chirped-Pulse Amplification

Chirped Bragg Gratings (CBGs) recorded in photo-thermo-refractive (PTR) glass have been successfully used as ultrashort pulse stretchers and compressors in a variety of solid-state and fiber chirped pulse amplification (CPA) laser systems. Compared to traditional pairs of surface gratings, CBG-based stretchers and compressors offer significant advantage in compactness and robustness. They are insensitive to polarization, require virtually no alignment and can handle high average and peak power. At the current technology stage PTR-glass CBGs can provide up to 30 nm spectral bandwidth and up to 300 ps stretched pulse duration. In this paper we propose a concept of sectional CBGs, where multiple CBGs with different central wavelengths recorded in separate PTR-glass wafers are stacked and phased to form a single grating with effective thickness and bandwidth larger than each section. We present results of initial experiment in which pulses from a femtosecond oscillator centered at 1028 nm are stretched by a 32-mm thick CBG to about 160 ps and recompressed by a monolithic 32-mm CBG with 11 nm bandwidth and by a sectional CBG with two 16-mm thick sections each having ∼ 5 nm bandwidth and offset central wavelengths: 1025.5 and 1031 nm. In both cases, compressed pulse duration of 350-400 fs, ∼ 1.1 × transform-limit was obtained. These results allow CBG-based pulse stretchers and compressors with high stretch ratio and wide bandwidth to be constructed from multiple sections. © 2010 Copyright SPIE - The International Society for Optical Engineering

Broadband Yb:CaF2 regenerative amplifier for millijoule range ultrashort pulse amplification

International audienceWe report on a diode-pumped regenerative amplifier based on Yb:CaF2 material, delivering pulses up to 1.8mJ pulse energy at a repetition rate of 100Hz. The crystal is pumped at the zero line at 978 nm with a 10W continuous wave (CW) fiber coupled laser diode. The pulses have a spectral bandwidth of 16nm centered at 1040 nm, which indicates a good potential for millijoule range sub 100fs pulse duration after compression. It is also a good candidate for seeding higher energy diode-pumped ytterbium lasers

Generation of 150-fs pulses from a diode-pumped Yb:KYW nonlinear regenerative amplifier

International audienceGeneration of sub-150-fs-level pulses has been obtained from an Yb-doped crystal-based regenerative amplifier by applying an innovative amplification scheme. This scheme is based on optimization of the linear and non-linear phase during the amplification process inside the regenerative amplifier cavity. This technique with Yb:KYW allows to achieve pulse durations from diode-pumped Yb-doped regenerative amplifiers that were up to now only accessible with more complex Ti:sapphire amplifiers. With this Yb-doped tungstate crystal used in regenerative amplifiers, 145 fs pulses centered at 1026 nm with a spectral bandwidth of 14 nm at 50 kHz for an average power of 1.6 W have been generated

Sectional chirped volume Bragg grating compressors for high-power chirped-pulse amplification

Chirped Bragg Gratings (CBGs) recorded in photo-thermo-refractive (PTR) glass have been successfully used as ultrashort pulse stretchers and compressors in a variety of solid-state and fiber chirped pulse amplification (CPA) laser systems. Compared to traditional pairs of surface gratings, CBG-based stretchers and compressors offer significant advantage in compactness and robustness. They are insensitive to polarization, require virtually no alignment and can handle high average and peak power. At the current technology stage PTR-glass CBGs can provide up to 30 nm spectral bandwidth and up to 300 ps stretched pulse duration. In this paper we propose a concept of sectional CBGs, where multiple CBGs with different central wavelengths recorded in separate PTR-glass wafers are stacked and phased to form a single grating with effective thickness and bandwidth larger than each section. We present results of initial experiment in which pulses from a femtosecond oscillator centered at 1028 nm are stretched by a 32-mm thick CBG to about 160 ps and recompressed by a monolithic 32-mm CBG with 11 nm bandwidth and by a sectional CBG with two 16-mm thick sections each having ~ 5 nm bandwidth and offset central wavelengths: 1025.5 and 1031 nm. In both cases, compressed pulse duration of 350-400 fs, ~ 1.1 × transform-limit was obtained. These results allow CBG-based pulse stretchers and compressors with high stretch ratio and wide bandwidth to be constructed from multiple sections

Large-area pulse compression gratings with high efficiency and high damage threshold

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Single-stage Yb:YAG booster amplifier producing 2.3 mJ, 520 fs pulses at 10 kHz (Orale)

International audience520fs, 2.3-mJ pulses are demonstrated in a Yb:YAG booster amplifier delivering peak powers up to 4.4GW. To avoid damage and nonlinear-effect issues, passive divided pulse amplification is studied for the first time for bulk-amplifier. Great efforts have been deployed in the development of laser systems delivering femtosecond pulses for industrial and scientific applications. Among all available technologies, fiber lasers came out as one of the best choice due to their capability to deliver short pulse duration (typically 300 to 500 fs) together with high average power within very reliable and robust systems. Nevertheless, one of the main drawbacks remains the limited output energy available for such laser due to the strong confinement of the light. Standard femtosecond fiber lasers can deliver typically up to 10s µJ energy pulses; and lasers based on rod type technology allow to reach up to the mJ level for laboratory systems [1-2] and 200 µJ for industrial systems. We propose here to enhance the energy from fiber sources by implementing a very simple, but optimized, Yb doped YAG booster stage. This booster consists in using a cm-long crystal to have a simple high gain booster together with a rather-modest length to prevent from deleterious nonlinear effects like self-phase modulation and critical self-focusing. Secondly, the use of a simple and passive divided pulse amplification (DPA) setup [3] is also investigated, in order to exceed the energy limitation. We investigate how the DPA permits to overcome the laser threshold limits from 2.9 mJ to 4.1 mJ. This simple and straightforward amplifier geometry allows to deliver, in a nominal and safe regime, ultrashort pulses below 520fs for energy of 3mJ (before compression) 2.3 mJ after. We demonstrated then pulses up to 4.4 GW of peak power. The fiber laser source used is a standard industrial laser-developed by Amplitude Systems-that delivers pulse energy 180µJ up to 100 kHz repetition rate with duration of 350 fs. By limiting output energy below 200µJ, nonlinear effects and damages threshold in the laser are safely avoid. The Yb:YAG booster is implemented between the fiber amplifier and the compresso

Génération d'impulsions de 100 fs dans un amplificateur régénératif a base d'YB:CALGO (poster)

International audienceDes impulsions ultra-courtes d'une durée de 100 fs ont été obtenues dans un amplificateur régénératif utilisant un cristal d'Yb:CALGO. Le rétrécissement spectral par le gain a été minimisé en employant une technique d'amplification non-linéaire utilisant l'effet Kerr

Sub-100-fs Yb:CALGO nonlinear regenerative amplifier

International audienceWe report on the first diode-pumped Yb∶CaGdAlO 4 regenerative amplifier in the sub-100-fs regime. It generates pulses at a central wavelength of 1047 nm with up to 24 μJ energy (after compression) at a repetition rate of 50 kHz. The measured pulse duration is 97 fs, with a spectral bandwidth of 19 nm. We describe in detail how non-linear effects are optimally used to compensate gain narrowing in order to overcome the 100 fs barrier. Many industrial applications, such as athermal microma-chining [1] or eye surgery, require efficient and compact laser systems delivering ultrashort pulse energies of several tens of microjoules. To reach this energy level, femtosecond systems rely on the well-known chirped pulse amplification (CPA) concept in which nonlinear effects are minimized by sufficient temporal stretching prior to amplification. In terms of gain medium, Nd:glass bulk amplifiers have progressively been replaced by ytterbium (Yb)-doped crystalline materials that are more suited to average power scaling. Among Yb-doped materials, Yb:YAG and Yb:tungstates currently hold a dominant position. The combination of satisfying thermal conductivity together with large and broad absorption and emission cross-sections has allowed their dissemination and a new generation of ultrashort industrial amplifiers. On the other hand, the lack of crystalline disorder, responsible for the good thermal properties, also prevents the generation of sub-100-fs pulses due to the restricted available gain bandwidth. Therefore, typical durations from Yb:tungstate amplifiers are in the range of 200–400 fs [2–5] while for Yb:YAG-based amplifiers, the obtained pulse widths are typically between 500 fs and 1 ps [6,7]. Several Yb-doped crystal hosts have been studied in the past decade, mostly to generate both high average powers and shorter pulses from ultrafast oscillators. However, this work only starts to be extended to large-optical bandwidth amplifiers, among others, Yb: SYS [8], and more recently Yb-doped fluorites Yb:CaF 2 [9–11]. The Yb:CALGO material stands out among gain media because it has the broadest emission cross-sections together with good thermal and mechanical properties [12–17]. Indeed, with a gain bandwidth of ∼60 nm spanning from 1010 to 1070 nm, it has already been used to generate sub-50-fs pulses from ultrafast oscillators. Its thermal conductivity of 6.3–6.9 W⋅K −1 for a 2%-doped matrix holds great promises with respect to average power scaling. In this Letter, we report on the first sub-100-fs regenerative amplifier based on an Yb-dope

Short pulse and high repetition rate Yb:CaF2 diode-pumped regenerative amplifier

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