Génération d'impulsions ultrabrèves de haute puissance et a haut taux de répétition par amplification fibrée en régime auto-similaire ou d'auto-modulation de phase

Nous démontrons l’amplification d’impulsions pico- et femto-secondes par un dispositif fibré à un taux de répétition de 1 GHz obtenu par utilisation d’un VECSEL passivement mode-locké. Deux régimes non-linéaires d’amplification sont alors clairement mis en évidence, l’un dominé par l’auto-modulation de phase et l’autre par une évolution autosimilaire. Ce dernier régime conduit après recompression temporelle à des impulsions en limite de Fourier avec une durée temporelle inférieure à 150 fs

Nonlinear compression of high energy fiber amplifier pulses in air-filled hypocycloid-core Kagome fiber

International audienceWe report on the generation of 34 fs and 50 µJ pulses from a high energy fiber amplifier system with nonlinear compression in an air-filled hypocycloid-core Kagome fiber. The unique properties of such fibers allow bridging the gap between solid core fibers-based and hollow capillary-based post-compression setups, thereby operating with pulse energies obtained with current state-of-the-art fiber systems. The overall transmission of the compression setup is over 70%. Together with Yb-doped fiber amplifier technologies, Kagome fibers therefore appear as a promising tool for efficient generation of pulses with durations below 50 fs, energies ranging from 10 to several hundreds of µJ, and high average powers

Focus EMU, February 22, 2005

Une opinion rédigée et transmise à la Première ministre et aux Ministresprésidents régionaux par un collectif de signataires

Waarnemingen.be : non-native plant and animal occurrences in Flanders and the Brussels Capital Region, Belgium

Citizen scientists make important contributions to the collection of occurrence data of non-native species. We present two datasets comprising more than 520,000 records of 1,771 non-native species from Flanders and the Brussels Capital Region in Belgium, Western Europe, collected through the website http://www.waamemingen.be hosted by Stichting Natuurinformatie and managed by the nature conservation NGO Natuurpunt. Most records were collected by citizen scientists, mainly since 2008. Waarnemingen.be aims at recording all species, native and non-native, and it is shown here that this kind of biodiversity portals are also particularly well suited to collect large amounts of data on non-native species. Both datasets presented here are also discoverable through the Global Biodiversity Information Facility (GBIF)

Advanced high-power pulsed fibre laser systems and their applications

In this thesis, I report experimental studies towards power scaling of ultrashort fibre-based sources designed for applications including high average power femtosecond pulse generation and nonlinear frequency conversion. While the power produced by rare-earth doped fibre lasers operating in continuous-wave has dramatically increased within a few years to exceed the kilowatt level, pulsed fibre sources have been limited to tens of watts due to the onset of nonlinearities in fibre amplifiers. Therefore the aim is to manage fibre nonlinearities to achieve specific output properties at high average power. An innovative aspect of this work lies in the remarkable combination of telecom-grade semiconductor laser sources and high-power Yb-doped fibre amplifier technologies to produce short pulses at very high average power. Fibre nonlinear effects are often detrimental to the performance of fibre systems but can also provide an attractive tool to generate new useful wavelengths. The final part of this thesis describes efficient white light generation produced by a microstructure fibre pumped by the previously described green fibre source. Furthermore, I investigated a novel fibre source configuration for guide star application. The source I developed produced 1W at 589 nm through frequency doubling of 1178 nm radiation produced by pulsed Raman amplification in an Yb-doped fibre amplifier

SBS management in Yb-fiber-amplifiers using multimode seeds and pulse-shaping

We present a comprehensive analysis of the technique of Longitudinal-Mode-Filling (LMF) to reduce Stimulated Brillouin Scattering (SBS) limitations in Ytterbium Doped Fibre Amplifiers (YDFA), for the generation of nanosecond, temporally shaped pulses. A basic Master-Oscillator-Power-Amplifier (MOPA) system, comprising an output YDFA with 10 mu m-core active fibre, is experienced for benchmarking purposes. Input pulse-shaping is operated thanks to direct current modulation in highly multimode laser-diode seeds, either based on the use of Distributed Feed-Back (DFB) or of a Fibre Bragg Grating (FBG). These seeds enable wavelength control. We verify the effectiveness of the combination of LMF, with appropriate mode spacing, in combination with natural chirp effects from the seed to control the SBS threshold in a broad range of output energies, from a few to some tens of mu J. These variations are discussed versus all the parameters of the laser system. In accordance with the proposal of a couple of basic principles and with the addition of gain saturation effects along the active fibre, we develop a full-vectorial numerical model. Fine fits between experimental results and theoretical expectations are demonstrated. The only limitation of the technique arises from broadband beating noise, which is analysed thanks to a simplified, but fully representative description to discuss the signal-to-noise ratio of the amplified pulses. This provides efficient tools for application to the design of robust and cost-effective MOPAs, aiming to the generation of finely shaped and energetic nanosecond pulses without the need for any additional electro-optics. (C) 2014 Optical Society of Americ

Millijoule high-peak power narrow-linewidth sub-hundred nanosecond pulsed fibre MOPA at 1.55 microns

A millijoule, high-peak power, sub-hundred nanosecond pulse, fibre master-oscillator power-amplifier (MOPA) source with narrow linewidth output is presented. In addition, fibre MOPA design challenges and system limitations are discussed

High average power and high energy transport of femtosecond pulses with a low loss Kagome hollow-core photonic crystal fiber for micromachining

International audienc