Institute doptique dAquitaine
Institute doptique dAquitaine
Arnaud C.,Institute dOptique dAquitaine |
Almirall A.,Institute dOptique dAquitaine |
Loumena C.,Institute dOptique dAquitaine |
Kling R.,Institute dOptique dAquitaine
Journal of Laser Applications | Year: 2017
Conventional processes to polish metallic surfaces are usually manual or semiautomatic processes and offer very good results. However, these solutions are limited by the part geometry which can have angles or edges to preserve. Moreover, these solutions are time consuming for the operator and consumable parts have to be replaced frequently due to erosion. Lasers, on the other hand, offer a good alternative to polish and smooth metal surfaces, preserving the edges, and solving the accessibility problems. Fiber lasers are perfectly adapted to industrial applications because they are low cost, with high efficiency, high reliability, and can easily melt metals. In this paper, we report on the latest developments in structuring and polishing metals by surface remelting with common fiber lasers. We focus our work on polishing low and high surface roughness. Laser treatment of high roughness surfaces can considerably reduce processing time compared to conventional processes and offers prepolishing approach from 100 to 200 s/cm2. High reflective parts can be made from lower surface roughness to create bright appearance or medical instruments (from 20 to 90 s/cm2). In terms of results, we mostly concentrate our process optimization efforts on the solidification defaults, the structure modifications and reduction of Heat Affected Zone. Thus, laser polishing can be used for industrial solutions in polishing molds with applications in health care, watch industry, aeronautics, and many more. Commonly such patterns are created by laser ablation but this process uses more expensive lasers, with lower efficiency and reliability, and with longer processing time. Moreover, metal becomes matt finished. With high power laser, depending on the laser power and scanning strategy on the metal, the melting pool can be moved to create complex patterns. Experiments have shown that we can obtain a pattern with around 200 μm height at 40 s/cm2. Thus, creating patterns can be up to 30 times faster than for laser ablation processes. The created surface is, in this case, smooth with polished surface finish. © 2017 Laser Institute of America.
Jolly A.,Institute dOptique dAquitaine |
Jolly A.,CEA Cesta |
Vincont C.,Institute dOptique dAquitaine |
Boullet J.,Institute dOptique dAquitaine
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017
We propose an innovating model to describe the kinetics of competing photo-darkening and photo-bleaching phenomena in high-power, Ytterbium-Doped-Fibre-Amplifiers. This model makes use of aggregated species of trivalent Ytterbium and divalent ions, which operate as primarily efficient color-centers. This ensures multi-photon excitation, partly from the pump and partly from the signal. The fit of numerical computations with dedicated experiments help to validate our theoretical assumptions, in the definition of the involved physics. Potential applications of this study include further discussions for the selection of processing options with fibre-manufacturers and the optimization of operating conditions. © 2017 SPIE.
Gemini L.,Institute doptique dAquitaine |
Schmitz T.,University of Duisburg - Essen |
Kling R.,Institute doptique dAquitaine |
Barcikowski S.,University of Duisburg - Essen |
Gokce B.,University of Duisburg - Essen
ChemPhysChem | Year: 2017
The distinctive feature of upconverting compounds to absorb and emit light in the near-infrared region has made upconverting nanoparticles of great interest in various application fields. Nevertheless, these colloids show a highly hydrophobic behavior, and therefore, the use of a proper stabilizing agent is necessary in most cases. Although few chemical techniques for colloid stabilization are available, it is still difficult to achieve a fully reproducible synthesis method for stable upconverting nanoparticle colloids. In this work, upconversion 18 %Yb:1 %Er:NaYF4 nanoparticles were produced by ultrafast pulsed laser ablation in a water and 2-[2-(2-methoxyethoxy)- ethoxy]acetic acid (MEEAA) environment to assess the stabilization effect of the surfactant on the nanoparticle colloid properties. The effects of the laser fluence and MEEAA concentration on the nanoparticles′ properties were investigated by TEM, EDS, and emission spectra analyses. The results show that ultrashort pulsed laser ablation in liquid allows generating highly spherical nanoparticles with conserved stoichiometry and optical properties. Moreover, it is possible to obtain colloids with significantly higher stability and preserved optical properties by one-step PLAL processes directly in the MEEAA environment. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Jolly A.,Institute Doptique Daquitaine |
Jolly A.,CEA Cesta |
Vincont C.,Institute Doptique Daquitaine |
Pierre C.,Institute Doptique Daquitaine |
Boullet J.,Institute Doptique Daquitaine
Applied Physics B: Lasers and Optics | Year: 2017
We propose an innovative, fully space–time model to take into account the seed-dependent nature of ageing penalties in high-power ytterbium-doped fibre amplifiers. Ageing is shown to be based on the on-going competition between photo-darkening and photo-bleaching phenomena. Our approach is based on the natural interplay between the excited states of co-existing ytterbium pairs and colour centres in highly doped fibres, in the presence of thermal coupling between the closely spaced excited states. As initiated from IR photons, the excitation of colour centres up to the UV band is supposed to be governed by multi-photon absorption. The interactions of interest in the kinetics of photo-bleaching then take the form of highly efficient charge transfers, which imply the reduction of some fraction of the basically trivalent ions to their divalent state. Due to the activation of ytterbium pairs by means of energy transfer up-conversion, these interactions get more and more effective at elevated operating powers. Computational results using these principles actually help to fit our experimental data regarding seeding effects, as well as fully generic trends already evidenced in the literature. This gives a fine demonstration for the need to discriminate co-active pump and signal contributions. Our self-consistent, still simplified model then consists of a valuable tool to help for a deeper understanding of the ageing issues. Furthermore, considering higher-order ytterbium aggregates, this should open new routes towards more comprehensive models. © 2017, Springer-Verlag GmbH Germany.
Schembri F.,CNRS Laboratory of Future |
Schembri F.,Institute dOptique dAquitaine |
Bodiguel H.,CNRS Laboratory of Future |
Colin A.,CNRS Laboratory of Future
Soft Matter | Year: 2015
We report the development and analysis of a velocimetry technique based on the short time displacement of molecular tracers, tagged thanks to photobleaching. We use confocal microscopy to achieve a good resolution transverse to the observation field in the direction of the velocity gradient. The intensity profiles are fitted by an approximate analytical model which accounts for hydrodynamic dispersion, and allow access to the local velocity. The method is validated using pressure driven flow in microfluidic slits having a thickness of a few tens of micrometers. We discuss the main drawbacks of this technique which is an overestimation of the velocity close to the walls due to the combination of molecular diffusion and shear. We demonstrate that this error, limited to a near wall region of a few micrometers thick, could be controlled by limiting the diffusion of fluorophore molecules or minimizing the bleaching time. The presented technique could be combined with standard particle imaging velocimetry to access velocity differences and allow particle trajectory analysis in microflows of suspensions. This journal is © The Royal Society of Chemistry.
Lozan O.,French National Center for Scientific Research |
Perrin M.,French National Center for Scientific Research |
Ea-Kim B.,CNRS Charles Fabry Laboratory |
Rampnoux J.M.,French National Center for Scientific Research |
And 2 more authors.
Physical Review Letters | Year: 2014
In this Letter, we study the heat dissipated at metal surfaces by the electromagnetic field scattered by isolated subwavelength apertures in metal screens. In contrast to the common belief that the intensity of waves created by local sources should decrease with the distance from the sources, we reveal that the dissipated heat at the surface remains constant over a broad spatial interval. This behavior that occurs for noble metals at near infrared wavelengths is observed with nonintrusive thermoreflectance measurements and is explained with an analytical model, which underlines the intricate role played by quasicylindrical waves in the phenomenon. Additionally, we show that, by monitoring the phase of the quasicylindrical waves, the total heat dissipated at the metal surface can be rendered substantially smaller than the heat dissipated by the launched plasmon. This interesting property offers an alternative to amplification for overcoming the loss issue in miniaturized plasmonic devices. © 2014 American Physical Society.
Jolly A.,Institute dOptique dAquitaine |
Jolly A.,CEA Cesta |
Gokhan F.S.,Hasan Kalyoncu University |
Bello R.,Institute dOptique dAquitaine |
Dupriez P.,Institute dOptique dAquitaine
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014
We present a comprehensive experimental study of the technique of Longitudinal Mode Filling (LMF) applied to the reduction of Stimulated Brillouin Scattering (SBS), in Ytterbium Doped Fibre Amplifiers (YDFA) at the wavelength of 1064 nm. Pulse durations and Mode Field Diameters (MFD) lie in the ranges of 10 - 100 ns and 10 - 35 μm, respectively. Input pulse-shaping is implemented by means of direct current modulation in multimode Laser-Diode seeds. This evidences a number of interests in the development of robust and low cost Master Oscillator Power Amplifiers (MOPA). Highly energetic, but properly shaped, nanosecond pulses may be produced this way without any need of additional electro-optical means for in-line phase and amplitude modulation. Seeds consist of Distributed Feed- Back (DFB) and Fibre Bragg Gratings (FBG) with different fibre lengths. We demonstrate the benefit of LMF with properly controlled mode spacing, in combination with chirp effects due to fast current transients in the semiconductors, in order to deal with SBS thresholds in the range of a few to some hundred μJ. The variations of the SBS threshold are discussed versus the number of longitudinal modes, the operating conditions of the selected seed and pulse-shaping conditions. © 2015 SPIE.
Refregier Ph.,École Centrale Marseille |
Wasik V.,École Centrale Marseille |
Vynck K.,ESPCI ParisTech |
Vynck K.,Institute DOptique DAquitaine |
Carminati R.,ESPCI ParisTech
Optics Letters | Year: 2014
The theory of the intrinsic coherence, originally developed for 2D fields, is generalized in order to analyze coherence properties of light with a polarization that can fluctuate in three dimensions. Several notions, such as the concept of mean-square coherence and the capacity to describe irreversible behaviors, are demonstrated and illustrated with the example of light in 3D disordered media with frozen and nonfrozen disorders. © 2014 Optical Society of America.
Zoubir A.,Institute Doptique Daquitaine |
Dupriez P.,Institute Doptique Daquitaine
European Physical Journal: Special Topics | Year: 2015
The concept of massively parallel coherent fiber lasers holds great promise to generate enormous laser peak power in order to produce highly energetic particle beams. Such technology is expected to provide a route to practical particle colliders or to proton generation for medical applications. Such concept is based on the phasing of thousands of fiber amplifiers each emitting mJ level pulses, in which optical fibers are key components. In this paper, we present important technological building blocks based on optical fibers, which could pave the way for efficient, compact and cost-effective components to address the technological challenges ahead. © 2015, EDP Sciences and Springer.
Aguergaray C.,Institute dOptique dAquitaine
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016
We demonstrate herein a PM-fiber based cavity design capable of supporting many different pulse dynamics, such as soliton propagation or dissipative solitons in a dispersion managed cavity. By changing the dispersion of the fiber Bragg grating of the cavity we modify the net cavity dispersion, and thus stimulate various pulse dynamics. In particular we demonstrate the first net normal cavity, all-PM, all-fiber, dipersion managed cavity operating the in the 2μm range. Furthermore, we also demonstrate an all-fiber all-PM MOPA system capable of delivering up to 6 W of average power at 16 MHz by direct amplification of 70 ps long narrowband pulses. The amplifier stages are not fully saturated and are currently limited by the pump power available. © 2016 SPIE.