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Lopez J.,French National Center for Scientific Research | Torres R.,Alphanov | Zaouter Y.,Amplitude Systemes | Georges P.,Institute Optique Graduate School | And 3 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Ultrafast laser are well known to provide cold ablation on metals at near-threshold fluence and low repetition rate. However increasing the repetition rate from multi-kHz to MHz may produce a heat accumulation in the target depending on both the scanning speed and the material properties. This potentially leads to two effects: enhanced ablation efficiency as well as increased heat affected zone. To identify potentials and limitations while maintaining highest processing quality is the main objective of this paper and a key issue for many industrial applications. We present some comprehensive results on the influence of both repetition rate and pulse duration on the ablation efficiency. This investigation is performed using a new generation of high power Ytterbium doped fiber ultrafast laser with a tunable pulse duration ranging from 350fs to 10ps and with repetition rate going from 250kHz to 2MHz. The output power is up to 40 watt. The effect of both parameters above on ablation efficiency of Al, Cu and Mo is discussed with respect to removal rate measurement and SEM analysis. © 2013 Copyright SPIE.


Kling R.,Alphanov | Dijoux M.,Alphanov | Romoli L.,University of Pisa | Tantussi F.,University of Pisa | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Trepanning heads are well known to be efficient in high aspect drilling and to provide a precise control of the hole geometry. Secondly, femtosecond lasers enable to minimize the heat effects and the recast layer on sidewalls but are typically used on thin sheet. The combination of both present a high potential for industrial applications such as injector or cooling holes where the bore sidewall topology has a major influence on the dynamics of the gas flow. In this paper we present results using this combination. The effect of pulse energy, repetition rate and revolution speed of the head on both geometry and roughness are discussed. The quality of the sidewall is checked by roughness measurement and by metallographic analysis (SEM; chemical etching, micro hardness). © 2013 SPIE.


Jolly A.,ALPhANOV | Jolly A.,CEA Cesta | Gokhan F.S.,Hasan Kalyoncu University | Bello R.,ALPhANOV | Dupriez P.,ALPhANOV
Optics Express | Year: 2014

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 10μm-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 μJ. 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. © 2014 Optical Society of America.


Mincuzzi G.,Alphanov | Gemini L.,Alphanov | Faucon M.,Alphanov | Kling R.,Alphanov
Applied Surface Science | Year: 2016

Surface texturing by Ultra-Short Pulses Laser (UPL) for industrial applications passes through the use of both fast beam scanning systems and high repetition rate, high average power P, UPL. Nevertheless unwanted thermal effects are expected when P exceeds some tens of W. An interesting strategy for a reliable heat management would consists in texturing with a low fluence values (slightly higher than the ablation threshold) and utilising a Polygon Scanner Heads delivering laser pulses with unrepeated speed. Here we show for the first time that with relatively low fluence it is possible over stainless steel, to obtain surface texturing by utilising a 2 MHz femtosecond laser jointly with a polygonal scanner head in a relatively low fluence regime (0.11 J cm−2). Different surface textures (Ripples, micro grooves and spikes) can be obtained varying the scan speed from 90 m s−1 to 25 m s−1. In particular, spikes formation process has been shown and optimised at 25 m s−1 and a full morphology characterization by SEM has been carried out. Reflectance measurements with integrating sphere are presented to compare reference surface with high scan rate textures. In the best case we show a black surface with reflectance value < 5%. © 2016 Elsevier B.V.


Mincuzzi G.,Alphanov | Fleureau M.,Alphanov | Faucon M.,Alphanov | Kling R.,Alphanov
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

The combination of both, fast beam scanning systems and high repetition rate, high average power lasers, represents an interesting technological solution for surface texturing by Ultra-Short Pulses Laser to gain a foothold into industrial environment for commercial purposes. Nevertheless unwanted thermal effects are expected when the average power exceeds some tens of W. An interesting strategy for a reliable heat management would consists of texturing surfaces with a low fluence values (slightly higher than the ablation threshold) and utilising a polygon scanning head which is able to deflect the laser beam with unprecedented speed. Here we show that over stainless steel, it is possible to obtain different surface textures (in particular ripples, micro grooves and spikes) by utilising a 2 MHz femtosecond laser jointly with a fast and accurate polygonal scanner head at relatively low fluence (0.11 J·cm-2). The evolution of the Laser induced surface structures morphology is shown when varying the scan speed between 25 m·s-1 and 90 m·s-1. Two different wavelengths have been utilised for the process λ= 1030 nm and λ = 515 nm and the difference of the results obtained have been highlighted. Moreover, a full structures morphology characterization by SEM has been carried out for all the textured surfaces. Finally, by increasing the number of successive surface scans is possible to tailor the surface reflectivity. As a result an average reflectivity value of < 5% over the visible range has been extracted from a blackened stainless steel surface. © 2016 SPIE.


Faucon M.,Alphanov | Laffitte A.,Alphanov | Lopez J.,Alphanov | Lopez J.,French Atomic Energy Commission | Kling R.,Alphanov
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The interaction between laser pulses and material surface can generate sub-wavelength surface structures named ripples. The used of ultrashort laser pulses avoid thermal effect in the lattice so the structures generated are well preserved and can be observed on various materials as metals, polymers or crystals. With increasing energy deposit, ripples grow to give cone-shape structures named spikes. All these structures are interesting to give special properties to the treated surface as coloration change, improvement of light absorption or modification of wettability properties. These structure generation process is well known for femtosecond Ti:Sa laser with a pulse duration below 100fs and repetition rates in the range of 10 kHz. However, to be relevant for industrial applications, the average power of the laser is a critical parameter. The emergence of new femtosecond Yb doped fiber lasers with pulse duration below 350fs permits an increase of the average power for a few years. We will present our latest results obtained for surface texturation on various metals such as stainless steel, titanium, aluminum and copper with these up to date laser source. We study the influence of the average power and of the repetition rate up to 1000 kHz on the surface structures generated on scanned areas. We obtain light reflexion below 7% on stainless steel and below 5% on titanium from 200nm to 2000nm. The characterizations of the results are done with SEM imaging, optical profilometry and with a spectrophotometer. © 2014 SPIE.


Bessou M.,University of Bordeaux 1 | Duday H.,University of Bordeaux 1 | Caumes J.-P.,Museum of Aquitaine | Salort S.,ALPhANOV | And 4 more authors.
Optics Communications | Year: 2012

Terahertz imaging and conventional X-ray have been used to investigate a sealed Ancient Egyptian jar preserved at the Museum of Aquitaine (France). Terahertz radiation revealed an unknown content that could not have been visualized by X-ray. By comparison with a model object, we concluded that this content was composed of organic materials explaining their relative radiolucency. © 2012 Elsevier B.V. All rights reserved.


Gemini L.,ALPhANOV | Hernandez M.-C.,ALPhANOV | Kling R.,ALPhANOV
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2016

Pulsed laser ablation in liquid (PLAL) is nowadays gaining popularity as innovative, reliable and efficient technique to produce high-purity nanoparticles (NPs) of many inorganic and organic materials. In this context, attention has been recently focused on luminescent up-conversion NPs (UCNPs) which, being characterized by sharp emission bands in ultraviolet (UV)-to-near-infrared (NIR) range upon NIR irradiation, are in fact of great interest in many biological and biomedical applications. Moreover, with respect to organic dyes NPs and quantum dots, UCNPs show less toxicity, increased chemical stability, long-lifetime decays and lack of photo-bleaching. Our research focuses on generation of UCNPs of rare earth lanthanide-doped crystalline material, namely 18%Yb:1%Er:NAYF4, by PLAL in water. It is well known that optical properties of NPs strongly depend on their features, as for instance size and shape, which in turn may be controlled by laser ablation parameters. Therefore, two different laser sources are used for the ablation processes in order to find the set of laser parameter, i.e. pulse duration, laser fluence and repetition rate, for which the luminescence of UPNPs is optimized: (i) Amplitude Satsuma HP3 system: 330 fs pulse duration, 1030 wavelength and (ii) Eolite Hegoa system: 50 ps pulse duration, 1030 nm wavelength. UCNPs are finally characterized by spectrophotometer analyses to define emission range and intensity under NIR light and by transmission electron microscopy (TEM) to determine their size and shape. © 2016 SPIE.


Wipliez L.,Alphanov | Lebrun L.,Alphanov | Kling R.,Alphanov | Fortunier P.,Micel | Fries L.,Micel
Journal of Laser Applications | Year: 2016

In printed electronics, such as organic photovoltaic or organic light-emitting diode display and lighting, a transparent conductive oxide layer has to be designed to delimit the size and shape of the final device. The most commonly used material is indium tin oxide (ITO). ITO has however many downsides such as resource scarcity, expensive processing, and brittleness (especially on flexible substrates). Silver nanowires are a promising alternative to overcome these issues, although optimization is still needed to reach ITO performance in terms of transparency and conductivity. In this study, the laser process has to remove the silver nanowire layer in order to obtain an electrical isolation: no remaining bridges in the scribe due to recast material or incomplete removal can be tolerated. Laser ablation of this transparent conductive thin film deposited on polyethylene terephthalate has been investigated using an ultrafast laser source. Pulse energy and scan speed were varied to determine their influence on depth selectivity and process window. The profiles of the selectively ablated area were studied with optical, confocal, and scanning electron microscopy. Compared to irradiation through the substrate, it was shown that front side irradiation allows a much larger process window. In the latter configuration, a fluence ranging from 0.22 to 15.8 J/cm2 and a scanning speed from 200 to 3000 mm/s, at a fixed frequency of 200 kHz, allowed a clean removal of silver nanowires. Using these parameters, isolated squares were scribed and electrical resistance was measured between the inside and the outside of the squares. A good electrical isolation (>20 MΩ) proved the successful removal of the silver nanowire layer using picosecond laser pulses, at a wavelength of 532 nm. © 2016 Laser Institute of America.


Lopez J.,Alphanov | Lopez J.,University of Bordeaux 1 | Kling R.,Alphanov | Torres R.,Alphanov | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

In order to minimize thermal load to the workpiece pico- and femtosecond lasers gain an increasing market share in industrial applications such as surface structuring or thin film selective ablation. Due to nonlinear absorption they are capable to process any type of material (dielectrics, semiconductors, metals) and provide an outstanding quality suppressing heat affects on the workpiece. In this paper, we report on results about surface engraving of metals (Al, Cu, Mo, Ni), semiconductor (Si) and polymer (PC) using a picosecond thin disk Yb:YAG-amplifier, which could be used in the picosecond regime as well as in the femtosecond regime by simply changing the seed laser source. In the picosecond regime the oscillator pulses, ranging from 10 to 34ps, can be directly amplified which leads to a quite simple and efficient amplifier architecture. On the other hand, a broadband femtosecond oscillator and a CPA configuration can be used in order to obtain pulse duration down to 900fs. We compare these results to recently obtained achievements using commercial femtosecond lasers based on Yb-doped crystals and fibers and operating at comparable output power levels, up to 15Watt. Finally, we have considered etch rate and process efficiency for both ps- and fs-regimes as a function of average power, of fluence and of intensity. © 2012 SPIE.

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