Michel Meunier

Synthesis of colloidal nanoparticles during femtosecond laser ablation of gold in water

Femtosecond laser radiation has been used to ablate a gold target in pure deionized water to produce colloidal gold nanoparticles. We report evidence for two different mechanisms of material ablation in the liquid environment, whose relative contributions determine the size distribution of the produced particles. The first mechanism, associated with thermal-free femtosecond ablation, manifests itself at relatively low laser fluences F<400 J/cm2 and leads to very small (3–10 nm) and almost monodispersed gold colloids. The second one, attributed to the plasma-induced heating and ablation of the target, takes place at high fluences and gives rise to a much larger particle size and broad size distribution. The fabricated nanoparticles exhibit plasmon-related optical absorption peak and are of significance for biosensing applications.

A transformer model for winding fault studies

This paper deals with a method of modeling internal faults in a power transformer. The method leads to a model which is entirely compatible with EMTP software. It enables simulation of faults between any turn and the earth or between any two turns of the transformer windings. Implementation of the proposed method assumes knowledge of how to evaluate the leakage factors between the various coils of the transformer. A very simple method is proposed to evaluate these leakage factors. At last, an experimental validation of the model allows the estimation of its accuracy. >

Laser precision microfabrication

Process Control in Laser Material Processing for the Micro and Nanometer Scale Domains.- Theory and Simulation of Laser Ablation - from Basic Mechanisms to Applications.- Laser Devices and Optical Systems for Laser Precision Microfabrication.- Fundamentals of Laser-Material Interaction and Application to Multiscale Surface Modification.- Temporal Pulse Tailoring in Ultrafast Laser Manufacturing Technologies.- Laser Nanosurgery, Manipulation, and Transportation of Cells and Tissues.- Laser Synthesis of Nanomaterials.- Ultrafast Laser Micro- and Nanostructuring.- 3D Fabrication of Embedded Microcomponents.- Micromachining and Patterning.- Laser Transfer Techniques for Digital Microfabrication.- Hybrid Laser Processing of Transparent Materials.- Drilling, Cutting, Welding, Marking and Microforming.

Surface plasmon resonance detection of E. coli and methicillin-resistant S. aureus using bacteriophages.

Early diagnosis and appropriate treatment of Escherichia coli (E. coli) O157:H7 and methicillin-resistant Staphylococcus aureus (MRSA) are key elements in preventing resultant life-threatening illnesses, such as hemorrhagic colitis, hemolytic uremic syndrome, and septicemia. In this report, we describe the use of surface plasmon resonance (SPR) for the biodetection of pathogenic bacteria, using bacteriophages as the recognition elements. T4 bacteriophages were used to detect E. coli, while a novel, highly specific phage was used to detect MRSA. We found that the system permits label-free, real-time, specific, rapid and cost-effective detection of pathogens, for concentrations of 10(3) colony forming units/milliliter, in less than 20 min. This system promises to become a diagnostic tool for bacteria that cause major public concern for food safety, bioterrorism, and nosocomial infections.

Operating Conditions of a Single-Chamber SOFC

Single-chamber cells of two different types have been operated between 700 and 800°C in various methane-air mixtures. These cells are made mostly of conventional materials for solid oxide fuel cells (SOFCs), strontium-doped lanthanum manganite, yttria-stabilized zirconia (YSZ), and Ni-YSZ cermet. One type is electrolyte-supported, while the other represents a state-of-the-art fabrication for anode-supported cells. The anode-supported cells operate in a narrower range of methane-air ratios, but offer remarkable maximum specific powers, 360 and 285 mW/cm 2 at 800 and 700°C, respectively. Some theoretical considerations about the actual operation of these cells are also provided.

Off-resonance plasmonic enhanced femtosecond laser optoporation and transfection of cancer cells

A femtosecond laser based transfection method using off-resonance plasmonic gold nanoparticles is described. For human cancer melanoma cells, the treatment leads to a very high perforation rate of 70%, transfection efficiency three times higher than for conventional lipofection, and very low toxicity (<1%). Off-resonance laser excitation inhibited the fracture of the nanoparticles into possibly toxic DNA intercalating particles. This efficient and low toxicity method is a promising alternative to viral transfection for skin cancer treatment.

Prony's method: an efficient tool for the analysis of earth fault currents in Petersen-coil-protected networks

Pronys method is a technique for estimating the modal components present in a signal. Every modal component is defined by four parameters frequency, magnitude, phase, and damping. This method is used to analyse earth fault currents in Petersen-coil-protected 20 kV networks. The variations of Pronys parameters in terms of some of the power systems characteristics (distance between the busbar and the fault, fault resistance and capacitive current of the whole network) are presented. It is shown that some of the Pronys parameters relating to the fault current transient may be useful to determine what kind of fault occurred, and where it occurred. >

Plasma Mediated off-Resonance Plasmonic Enhanced Ultrafast Laser-Induced Nanocavitation

The generation of nanobubbles around plasmonic nanostructures is an efficient approach for imaging and therapy, especially in the field of cancer research. We show a novel method using infrared femtosecond laser that generates ≈800 nm bubbles around off-resonance gold nanospheres using 200 mJ/cm(2) 45 fs pulses. We present experimental and theoretical work that demonstrate that the nanobubble formation results from the generation of a nanoscale plasma around the particle due to the enhanced near-field rather than from the heating of the particle. Energy absorbed in the nanoplasma is indeed more than 11 times the energy absorbed in the particle. When compared to the usual approach that uses nanosecond laser to induce the extreme heating of in-resonance nanoparticles to initiate bubble formation, our off-resonance femtosecond technique is shown to bring many advantages, including avoiding the particles fragmentation, working in the optical window of biological material and using the deposited energy more efficiently.

Fragmentation of colloidal nanoparticles by femtosecond laser-induced supercontinuum generation

A femtosecond laser-based method to control the size characteristics of gold colloidal nanoparticles is reported. The method uses the supercontinuum generation produced through a strong nonlinear-optical interaction of the femtosecond radiation with a liquid to fragment relatively large colloids and reduce their agglomeration. The fragmented species then recoalesce to form smaller, less dispersed, and much more stable nanoparticles in the solution. The size of the nanoparticles after the treatment is independent of the initial characteristics of colloids, but depends strongly on laser parameters and on the presence of chemically active species in the solution.

Properties and sensing characteristics of surface-plasmon resonance in infrared light

Conditions of surface-plasmon resonance (SPR) production with use of IR pumping light (800-2300 nm) in the Kretschmann-Raether prism arrangement were investigated. Both calculations and experimental data showed that SPR characteristics in the IR are strongly influenced by the properties of the coupling prism material. Indeed, quite different regularities of plasmon excitation, polarity of sensing response, and sensitivity are observed for two different glasses and silicon. The observed differences in SPR properties are related to essentially different behavior of dispersion characteristics of materials near the SPR coupling point. Methods for improving sensor performance and miniaturizing the SPR technique using novel coupling materials (silicon) are discussed.