The Experts below are selected from a list of 107643 Experts worldwide ranked by ideXlab platform
Razvan Stoian - One of the best experts on this subject based on the ideXlab platform.
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Ultrafast laser nanostructuring in bulk silica, a “slow” microexplosion
Optica, 2017Co-Authors: Manoj Bhuyan, Jean-philippe Colombier, Madhura Somayaji, Alexandre Mermillod-blondin, Florent Bourquard, Razvan StoianAbstract:Ultrafast laser microexplosions in bulk Material create extreme conditions at mesoscopic scales and are essential to the synthesis of extraordinary matter structural phases and to light structuring beyond the diffraction limit. Observing the Transformation cycle can elucidate their evolution. We discuss multiscale relaxation dynamics in the formation of nanoscale structures in laser-irradiated fused silica. Tightly focused ultrafast nondiffractive Bessel beams are used to generate microexplosions that lead to uniform voids. These trigger thermodynamic nonequilibrium conditions in one-dimensional geometries with record excitation confinement down to 100 nm and electronic pressures in the gigapascal range. Time-resolved phase-contrast microscopy on nanosecond to microsecond scales indicates that void formation is a slow process developing from low-viscosity phases after persistent plasma fluid stages signaled via nanosecond-long luminescence. The void evolution is not necessarily driven by rarefaction following initial pressure relaxation, but involves molecular kinetics and stress mechanisms that interfere with the evolution of the liquid phase and induce cavitation. Heat transport is also visualized. Higher energy leads to hydrodynamic instabilities and void fragmentation. The dynamic view helps us understand Material Transformation under confinement.
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Adaptive techniques for ultrafast laser Material processing
2016Co-Authors: Razvan StoianAbstract:Requirements for high accuracy in laser Material processing triggered a considerable amount of effort in investigating ultrashort pulse laser effects in structuring Materials on micro and nanoscales. Minimal energy diffusion and high nonlinearity of interaction indicate the possibility of confining energy on smallest spatial scales. The potential of inducing fast structural transitions and generating novel Material states with upgraded properties and functions makes ultrashort pulses instruments of choice for precision Transformation and structuring of Materials. The analyses of ablation phases, Material Transformation mechanisms, and, especially, their characteristic dynamics offer in turn the key to optimizing laser-matter interaction in view of various criteria related to laser processing: efficiency, accuracy, quality. This thesis summarizes previous works of the author on investigating static and dynamic effects of ultrafast laser energy deposition, with application in Material processing. The knowledge derived from the dynamic Material response indicates energy relaxation times as a guideline for synergetically improving the interaction between radiation and matter. This is achieved by adapting the incoming energy rate to the Material reaction time using newly developed techniques of spatio-temporal beam forming. Optimal coupling of energy gives the possibility to guide the Material response towards user-designed directions, offering extended flexibility for quality Material processing, and, perhaps, the necessary insight into developing “smart” processing technologies.
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Investigation and control of ultrafast laser-induced isotropic and anisotropic nanoscale-modulated index patterns in bulk fused silica
Optical Materials Express, 2013Co-Authors: Razvan Stoian, Konstantin Mishchik, Guanghua Cheng, Cyril Mauclair, Ciro D'amico, Jean-philippe Colombier, Marian ZamfirescuAbstract:Ultrafast laser-induced refractive index changes in a-SiO2 consist, depending on the irradiation conditions, of either positive variations, voids, or regular nanoscale patterns, each of these underlying specific structural Transformations. These allow for obtaining a large palette of optical functions ranging from low loss guiding to anisotropic scattering. While briefly reviewing the excitation mechanisms, we spectroscopically interrogate local electronic and structural Transformations of the glass in the isotropic index zones and in the regular self-organized nanostructures, indicating bond breaking and matrix oxygen deficiency. A spatial defect segregation marks the Material Transformation in the different photoinscription regimes. We equally propose a method of real time control of nanogratings formation under the action of ultrashort laser pulse with variable envelopes. Application as polarizing optical devices is discussed.
Konrad Wegener - One of the best experts on this subject based on the ideXlab platform.
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laser surface and subsurface modification of sapphire using femtosecond pulses
Applied Surface Science, 2016Co-Authors: Gregory Eberle, M Schmidt, Frank Pude, Konrad WegenerAbstract:Abstract Two methods to process sapphire using femtosecond laser pulses are demonstrated, namely ablation (surface), and in-volume laser modification followed by wet etching (subsurface). Firstly, the single and multipulse ablation threshold is determined and compared with previous literature results. A unique application of ablation is demonstrated by modifying the entrance aperture of water jet orifices. Laser ablation exhibits advantages in terms of geometric flexibility and resolution, however, defects in the form of edge outbreaks and poor surface quality are evident. Secondly, the role of Material Transformation, polarisation state and formation of multi-focus structures after in-volume laser modification is investigated in order to explain their influence during the wet etching process. Laser scanning and electron microscopy as well as electron backscatter diffraction measurements supported by ion beam polishing are used to better understand quality and laser-Material interactions of the two demonstrated methods of processing.
Jean-philippe Colombier - One of the best experts on this subject based on the ideXlab platform.
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Ultrafast laser nanostructuring in bulk silica, a “slow” microexplosion
Optica, 2017Co-Authors: Manoj Bhuyan, Jean-philippe Colombier, Madhura Somayaji, Alexandre Mermillod-blondin, Florent Bourquard, Razvan StoianAbstract:Ultrafast laser microexplosions in bulk Material create extreme conditions at mesoscopic scales and are essential to the synthesis of extraordinary matter structural phases and to light structuring beyond the diffraction limit. Observing the Transformation cycle can elucidate their evolution. We discuss multiscale relaxation dynamics in the formation of nanoscale structures in laser-irradiated fused silica. Tightly focused ultrafast nondiffractive Bessel beams are used to generate microexplosions that lead to uniform voids. These trigger thermodynamic nonequilibrium conditions in one-dimensional geometries with record excitation confinement down to 100 nm and electronic pressures in the gigapascal range. Time-resolved phase-contrast microscopy on nanosecond to microsecond scales indicates that void formation is a slow process developing from low-viscosity phases after persistent plasma fluid stages signaled via nanosecond-long luminescence. The void evolution is not necessarily driven by rarefaction following initial pressure relaxation, but involves molecular kinetics and stress mechanisms that interfere with the evolution of the liquid phase and induce cavitation. Heat transport is also visualized. Higher energy leads to hydrodynamic instabilities and void fragmentation. The dynamic view helps us understand Material Transformation under confinement.
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Investigation and control of ultrafast laser-induced isotropic and anisotropic nanoscale-modulated index patterns in bulk fused silica
Optical Materials Express, 2013Co-Authors: Razvan Stoian, Konstantin Mishchik, Guanghua Cheng, Cyril Mauclair, Ciro D'amico, Jean-philippe Colombier, Marian ZamfirescuAbstract:Ultrafast laser-induced refractive index changes in a-SiO2 consist, depending on the irradiation conditions, of either positive variations, voids, or regular nanoscale patterns, each of these underlying specific structural Transformations. These allow for obtaining a large palette of optical functions ranging from low loss guiding to anisotropic scattering. While briefly reviewing the excitation mechanisms, we spectroscopically interrogate local electronic and structural Transformations of the glass in the isotropic index zones and in the regular self-organized nanostructures, indicating bond breaking and matrix oxygen deficiency. A spatial defect segregation marks the Material Transformation in the different photoinscription regimes. We equally propose a method of real time control of nanogratings formation under the action of ultrashort laser pulse with variable envelopes. Application as polarizing optical devices is discussed.
Michael Wang - One of the best experts on this subject based on the ideXlab platform.
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model for the part manufacturing and vehicle assembly component of the vehicle life cycle inventory
Journal of Industrial Ecology, 2013Co-Authors: John Sullivan, Andrew Burnham, Michael WangAbstract:A model is presented for calculating the environmental burdens of the part manufacturing and vehicle assembly (VMA) stage of the vehicle life cycle. The model is based on a process‐level approach, accounting for all significant Materials by their Transformation processes (aluminum castings, polyethylene blow molding; etc.) and plant operation activities (painting; heating, ventilation, and air conditioning [HVAC], etc.) germane to VMA. Using quantitative results for these Material/Transformation process pairings, a percent‐by‐weight Material/Transformation distribution (MTD) function was developed that permits the model to be applied to a range of vehicles, both conventional and advanced (e.g., hybrid electric, light weight, aluminum intensive). Upon consolidation of all inputs, the model reduces to two terms: one proportional to vehicle mass and a plant overhead per vehicle term. When the model is applied to a Materially well‐characterized conventional vehicle, reliable estimates of cumulative energy consumption (34 gigajoules/vehicle) and carbon dioxide (CO) emissions (2 tonnes/vehicle) with coefficients of variation are computed for the VMA life cycle stage. Due to the more comprehensive coverage of manufacturing operations, our energy estimates are on the higher end of previously published values. Nonetheless, they are still somewhat underestimated due to a lack of data on overhead operations in part manufacturing facilities and transportation of parts and Materials between suppliers and vehicle manufacturing operations. For advanced vehicles, the Material/Transformation process distribution developed above needs some adjusting for different Materials and components. Overall, energy use and CO emissions from the VMA stage are about 3.5% to 4.5% of total life cycle values for vehicles.
Qu Song-sheng - One of the best experts on this subject based on the ideXlab platform.
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Thermogenetic curves and thermokinetics of seed germination of Robinia pseudoacaia
Journal of Forestry Research, 2001Co-Authors: Hu Yunchu, Zhou Jiang, Qu Song-shengAbstract:Seed germination process has closely relation with Material Transformation and energy exchange within the seed. Study on its thermal effect is important for understanding the mechanism and the influencing factors of the seed germination. The thermogenetic curves of seed germination ofRobinia pseudoacacia was measured by a new-type conductive microcalorimeter made in Wuhan University. The relationship was analyzed between the germination thermogenetic regulation and seed germination physiology. The thermogentic curves were further analyzed by thermokinetic theory to obtain the dynamic parameters and the thermokinetic model on seed germination ofRobinia pseudoacacia. The relationship of the thermogenetic power (μ w) and the germination time(h) of the germination process of 20 grainsRobinia pseudocacia seeds at 25°C wasP=208.77/[0.1937+0.8063exp(−0.06563t)]
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Thermogenetic curves and thermokinetics of seed germination of
2001Co-Authors: Hu Yunchu, Zhou Pei-jiang, Wang Cunxin, Qu Song-shengAbstract:Seed germination process has closely relation with Material Transformation and energy exchange within the seed. Study on its thermal effect is important for understanding the mechanism and the influencing factors of the seed germination. The thermogenetic curves of seed germination of Robinia pseudoacacia was measured by a new-type conductive microcalo- rimeter made in Wuhan University. The relationship was analyzed between the germination thermogenetic regulation and seed germination physiology. The thermogentic curves were further analyzed by thermokinetic theory to obtain the dynamic parameters and the thermokinetic model on seed germination of Robinia pseudoacacia. The relationship of the thermogenetic power( ~ w) and the germination time(h) of the germination process of 20 grains Robinia pseudocacia seeds at 25"C was /:'=208.77/(0.1937+0.8063exp(-0.06563 t))