The Experts below are selected from a list of 21636 Experts worldwide ranked by ideXlab platform
A. Vella - One of the best experts on this subject based on the ideXlab platform.
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effect of Laser Illumination on the electrical conductivity of single crystal diamond needles
Journal of Applied Physics, 2019Co-Authors: L. Arnoldi, M Borz, I Blum, Victor I Kleshch, A N Obraztsov, A. VellaAbstract:Herein, we present the results of electrical conductivity studies of single-crystal diamond needles. Pyramid-shaped needles of about hundreds of micrometers in length and about tens of micrometers in thickness were produced by oxidation of polycrystalline diamond films fabricated by chemical vapor deposition. The electrical conductivity of the needles was characterized via current measurements using a field ion microscope in the dark and under Laser Illumination. Considering the effects of Laser intensity and wavelength on the measured current, we determine that the observed conduction regime corresponds to competing Ohmic and Poole-Frenkel conduction mechanisms. The measured values are in good agreement with the values reported previously for bulk and thin film diamond. The model that is proposed explains the electric conduction properties as well as light absorption and subsequent sample heating, with the presence of structural defects and impurities in diamond.Herein, we present the results of electrical conductivity studies of single-crystal diamond needles. Pyramid-shaped needles of about hundreds of micrometers in length and about tens of micrometers in thickness were produced by oxidation of polycrystalline diamond films fabricated by chemical vapor deposition. The electrical conductivity of the needles was characterized via current measurements using a field ion microscope in the dark and under Laser Illumination. Considering the effects of Laser intensity and wavelength on the measured current, we determine that the observed conduction regime corresponds to competing Ohmic and Poole-Frenkel conduction mechanisms. The measured values are in good agreement with the values reported previously for bulk and thin film diamond. The model that is proposed explains the electric conduction properties as well as light absorption and subsequent sample heating, with the presence of structural defects and impurities in diamond.
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Ion energy spread in Laser-assisted atom probe tomography
EDP Sciences IOP Publishing and Società Italiana di Fisica, 2015Co-Authors: N. Sévelin-radiguet, F Vurpillot, B Deconihout, L. Arnoldi, A. Normand, A. VellaAbstract:A dedicated setup has been developed to measure with precision the appearance energy of field evaporated ions in Laser-assisted atom probe. Energy spreads down to 0.5 eV can be measured on different materials under different experimental conditions (electric field and Laser Illumination). Looking at each possible contributions, we show that this energy spread depends on the material and that it is due to the field evaporation process itself and especially to temperature-induced surface diffusion and electric-field strength in the case of metals and low-band-gap materials. For large-band-gap materials, a dependence on the Laser Illumination is shown
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field evaporation mechanism of bulk oxides under ultra fast Laser Illumination
Journal of Applied Physics, 2011Co-Authors: A. Vella, Baishakhi Mazumder, G Da Costa, B DeconihoutAbstract:The controlled field evaporation of single atoms from an oxide surface assisted by ultra fast Laser pulses has recently been demonstrated. When UV light is used, a photoionization mechanism was proposed. However, experimental results observed when the Laser intensity and wavelength are changed cannot be explained by this mechanism. Instead, a thermal assisted evaporation mechanism characterized by two evaporation times is proposed. The fast and slow evaporation rates are associated to two cooling processes inside the tip sample. Experiments are carried out on TiO2 and MgO field emitter tips to check the dependence of the evaporation process on structural properties of the oxide. A good agreement between the predictions of our model and the experimental data is found.
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three dimensional thermal response of a metal subwavelength tip under femtosecond Laser Illumination
Physical Review B, 2011Co-Authors: J Houard, F Vurpillot, A. Vella, B DeconihoutAbstract:The current work investigates numerically and experimentally the three-dimensional (3D) thermal response of a subwavelength tip illuminated by an ultrashort Laser pulse. A model is developed on the nanometric scale to predict the 3D tip temperature evolution from the initial Laser irradiation through the thermal equilibrium (several nanoseconds). The evolution of the ion temperature is experimentally monitored by atom probe tomography. The anisotropic ion emission observed on steel specimens illuminated with an ultrashort Laser and the evaporation behavior of amorphous glasses is predicted by our 3D thermal model.
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thermal response of a field emitter subjected to ultra fast Laser Illumination
Journal of Physics D, 2009Co-Authors: F Vurpillot, A. Vella, J Houard, B DeconihoutAbstract:Using an ultra-fast Laser assisted atom probe, the temporal evolution of the temperature of a tungsten field emitter subjected to Illumination is studied. The combination of pump probe experiments and evaporation rate measurements is used to estimate the duration of field evaporation, the induced peak temperature and the cooling time. The main conclusion of the measurements is that, despite a significant heating of the tip by the Laser pulse, the cooling time is anomalously fast, below 0.5 ns. Hence, thermal effects are considered to play a major role in ion emission in contrast to conclusions of our previous works. It is shown that the really fast anomalous cooling rate can only be related to a confined heating zone at the tip apex smaller than the wavelength of the Laser.
B Deconihout - One of the best experts on this subject based on the ideXlab platform.
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Ion energy spread in Laser-assisted atom probe tomography
EDP Sciences IOP Publishing and Società Italiana di Fisica, 2015Co-Authors: N. Sévelin-radiguet, F Vurpillot, B Deconihout, L. Arnoldi, A. Normand, A. VellaAbstract:A dedicated setup has been developed to measure with precision the appearance energy of field evaporated ions in Laser-assisted atom probe. Energy spreads down to 0.5 eV can be measured on different materials under different experimental conditions (electric field and Laser Illumination). Looking at each possible contributions, we show that this energy spread depends on the material and that it is due to the field evaporation process itself and especially to temperature-induced surface diffusion and electric-field strength in the case of metals and low-band-gap materials. For large-band-gap materials, a dependence on the Laser Illumination is shown
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field evaporation mechanism of bulk oxides under ultra fast Laser Illumination
Journal of Applied Physics, 2011Co-Authors: A. Vella, Baishakhi Mazumder, G Da Costa, B DeconihoutAbstract:The controlled field evaporation of single atoms from an oxide surface assisted by ultra fast Laser pulses has recently been demonstrated. When UV light is used, a photoionization mechanism was proposed. However, experimental results observed when the Laser intensity and wavelength are changed cannot be explained by this mechanism. Instead, a thermal assisted evaporation mechanism characterized by two evaporation times is proposed. The fast and slow evaporation rates are associated to two cooling processes inside the tip sample. Experiments are carried out on TiO2 and MgO field emitter tips to check the dependence of the evaporation process on structural properties of the oxide. A good agreement between the predictions of our model and the experimental data is found.
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three dimensional thermal response of a metal subwavelength tip under femtosecond Laser Illumination
Physical Review B, 2011Co-Authors: J Houard, F Vurpillot, A. Vella, B DeconihoutAbstract:The current work investigates numerically and experimentally the three-dimensional (3D) thermal response of a subwavelength tip illuminated by an ultrashort Laser pulse. A model is developed on the nanometric scale to predict the 3D tip temperature evolution from the initial Laser irradiation through the thermal equilibrium (several nanoseconds). The evolution of the ion temperature is experimentally monitored by atom probe tomography. The anisotropic ion emission observed on steel specimens illuminated with an ultrashort Laser and the evaporation behavior of amorphous glasses is predicted by our 3D thermal model.
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thermal response of a field emitter subjected to ultra fast Laser Illumination
Journal of Physics D, 2009Co-Authors: F Vurpillot, A. Vella, J Houard, B DeconihoutAbstract:Using an ultra-fast Laser assisted atom probe, the temporal evolution of the temperature of a tungsten field emitter subjected to Illumination is studied. The combination of pump probe experiments and evaporation rate measurements is used to estimate the duration of field evaporation, the induced peak temperature and the cooling time. The main conclusion of the measurements is that, despite a significant heating of the tip by the Laser pulse, the cooling time is anomalously fast, below 0.5 ns. Hence, thermal effects are considered to play a major role in ion emission in contrast to conclusions of our previous works. It is shown that the really fast anomalous cooling rate can only be related to a confined heating zone at the tip apex smaller than the wavelength of the Laser.
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estimation of the cooling times for a metallic tip under Laser Illumination
Applied Physics Letters, 2006Co-Authors: F Vurpillot, Baptiste Gault, A. Vella, M Bouet, B DeconihoutAbstract:The temperature evolution at the apex of a sharply pointed needle submitted to ultrafast pulsed-Laser irradiation was determined using a pump-probe method. The Laser pulse acts as a pump pulse whereas the probe pulse is a fast high-voltage pulse. Then cooling times are consistent with a heating zone of a few microns with a Laser beam polarized along the tip axis and a spot size of 0.8mm.
Hui Cao - One of the best experts on this subject based on the ideXlab platform.
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erratum speckle free Laser imaging using random Laser Illumination
Nature Photonics, 2012Co-Authors: Brandon Redding, Michael A Choma, Hui CaoAbstract:Nature Photon. 6, 355–359; published online 29 April 2012; corrected after print 14 June 2012.). The received date of this Letter was incorrect. This error has been corrected in the HTML and PDF versions of the Letter.
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speckle free Laser imaging using random Laser Illumination
Nature Photonics, 2012Co-Authors: Ando Redding, Michael A Choma, Hui CaoAbstract:Exploiting the low spatial coherence of specifically designed random Lasers, researchers demonstrate speckle-free full-field imaging in the regime of intense optical scattering. Their results show that the quality of images generated from random-Laser Illumination is superior to those generated from spatially coherent Illumination.
Satomi Ohnishi - One of the best experts on this subject based on the ideXlab platform.
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photoinduced alignment of nematic liquid crystal on the polymer surface microrelief
Molecular Crystals and Liquid Crystals, 2001Co-Authors: Alexander V Parfenov, Nobuyuki Tamaoki, Satomi OhnishiAbstract:Polymer film surface modified in the holographic process under the Laser Illumination was used for nematic liquid crystal (LC) alignment. Azobenzene - containing polyurethanes were taken for a mate...
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photoinduced alignment of nematic liquid crystal on the polymer surface microrelief
Journal of Applied Physics, 2000Co-Authors: Alexander V Parfenov, Nobuyuki Tamaoki, Satomi OhnishiAbstract:A polymer film surface modified by Laser Illumination was used as a command surface for nematic liquid crystal (LC). Azobenzene-containing polyurethanes were taken for the material of the film. A relief grating inscribed by Laser Illumination onto the surface of these polymers induced a reorientation of the LC director from the initial homeotropic alignment. Possible applications of the described processes include command-surface creation for liquid-crystal displays, reversible and adaptable liquid-crystal structures for Laser-beam targeting and aiming, etc.
Marcus Alden - One of the best experts on this subject based on the ideXlab platform.
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quantitative imaging of a non combusting diesel spray using structured Laser Illumination planar imaging
Applied Physics B, 2012Co-Authors: Edouard Berrocal, Elias Kristensson, Marcus Alden, P Hottenbach, G GrunefeldAbstract:Due to its transient nature, high atomization process, and rapid generation of fine evaporating droplets, diesel sprays have been, and still remain, one of the most challenging sprays to be fully analyzed and understood by means of non-intrusive diagnostics. The main limitation of Laser techniques for quantitative measurements of diesel sprays concerns the detection of the multiple light scattering resulting from the high optical density of such a scattering medium. A second limitation is the extinction of the incident Laser radiation as it crosses the spray, as well as the attenuation of the signal which is to be detected. All these issues have strongly motivated, during the past decade, the use of X-ray instead of visible light for dense spray diagnostics. However, we demonstrate in this paper that based on an affordable Nd:YAG Laser system, structured Laser Illumination planar imaging (SLIPI) can provide accurate quantitative description of a non-reacting diesel spray injected at 1,100 bar within a room temperature vessel pressurized at 18.6 bar. The technique is used at λ = 355 nm excitation wavelength with 1.0 mol% TMPD dye concentration, for simultaneous LIF/Mie imaging. Furthermore, a novel dual-SLIPI configuration is tested with Mie scattering detection only. The results confirm that a mapping of both the droplet Sauter mean diameter and extinction coefficient can be obtained by such complementary approaches. These new insights are provided in this article at late times after injection start. It is demonstrated that the application of SLIPI to diesel sprays provides valuable quantitative information which was not previously accessible.
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analysis of multiple scattering suppression using structured Laser Illumination planar imaging in scattering and fluorescing media
Optics Express, 2011Co-Authors: Elias Kristensson, Edouard Berrocal, Marcus Alden, L Araneo, J Manin, Mattias Richter, Mark LinneAbstract:The accuracy, precision and limitations of the imaging technique named Structured Laser Illumination Planar Imaging (SLIPI) have been investigated. SLIPI, which allows multiply scattered light to be diminished, has previously demonstrated improvements in image quality and contrast for spray imaging. In the current study the method is applied to a controlled confined environment consisting of a mixture of water and monodisperse polystyrene microspheres. Elastic scattering and fluorescence are studied and the results obtained when probing different particle concentrations and diameters conclusively show the advantages of SLIPI for imaging within moderately turbid media. Although the technique presents both good repeatability and agreement with the Beer-Lambert law, discrepancies in its performance were, however, discovered. Photons undergoing scattering without changing their incident trajectory cannot be discriminated and, owing to differences in scattering phase functions, probing larger particles reduces the suppression of multiply scattered light. However, in terms of visibility such behavior is beneficial as it allows denser media to be probed. It is further demonstrated that the suppression of diffuse light performs equally well regardless of whether photons propagate along the incident direction or towards the camera. In addition, this filtering process acts independently on the spatial distribution of the multiply scattered light but is limited by the finite dynamic range and unavoidable signal noise of the camera.
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extinction coefficient imaging of turbid media using dual structured Laser Illumination planar imaging
Optics Letters, 2011Co-Authors: Elias Kristensson, Edouard Berrocal, Marcus AldenAbstract:We demonstrate a technique, named dual structured Laser Illumination planar imaging (SLIPI), capable of acquiring depth-resolved images of the extinction coefficient. This is achieved by first suppressing the multiply scattered light intensity and then measuring the intensity reduction caused by signal attenuation between two Laser sheets separated by Δz mm. Unlike other methods also able to measure this quantity, the presented approach is based solely on side-scattering detection. The main advantages of dual SLIPI is that it accounts for multiple scattering, provides two-dimensional information, and can be applied on inhomogeneous media.
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high speed structured planar Laser Illumination for contrast improvement of two phase flow images
Optics Letters, 2008Co-Authors: Elias Kristensson, Edouard Berrocal, Mattias Richter, Svengoran Pettersson, Marcus AldenAbstract:A high-speed method to remove blurring effects caused by multiple scattering in planar Laser images of two-phase flows is demonstrated. The technique is based on structured Illumination and is for the first time to our knowledge applied on a dynamic medium. As structured Illumination requires three successive images to be recorded and to freeze the flow motion in time, a high-speed Laser and imaging system is employed. We show that by using a time delay of 55 μs between the images a single-shot representation of a dilute flow of water droplets can be achieved. By having an additional inner stream with known structure and composition, the efficiency of the method is quantitatively evaluated, showing an increase from 58% to 93% in image contrast. Such an improvement allows more accurate analysis and interpretation of scattering two-phase flow images.
