The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Leonid V Zhigilei - One of the best experts on this subject based on the ideXlab platform.
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generation of subsurface voids incubation effect and formation of nanoparticles in Short Pulse Laser interactions with bulk metal targets in liquid molecular dynamics study
Journal of Physical Chemistry C, 2017Co-Authors: Chengyu Shih, Maxim V Shugaev, Leonid V ZhigileiAbstract:The ability of Short Pulse Laser ablation in liquids to produce clean colloidal nanoparticles and unusual surface morphology has been employed in a broad range of practical applications. In this paper, we report the results of large-scale molecular dynamics simulations aimed at revealing the key processes that control the surface morphology and nanoparticle size distributions by Pulsed Laser ablation in liquids. The simulations of bulk Ag targets irradiated in water are performed with an advanced computational model combining a coarse-grained representation of liquid environment and an atomistic description of Laser interaction with metal targets. For the irradiation conditions that correspond to the spallation regime in vacuum, the simulations predict that the water environment can prevent the complete separation of the spalled layer from the target, leading to the formation of large subsurface voids stabilized by rapid cooling and solidification. The subsequent irradiation of the Laser-modified surface ...
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atomistic simulation study of Short Pulse Laser interactions with a metal target under conditions of spatial confinement by a transparent overlayer
Journal of Applied Physics, 2014Co-Authors: Eaman T Karim, Robert F Hainsey, Maxim V Shugaev, Chengping Wu, Leonid V ZhigileiAbstract:The distinct characteristics of Short Pulse Laser interactions with a metal target under conditions of spatial confinement by a solid transparent overlayer are investigated in a series of atomistic simulations. The simulations are performed with a computational model combining classical molecular dynamics (MD) technique with a continuum description of the Laser excitation, electron-phonon equilibration, and electronic heat transfer based on two-temperature model (TTM). Two methods for incorporation of the description of a transparent overlayer into the TTM-MD model are designed and parameterized for Ag-silica system. The material response to the Laser energy deposition is studied for a range of Laser fluences that, in the absence of the transparent overlayer, covers the regimes of melting and resolidification, photomechanical spallation, and phase explosion of the overheated surface region. In contrast to the irradiation in vacuum, the spatial confinement by the overlayer facilitates generation of sustain...
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atomistic modeling of Short Pulse Laser ablation of metals connections between melting spallation and phase explosion
Journal of Physical Chemistry C, 2009Co-Authors: Leonid V Zhigilei, Zhibin Lin, D S IvanovAbstract:The mechanisms of Short Pulse Laser interactions with a metal target are investigated in simulations performed with a model combining the molecular dynamics method with a continuum description of Laser excitation, electron−phonon equilibration, and electron heat conduction. Three regimes of material response to Laser irradiation are identified in simulations performed with a 1 ps Laser Pulse, which corresponds to the condition of stress confinement: melting and resolidification of a surface region of the target, photomechanical spallation of a single or multiple layers or droplets, and an explosive disintegration of an overheated surface layer (phase explosion). The processes of Laser melting, spallation, and phase explosion are taking place on the same time scale and are closely intertwined with each other. The transition to the spallation regime results in a reduction of the melting zone and a sharp drop in the duration of the melting and resolidification cycle. The transition from spallation to phase e...
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Numerical modeling of Short Pulse Laser interaction with Au nanoparticle surrounded by water
Applied Surface Science, 2007Co-Authors: Alexey Volkov, Carlos A. Sevilla, Leonid V ZhigileiAbstract:Abstract Short Pulse Laser interaction with a metal nanoparticle surrounded by water is investigated with a hydrodynamic computational model that includes a realistic equation of state for water and accounts for thermoelastic behavior and the kinetics of electron–phonon equilibration in the nanoparticle. Computational results suggest that, at Laser fluences close to the threshold for vapor bubble formation, the region of biological damage due to the Laser-induced thermal spike and the interaction of the pressure wave with internal cell structures can be localized within Short distances from the absorbing particle comparable to the particle diameter. This irradiation regime is suitable for targeted generation of thermal and mechanical damage at the sub-cellular level.
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effect of pressure relaxation on the mechanisms of Short Pulse Laser melting
Physical Review Letters, 2003Co-Authors: D S Ivanov, Leonid V ZhigileiAbstract:The kinetics and microscopic mechanisms of Laser melting of a thin metal film are investigated in a computational study that combines molecular dynamics simulations with a continuum description of the Laser excitation and subsequent relaxation of the conduction band electrons. Two competing melting mechanisms, homogeneous nucleation of liquid regions inside the crystalline material and propagation of melting fronts from external surfaces, are found to be strongly affected by the dynamics of the relaxation of the Laser-induced pressure.
Kunal Mitra - One of the best experts on this subject based on the ideXlab platform.
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tissue response to Short Pulse Laser irradiation
Heat Transfer and Fluid Flow in Biological Processes, 2015Co-Authors: Mohit Ganguly, Ryan Oflaherty, Amir Y Sajjadi, Kunal MitraAbstract:The objective of this chapter is to analyze the transient temperature distribution in skin tissues due to Short Pulse Laser irradiation. COMSOL Multiphysics, a finite element solver, is used to analyze the heat affected zone in a multilayer tissue geometry modeled by considering the embedded vasculature to account for the blood flow. Compared to the existing continuum model, the results predicted by the embedded vasculature simulations are in good agreement with the experimental temperature distribution measurements for experiments on live anesthetized mice. A parametric study has been performed to analyze the effects of varying blood flow velocities on the temperature distribution in tissues. Inclusion of embedded vascularity played a significant role in the analysis of Short Pulse Laser-based therapy of soft tissues.
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bio heat transfer analysis during Short Pulse Laser irradiation of tissues
International Journal of Heat and Mass Transfer, 2008Co-Authors: Megan K Jaunich, Kunal Mitra, Shreya Raje, Kyunghan Kim, Zhixiong GuoAbstract:Abstract The objective of this paper is to analyze the temperature distributions and heat affected zone in skin tissue medium when irradiated with either a collimated or a focused Laser beam from a Short Pulse Laser source. Experiments are performed on multi-layer tissue phantoms simulating skin tissue with embedded inhomogeneities simulating subsurface tumors and as well as on freshly excised mouse skin tissue samples. Two types of Lasers have been used in this study – namely a Q-switched Pulsed 1064 nm Nd:YAG Short Pulse Laser having a Pulse width of 200 ns and a 1552 nm diode Short Pulsed Laser having a Pulse width of 1.3 ps. Experimental measurements of axial and radial temperature distribution in the tissue medium are compared with the numerical modeling results. For numerical modeling, the transient radiative transport equation is first solved using a discrete ordinates method for obtaining the intensity distribution and radiative heat flux inside the tissue medium. Then the temperature distribution is obtained by coupling the bio-heat transfer equation with either hyperbolic non-Fourier or parabolic Fourier heat conduction model. The hyperbolic heat conduction equation is solved using MacCormack’s scheme with error terms correction. It is observed that experimentally measured temperature distribution is in good agreement with that predicted by hyperbolic heat conduction model. The experimental measurements demonstrate that converging Laser beam focused directly at the subsurface location can produce desired high temperature at that location compared to that produced by collimated Laser beam for the same Laser parameters. Finally the ablated tissue removal is characterized using histological studies as a function of Laser parameters.
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time resolved optical tomography using Short Pulse Laser for tumor detection
Applied Optics, 2006Co-Authors: Soumyadipta Basu, Kunal Mitra, Tuan VodinhAbstract:Our objective is to perform a comprehensive experimental and numerical analysis of the Short-Pulse Laser interaction with a tissue medium with the goal of tumor-cancer diagnostics. For a Short-Pulse Laser source, the shape of the output signal is a function of the optical properties of the medium, and hence the scattered temporal optical signal helps in understanding the medium characteristics. Initially experiments are performed on tissue phantoms embedded with inhomogeneities to optimize the time-resolved optical detection scheme. Both the temporal and the spatial profiles of the scattered reflected and transmitted optical signals are compared with the numerical modeling results obtained by solving the transient radiative transport equation using the discrete ordinates technique. Next experiments are performed on in vitro rat tissue samples to characterize the interaction of light with skin layers and to validate the time-varying optical signatures with the numerical model. The numerical modeling results and the experimental measurements are in excellent agreement for the different parameters studied. The final step is to perform in vivo imaging of anesthetized rats with tumor-promoting agents injected inside skin tissues and of an anesthetized mouse with mammary tumors to demonstrate the feasibility of the technique for detecting tumors in an animal model.
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development and comparison of the dtm the dom and the fvm formulations for the Short Pulse Laser transport through a participating medium
International Journal of Heat and Mass Transfer, 2006Co-Authors: Subhash C Mishra, Pranshu Chugh, Pranav Kumar, Kunal MitraAbstract:The present article deals with the analysis of transient radiative transfer caused by a Short-Pulse Laser irradiation on a participating medium. A general formulation of the governing transient radiative transfer equation applicable to a 3-D Cartesian enclosure has been presented. To solve the transient radiative transfer equation, formulations have been presented for the three commonly used methods in the study of radiative heat transfer, viz., the discrete transfer method, the discrete ordinate method and the finite volume method. To show the uniformity in the formulations in the three methods, the intensity directions and the angular quadrature schemes for computing the incident radiation and heat flux have been taken the same. To validate the formulations and to compare the performance of the three methods, effect of a square Short-Pulse Laser having Pulse-width of the order of a femtosecond on transmittance and reflectance signals in case of an absorbing and scattering planar layer has been studied. Effects of the medium properties such as the extinction coefficient, the scattering albedo and the anisotropy factor and the Laser properties such as the Pulse-width and the angle of incidence on the transmittance and the reflectance signals have been compared. In all the cases, results of the three methods were found to compare very well with each other. Computationally, the discrete ordinate method was found to be the most efficient.
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temporal analysis of reflected optical signals for Short Pulse Laser interaction with nonhomogeneous tissue phantoms
Journal of Quantitative Spectroscopy & Radiative Transfer, 2005Co-Authors: Ashish Trivedi, Soumyadipta Basu, Kunal MitraAbstract:Abstract The use of Short Pulse Laser for minimally invasive detection scheme has become an indispensable tool in the technological arsenal of modern medicine and biomedical engineering. In this work, a time-resolved technique has been used to detect tumors/inhomogeneities in tissues by measuring transmitted and reflected scattered temporal optical signals when a Short Pulse Laser source is incident on tissue phantoms. A parametric study involving different scattering and absorption coefficients of tissue phantoms and inhomogeneities, size of inhomogeneity as well as the detector position is performed. The experimental measurements are validated with a numerical solution of the transient radiative transport equation obtained by using discrete ordinates method. Thus, both simultaneous experimental and numerical studies are critical for predicting the optical properties of tissues and inhomogeneities from temporal scattered optical signal measurements.
D S Ivanov - One of the best experts on this subject based on the ideXlab platform.
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atomistic modeling of Short Pulse Laser ablation of metals connections between melting spallation and phase explosion
Journal of Physical Chemistry C, 2009Co-Authors: Leonid V Zhigilei, Zhibin Lin, D S IvanovAbstract:The mechanisms of Short Pulse Laser interactions with a metal target are investigated in simulations performed with a model combining the molecular dynamics method with a continuum description of Laser excitation, electron−phonon equilibration, and electron heat conduction. Three regimes of material response to Laser irradiation are identified in simulations performed with a 1 ps Laser Pulse, which corresponds to the condition of stress confinement: melting and resolidification of a surface region of the target, photomechanical spallation of a single or multiple layers or droplets, and an explosive disintegration of an overheated surface layer (phase explosion). The processes of Laser melting, spallation, and phase explosion are taking place on the same time scale and are closely intertwined with each other. The transition to the spallation regime results in a reduction of the melting zone and a sharp drop in the duration of the melting and resolidification cycle. The transition from spallation to phase e...
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effect of pressure relaxation on the mechanisms of Short Pulse Laser melting
Physical Review Letters, 2003Co-Authors: D S Ivanov, Leonid V ZhigileiAbstract:The kinetics and microscopic mechanisms of Laser melting of a thin metal film are investigated in a computational study that combines molecular dynamics simulations with a continuum description of the Laser excitation and subsequent relaxation of the conduction band electrons. Two competing melting mechanisms, homogeneous nucleation of liquid regions inside the crystalline material and propagation of melting fronts from external surfaces, are found to be strongly affected by the dynamics of the relaxation of the Laser-induced pressure.
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combined atomistic continuum modeling of Short Pulse Laser melting and disintegration of metal films
Physical Review B, 2003Co-Authors: D S Ivanov, Leonid V ZhigileiAbstract:The kinetics and microscopic mechanisms of Laser melting and disintegration of thin Ni and Au films irradiated by a Short, from 200 fs to 150 ps, Laser Pulse are investigated in a coupled atomistic-continuum computational model. The model provides a detailed atomic-level description of fast nonequilibrium processes of Laser melting and film disintegration and, at the same time, ensures an adequate description of the Laser light absorption by the conduction band electrons, the energy transfer to the lattice due to the electron-phonon coupling, and the fast electron heat conduction in metals. The interplay of two competing processes, the propagation of the liquid-crystal interfaces (melting fronts) from the external surfaces of the film and homogeneous nucleation and growth of liquid regions inside the crystal, is found to be responsible for melting of metal films irradiated by Laser Pulses at fluences close to the melting threshold. The relative contributions of the homogeneous and heterogeneous melting mechanisms are defined by the Laser fluence, Pulse duration, and the strength of the electron-phonon coupling. At high Laser fluences, significantly exceeding the threshold for the melting onset, a collapse of the crystal structure overheated above the limit of crystal stability takes place simultaneously in the whole overheated region within \ensuremath{\sim}2 ps, skipping the intermediate liquid-crystal coexistence stage. Under conditions of the inertial stress confinement, realized in the case of Short $\ensuremath{\tau}l~10\mathrm{ps}$ Laser Pulses and strong electron-phonon coupling (Ni films), the dynamics of the relaxation of the Laser-induced pressure has a profound effect on the temperature distribution in the irradiated films as well as on both homogeneous and heterogeneous melting processes. Anisotropic lattice distortions and stress gradients associated with the relaxation of the Laser-induced pressure destabilize the crystal lattice, reduce the overheating required for the initiation of homogeneous melting down to $T\ensuremath{\approx}{1.05T}_{m},$ and expand the range of Pulse durations for which homogeneous melting is observed in 50 nm Ni films up to \ensuremath{\sim}150 ps. High tensile stresses generated in the middle of an irradiated film can also lead to the mechanical disintegration of the film.
S.n. Chen - One of the best experts on this subject based on the ideXlab platform.
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first demonstration of multi mev proton acceleration from a cryogenic hydrogen ribbon target
Plasma Physics and Controlled Fusion, 2018Co-Authors: S D Kraft, Josefine Metzkesng, Hans-peter Schlenvoigt, K Zeil, Sylvain Michaux, L. Obst, J.-p. Périn, Denis Chatain, S.n. ChenAbstract:We show efficient Laser driven proton acceleration up to 14 MeV from a 62 μm thick cryogenic hydrogen ribbon. Pulses of the Short Pulse Laser ELFIE at LULI with a Pulse length of ≈350 fs at an energy of 8 J per Pulse are directed onto the target. The results are compared to proton spectra from metal and plastic foils with different thicknesses and show a similarly good performance both in maximum energy as well as in proton number. Thus, this target type is a promising candidate for experiments with high repetition rate Laser systems.
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experimental evidence for Short Pulse Laser heating of solid density target to high bulk temperatures
Scientific Reports, 2017Co-Authors: A A Soloviev, S.n. Chen, K F Burdonov, A Eremeev, A V Korzhimanov, G V Pokrovskiy, T A Pikuz, G RevetAbstract:Heating efficiently solid-density, or even compressed, matter has been a long-sought goal in order to allow investigation of the properties of such state of matter of interest for various domains, e.g. astrophysics. High-power Lasers, pinches, and more recently Free-Electron-Lasers (FELs) have been used in this respect. Here we show that by using the high-power, high-contrast “PEARL” Laser (Institute of Applied Physics-Russian Academy of Science, Nizhny Novgorod, Russia) delivering 7.5 J in a 60 fs Laser Pulse, such coupling can be efficiently obtained, resulting in heating of a slab of solid-density Al of 0.8 µm thickness at a temperature of 300 eV, and with minimal density gradients. The characterization of the target heating is achieved combining X-ray spectrometry and measurement of the protons accelerated from the Al slab. The measured heating conditions are consistent with a three-temperatures model that simulates resistive and collisional heating of the bulk induced by the hot electrons. Such effective Laser energy deposition is achieved owing to the intrinsic high contrast of the Laser which results from the Optical Parametric Chirped Pulse Amplification technology it is based on, allowing to attain high target temperatures in a very compact manner, e.g. in comparison with large-scale FEL facilities.
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monochromatic Short Pulse Laser produced ion beam using a compact passive magnetic device
Review of Scientific Instruments, 2014Co-Authors: S.n. Chen, M Gauthier, D P Higginson, S Dorard, F Mangia, R Riquier, S Atzeni, J R Marques, J FuchsAbstract:High-intensity Laser accelerated protons and ions are emerging sources with complementary characteristics to those of conventional sources, namely high charge, high current, and Short bunch duration, and therefore can be useful for dedicated applications. However, these beams exhibit a broadband energy spectrum when, for some experiments, monoenergetic beams are required. We present here an adaptation of conventional chicane devices in a compact form (10 cm × 20 cm) which enables selection of a specific energy interval from the broadband spectrum. This is achieved by employing magnetic fields to bend the trajectory of the Laser produced proton beam through two slits in order to select the minimum and maximum beam energy. The device enables a production of a high current, Short duration source with a reproducible output spectrum from Short Pulse Laser produced charged particle beams.
Subhash C Mishra - One of the best experts on this subject based on the ideXlab platform.
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radiative transfer of a Short Pulse Laser wave of gaussian temporal profile through a two dimensional participating medium containing inhomogeneities of different shapes at various locations
Numerical Heat Transfer Part A-applications, 2008Co-Authors: R Muthukumaran, Subhash C MishraAbstract:The effects of the propagation of a Short-Pulse Laser wave of Gaussian temporal profile through a two-dimensional rectangular participating medium containing inhomogeneities of different shapes placed at various positions are discussed with in this article. The containing medium and its inhomogeneities differ by their scattering albedos. The thermal signatures at the boundaries are investigated for the effects of the extinction coefficient and for the shapes and locations of inhomogeneities. Heat flux distributions within the medium are also studied. Numerical information about spatial and temporal distributions of heat fluxes inside the medium are used to confirm the qualitative nature of the medium. The finite-volume method is used to solve the problem.
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interaction of a Short Pulse Laser of a gaussian temporal profile with an inhomogeneous medium
Numerical Heat Transfer Part A-applications, 2007Co-Authors: R Muthukumaran, Subhash C MishraAbstract:Transport of a Short-Pulse Laser in an inhomogeneous planar participating medium is investigated. The Pulse is a Gaussian function in time. Discrete as well as continuous variations in the scattering albedo across the layers are considered to be the cause of inhomogeneties in the absorbing-scattering medium. Optical depths of different layers too are considered different. The finite volume method is used to analyze the problem. Transmittance and reflectance signals are studied for different situations. Characteristic signals are obtained for specific inhomogeneties in the medium.
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development and comparison of the dtm the dom and the fvm formulations for the Short Pulse Laser transport through a participating medium
International Journal of Heat and Mass Transfer, 2006Co-Authors: Subhash C Mishra, Pranshu Chugh, Pranav Kumar, Kunal MitraAbstract:The present article deals with the analysis of transient radiative transfer caused by a Short-Pulse Laser irradiation on a participating medium. A general formulation of the governing transient radiative transfer equation applicable to a 3-D Cartesian enclosure has been presented. To solve the transient radiative transfer equation, formulations have been presented for the three commonly used methods in the study of radiative heat transfer, viz., the discrete transfer method, the discrete ordinate method and the finite volume method. To show the uniformity in the formulations in the three methods, the intensity directions and the angular quadrature schemes for computing the incident radiation and heat flux have been taken the same. To validate the formulations and to compare the performance of the three methods, effect of a square Short-Pulse Laser having Pulse-width of the order of a femtosecond on transmittance and reflectance signals in case of an absorbing and scattering planar layer has been studied. Effects of the medium properties such as the extinction coefficient, the scattering albedo and the anisotropy factor and the Laser properties such as the Pulse-width and the angle of incidence on the transmittance and the reflectance signals have been compared. In all the cases, results of the three methods were found to compare very well with each other. Computationally, the discrete ordinate method was found to be the most efficient.
