Laser-Induced Breakdown of Metal Vapor

Mazhukin, V. I.; Gusev, I.V.; Smurov, I.; Flamant, Gilles

doi:10.1006/mchj.1994.1104

Cited by 11 publications

(6 citation statements)

References 2 publications

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“…Different species of atoms (nitrogen atoms for the ambient gas and material atoms in the material vapour) are taken into account to calculate the degree of ionization in the different regions of the interaction zone by the Saha equation [25]. This approach seems to be justified because, as shown in [26], the electron density calculated with the Saha equation using the gas temperatures is comparable with the results of a collisionradiation model describing the kinetics of non-equilibrium ionization and recombination at the same temperature value for the ions. The results of the modelling for copper as target material showed that the transient power evolution of the undisturbed laser pulse is nearly the same as that with consideration of inverse Bremsstrahlung.…”

Section: 31mentioning

confidence: 99%

Investigations of extinction coefficients during excimer laser ablation and their interpretation in terms of Rayleigh scattering

Schittenhelm

Callies

Berger

et al. 1996

J. Phys. D: Appl. Phys.

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KrF excimer laser ablation in air at an ambient pressure of 1 bar leads to an intense evaporation of target material. The ablated material compresses the surrounding gas and leads to the formation of a shock wave. The incident laser radiation interacts with the compressed, ionized ambient gas behind the shock front and the partially ionized material vapour. This interaction is responsible for extinction of the incident laser radiation and exerts effects on the processing result and the efficiency of the treatment. The transmission of the incident laser power through the laser-induced interaction zone was measured using a target foil prepared with a small aperture within the area of irradiation. Extinction coefficients in the range were measured for PET, copper and aluminium. In order to explain the experimental results, a theoretical study of possible extinction mechanisms was performed on the basis of inverse Bremsstrahlung theory and scattering theories. The thermodynamic properties in the interaction zone were calculated by using a shock wave theory. Under the assumption that this theory describes the thermodynamic properties in a physically correct manner, it will be shown that inverse Bremsstrahlung cannot explain the measured small degrees of transmission. Interactions between the incident laser light and material clusters in the laser-induced material vapour, like Rayleigh scattering, however, can lead to values comparable to the experimental findings. In order to classify the scattered fraction from the incident laser power, information on the size of the scattering particles is necessary. Therefore, a simplified model of cluster condensation in the material vapour and the scattering of incident laser power by these clusters was developed. Theoretically obtained results on this basis will be compared with the experimental data.

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Section: 31mentioning

confidence: 99%

Investigations of extinction coefficients during excimer laser ablation and their interpretation in terms of Rayleigh scattering

Schittenhelm

Callies

Berger

et al. 1996

J. Phys. D: Appl. Phys.

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“…At the moment of optical breakdown, the collision frequencies are approximately equal v en Ϸv ei . 5,23 The dynamics of the process depends on both the characteristics of the evaporated material ͑its temperature, density, electron configuration, transition energy, and the ionization potential of atoms͒ and the laser action mode ͑the intensity, the wavelength, the duration, and the pulse temporal shape͒.…”

Section: Statement Of the Problemmentioning

confidence: 99%

“…Mathematical models describing the level-by-level kinetics, photoprocesses and ionization-recombination processes are based on the electron configuration of atoms and ions under study. 5 Considerations of the threshold conditions of plasma formation showed that the characteristic temperature of the electron gas does not usually exceed a few electron volts. Therefore it is sufficient to restrict a mathematical description of optical breakdown by the account of kinetic processes for the case of a neutral atom with the ionization potential J 0 ϭ5.986 eV.…”

Section: A Transient Collision-radiation Modelmentioning

confidence: 99%

“…To describe this process, it is sufficient to apply the appropriate kinetic collision-radiation model supplemented by the energy balance equations. 5,6 In a medium, that is ini-tially at rest, the radiation transfer and the macroscopic movement of vapor start much later, when the system approaches the state of local thermodynamic equilibrium, therefore, at the initial stage of breakdown they can be neglected. Thus, mathematical formulation of the problem gets simpler, while the threshold conditions of plasma formation and its characteristic duration can be determined with sufficient accuracy.…”

Section: Introductionmentioning

confidence: 99%

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Optical breakdown in aluminum vapor induced by ultraviolet laser radiation

Mazhukin¹,

Nossov²,

Nickiforov³

et al. 2003

Journal of Applied Physics

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Theoretical analysis of the evolution of nonequilibrium plasma induced by ultraviolet laser radiation is carried out. Intensity threshold values are studied by mathematical modeling as a function of laser-pulse wavelength. Basic mechanisms of nonequilibrium ionization of aluminum vapor are analyzed and the dominant role of photo-processes, namely, resonant and nonresonant photoexcitation and photoionization, is shown. The modeling results are in good agreement with experimental data on optical breakdown in aluminum vapor by the excimer laser radiation in nanosecond and microsecond range.

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“…1% ionization in one atmosphere pressure at the end of the laser pulse. The threshold may also be defined in term of ionization frequency (ν i > 10 14 s −1 ) or by the preponderance of the very efficient electron energy gain process: electron/ion IBE [27].…”

Section: Metallic Vapour Statementioning

confidence: 99%

A contribution to the understanding of the plasma ignition mechanism above a metal target under UV laser irradiation

Thomann

Boulmer‐Leborgne

Dubreuil

1997

Plasma Sources Sci. Technol.

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In this paper, the plasma ignition process above a metallic surface submitted to UV laser irradiation is studied. An easy model based on the hypothesis of thermal equilibrium between ejected vapour and heated surface, and of a local thermodynamic equilibrium state of the vapour, is used to characterize the metallic vapour at the end of the laser pulse. Then the efficiency of the different elementary mechanisms liable to sustain or to prevent the ionization process in this medium is discussed depending on the laser power density. In this work, the calculations are applied to the case of the interaction between an excimer XeCl laser beam (λ = 308 nm, τ 1 = 28 ns) and titanium target. It is shown that the thermal heated metallic vapour is partially ionized and contains excited and singly ionized species at high densities (10 19 -10 20 atoms cm −2 ). The electron temperature in this medium is found to be around 1 eV. The study of the ionization rise in the vapour evidences the important role played by the single-photon ionization process and the electron/ion inverse bremsstrahlung effect. For laser power densities above 100 MW cm −2 (laser fluence of 2 J cm −2 ), the ionization level is found to increase before the laser pulse end, and a thermal evaporation regime is reached. As the laser power density exceeds 500 MW cm −2 (fluence of 10 J cm −2 ), an avalanche breakdown is liable to occur in the vapour before the pulse end and the plasma governs the evaporation mode. The results presented here are in good agreement with experimental observations and with results from more complex models reported in the literature.

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Laser-Induced Breakdown of Metal Vapor

Cited by 11 publications

References 2 publications

Investigations of extinction coefficients during excimer laser ablation and their interpretation in terms of Rayleigh scattering

Investigations of extinction coefficients during excimer laser ablation and their interpretation in terms of Rayleigh scattering

Optical breakdown in aluminum vapor induced by ultraviolet laser radiation

A contribution to the understanding of the plasma ignition mechanism above a metal target under UV laser irradiation

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