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Title: Laser ablation induced vapor plume expansion into a background gas. II. Experimental analysis

Abstract

Laser ablation of copper with a 4 ns laser pulse at 1064 nm was studied with a series of synchronized shadowgraph (100 fs laser pulses at 400 nm) and emission images (spectral line at 515 nm). Data were obtained at two laser pulse energies (10 and 30 mJ) and in three background gases (He, Ne, and Ar) at atmospheric pressure. The laser energy conversion ratio and the amount of sample vaporized for ablation in each condition were obtained by the theoretical analysis reported in paper I from trajectories of the external shock wave, internal shock wave, and contact surface between the Cu vapor and the background gas. All three quantities were measured from shadowgraph and emission images. The results showed that E, the amount of energy that is absorbed by the copper vapor, decreases as the atomic mass of the background gas increases; and M, the mass of the sample converted into vapor, is almost independent of the background gas [Horn et al., Appl. Surf. Sci. 182, 91 (2001)]. A physical interpretation is given based on the phenomena observed in shadowgraph and emission images during the first tens of nanoseconds after the beginning of the laser pulse for ablation inmore » different background gases. In addition, an internal shock wave was observed in the emission images during the first tens of nanoseconds after the laser pulse, which strikes the surface and should be one of the mechanisms inducing the liquid sample ejection. Also, a significant vortex ring near the target was observed in emission images at longer times after the laser pulse (>100 ns) which distorts the otherwise hemispherical expansion of the vapor plume.« less

Authors:
; ; ;  [1];  [2];  [2]
  1. Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20982623
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 2; Other Information: DOI: 10.1063/1.2431085; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 36 MATERIALS SCIENCE; ABLATION; ARGON; ATMOSPHERIC PRESSURE; COPPER; ENERGY CONVERSION; EXPANSION; HELIUM; LASERS; LIGHT TRANSMISSION; NEON; PLASMA; PLASMA DIAGNOSTICS; PLUMES; PULSES; SHOCK WAVES; TRAJECTORIES; VAPORS; WALL EFFECTS

Citation Formats

Wen, Sy-Bor, Mao, Xianglei, Greif, Ralph, Russo, Richard E., Department of Mechanical Engineering, University of California, Berkeley, California 94720, and Lawrence Berkeley National Laboratory, Berkeley, California 94720. Laser ablation induced vapor plume expansion into a background gas. II. Experimental analysis. United States: N. p., 2007. Web. doi:10.1063/1.2431085.
Wen, Sy-Bor, Mao, Xianglei, Greif, Ralph, Russo, Richard E., Department of Mechanical Engineering, University of California, Berkeley, California 94720, & Lawrence Berkeley National Laboratory, Berkeley, California 94720. Laser ablation induced vapor plume expansion into a background gas. II. Experimental analysis. United States. doi:10.1063/1.2431085.
Wen, Sy-Bor, Mao, Xianglei, Greif, Ralph, Russo, Richard E., Department of Mechanical Engineering, University of California, Berkeley, California 94720, and Lawrence Berkeley National Laboratory, Berkeley, California 94720. Mon . "Laser ablation induced vapor plume expansion into a background gas. II. Experimental analysis". United States. doi:10.1063/1.2431085.
@article{osti_20982623,
title = {Laser ablation induced vapor plume expansion into a background gas. II. Experimental analysis},
author = {Wen, Sy-Bor and Mao, Xianglei and Greif, Ralph and Russo, Richard E. and Department of Mechanical Engineering, University of California, Berkeley, California 94720 and Lawrence Berkeley National Laboratory, Berkeley, California 94720},
abstractNote = {Laser ablation of copper with a 4 ns laser pulse at 1064 nm was studied with a series of synchronized shadowgraph (100 fs laser pulses at 400 nm) and emission images (spectral line at 515 nm). Data were obtained at two laser pulse energies (10 and 30 mJ) and in three background gases (He, Ne, and Ar) at atmospheric pressure. The laser energy conversion ratio and the amount of sample vaporized for ablation in each condition were obtained by the theoretical analysis reported in paper I from trajectories of the external shock wave, internal shock wave, and contact surface between the Cu vapor and the background gas. All three quantities were measured from shadowgraph and emission images. The results showed that E, the amount of energy that is absorbed by the copper vapor, decreases as the atomic mass of the background gas increases; and M, the mass of the sample converted into vapor, is almost independent of the background gas [Horn et al., Appl. Surf. Sci. 182, 91 (2001)]. A physical interpretation is given based on the phenomena observed in shadowgraph and emission images during the first tens of nanoseconds after the beginning of the laser pulse for ablation in different background gases. In addition, an internal shock wave was observed in the emission images during the first tens of nanoseconds after the laser pulse, which strikes the surface and should be one of the mechanisms inducing the liquid sample ejection. Also, a significant vortex ring near the target was observed in emission images at longer times after the laser pulse (>100 ns) which distorts the otherwise hemispherical expansion of the vapor plume.},
doi = {10.1063/1.2431085},
journal = {Journal of Applied Physics},
number = 2,
volume = 101,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • A study of the gas dynamics of the vapor plume generated during laser ablation was conducted including a counterpropagating internal shock wave. The density, pressure, and temperature distributions between the external shock wave front and the sample surface were determined by solving the integrated conservation equations of mass, momentum, and energy. The positions of the shock waves and the contact surface (boundary that separates the compressed ambient gas and the vapor plume) were obtained when the incident laser energy that is transferred to the vapor plume and to the background gas, E, and the vaporized sample mass, M, are specified.more » The values for E and M were obtained from a comparison of the calculated trajectories of the external shock wave and the contact surface with experimental results for a copper sample under different laser fluences. Thus E and M, which are the two dominant parameters for laser ablation and which cannot be measured directly, can be determined. In addition, the internal shock wave propagation within the vapor plume was determined; the interaction of the internal shock wave with the sample may be one of the mechanisms inducing liquid sample ejection during laser ablation.« less
  • No abstract prepared.
  • A study of the gas dynamics of the vapor plume generatedduring laser ablation was conducted including a counterpropagatinginternal shock wave. The density, pressure, and temperature distributionsbetween the external shock wave front and the sample surface weredetermined by solving the integrated conservation equations of mass,momentum, and energy. The positions of the shock waves and the contactsurface (boundary that separates the compressed ambient gas and the vaporplume) were obtained when the incident laser energy that is transferredto the vapor plume and to the background gas, E, and the vaporized samplemass, M, are specified. The values for E and M were obtained frommore » acomparison of the calculated trajectories of the external shock wave andthe contact surface with experimental results for a copper sample underdifferent laser fluences. Thus E and M, which are the two dominantparameters for laser ablation and which cannot be measured directly, canbe determined. In addition, the internal shock wave propagation withinthe vapor plume was determined; the interaction of the internal shockwave with the sample may be one of the mechanisms inducing liquid sampleejection during laser ablation. (c) 2007 American Institute ofPhysics.« less
  • A one-dimensional gas-dynamic model is presented for the laser ablation of Cu and the expansion of the Cu vapor in a background gas (He) at 1 atm. The ionization of Cu and He, the inverse bremsstrahlung absorption processes and photoionization process, and the back flux onto the target are considered simultaneously. The binary diffusion, the viscosity, and the thermal conduction including the electron thermal conduction are considered as well. Numerical results show that the consideration of ionization and laser absorption in the plume greatly influences the gas dynamics. The ionization of Cu enables the recondensation at the target surface tomore » happen even during the laser pulse. The ionization degree of Cu and He may change greatly with the location in the plume. For laser irradiances ranging from 2 to 9x10{sup 12} W/m{sup 2}, the simulations show that the second-order ionization of Cu competes with the first-order ionization. In the region close to the target surface, the first-order ionization of Cu dominates. In the core of the plasma, the second-order ionization of Cu may dominate over the first-order ionization at laser irradiances higher than 7x10{sup 12} W/m{sup 2}. In the mixing layer, the first-order ionization of Cu is always more important than the second-order ionization although the latter increases monotonously with laser irradiance. The ionization of He is only important in the mixing layer. The plume expansion velocity is much larger than that without ionization and laser absorption by the plume. The relative importance of different laser absorption mechanisms may change with time. Close to the surface photoionization and electron-neutral inverse bremsstrahlung are always important. Once the ionization in the plume starts, at later time, electron-ion inverse bremsstrahlung can become more important than photoionization in the plume core until the shock wave front. Unlike in the vacuum case, electron-neutral inverse bremsstrahlung is very strong due to the relatively high number density of neutral atoms in the plume in the presence of a dense ambient gas. A similar laser irradiance threshold is found for the ablation rate and the plasma formation in the plume, which agrees well with the case of nanosecond laser ablation of metals in vacuum.« less
  • Laser-induced plasma from an aluminum target in one-atmosphere argon background has been investigated with ablation using nanosecond ultraviolet (UV: 355 nm) or infrared (IR: 1064 nm) laser pulses. Time- and space-resolved emission spectroscopy was used as a diagnostics tool to have access to the plasma parameters during its propagation into the background, such as optical emission intensity, electron density, and temperature. The specific feature of nanosecond laser ablation is that the pulse duration is significantly longer than the initiation time of the plasma. Laser-supported absorption wave due to post-ablation absorption of the laser radiation by the vapor plume and themore » shocked background gas plays a dominant role in the propagation and subsequently the behavior of the plasma. We demonstrate that the difference in absorption rate between UV and IR radiations leads to different propagation behaviors of the plasma produced with these radiations. The consequence is that higher electron density and temperature are observed for UV ablation. While for IR ablation, the plasma is found with lower electron density and temperature in a larger and more homogenous axial profile. The difference is also that for UV ablation, the background gas is principally evacuated by the expansion of the vapor plume as predicted by the standard piston model. While for IR ablation, the background gas is effectively mixed to the ejected vapor at least hundreds of nanoseconds after the initiation of the plasma. Our observations suggest a description by laser-supported combustion wave for the propagation of the plasma produced by UV laser, while that by laser-supported detonation wave for the propagation of the plasma produced by IR laser. Finally, practical consequences of specific expansion behavior for UV or IR ablation are discussed in terms of analytical performance promised by corresponding plasmas for application with laser-induced breakdown spectroscopy.« less