Multistage plasma initiation process by pulsed CO2laser irradiation of a Ti sample in an ambient gas (He, Ar, or N2)
作者:
J. Hermann,
C. Boulmer‐Leborgne,
I. N. Mihailescu,
B. Dubreuil,
期刊:
Journal of Applied Physics
(AIP Available online 1993)
卷期:
Volume 73,
issue 3
页码: 1091-1099
ISSN:0021-8979
年代: 1993
DOI:10.1063/1.353271
出版商: AIP
数据来源: AIP
摘要:
New experimental results are reported on plasma initiation in front of a titanium sample irradiated by ir (&lgr;=10.6 &mgr;m) laser pulses in an ambient gas (He, Ar, and N2) at pressures ranging from several Torr up to the atmosphere. The plasma is studied by space‐ and time‐resolved emission spectroscopy, while sample vaporization is probed by laser‐induced fluorescence spectroscopy. Threshold laser intensities leading to the formation of a plasma in the vapor and in the ambient gases are determined. Experimental results support the model of a vaporization mechanism for the plasma initiation (vaporization‐initiated plasma breakdown). The plasma initiation is described by simple numerical criteria based on a two‐stage process. Theoretical predictions are found to be in a reasonable agreement with the experiment. This study provides also a clear explanation of the influence of the ambient gas on the laser beam‐metal surface energy transfer. Laser irradiation always causes an important vaporization when performed in He, while in the case of Ar or N2, the interaction is reduced in heating and vaporization of some surface defects and impurities.
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