Insights in the laser-induced breakdown spectroscopy signal generation underwater using dual pulse excitation — Part I: Vapor bubble,shockwaves and plasma |
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| Institution: | 1. ENEA (UTAPRAD-DIM), Via. E. Fermi 45, 00044 Frascati (RM), Italy;2. Dept. of Analytical Chemistry, Faculty of Sciences, University of Málaga, Málaga, Spain;3. Institute of Physics, University of Belgrade, Belgrade, Serbia;1. Embrapa Instrumentation, P.O. Box 741, 13561-206 São Carlos, SP, Brazil.;2. CNR, Istituto di Nanotecnologia (NANOTEC) – PLasMI Lab, Bari, 70126 Bari, Italy;3. Instituto de Física, Universidade Federal do Mato Grosso do Sul, P.O. Box 549, 79070-900 Campo Grande, MS, Brazil;4. Embrapa Solos, Rua Jardim Botânico 1024, 22460-000 Rio de Janeiro, RJ, Brazil;5. Embrapa Pecuária Sudeste, P.O. Box 741, 13560-970 São Carlos, SP, Brazil;1. National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, PA 15236, USA;2. Department of Physics and Astronomy, Mississippi State University, Mississippi State, MS 39762, USA;3. National Energy Technology Laboratory, AECOM Technology Corporation, Pittsburgh, PA 15236, USA;1. School of Mechanical Engineering, Xi''an Jiaotong University, Xi''an 710049, China;2. Graduate School of Advanced Technology and Science, Tokushima University, Tokushima 770-8501, Japan;3. State Key Laboratory of Multiphase Flow in Power Engineering, Xi''an Jiaotong University, Xi''an 710049, China;4. Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan;1. ENEA (UTAPRAD-DIM), Via. E. Fermi 45, 00044 Frascati (RM), Italy;2. Institute of Physics, University of Belgrade, 11080 Belgrade, Serbia |
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| Abstract: | Plasma and vapor bubble formation and evolution after a nanosecond laser pulse delivered to aluminum targets inside water were studied by fast photography. This technique was also applied to monitor the plasma produced by a second laser pulse and for different interpulse delays. The bubble growth was evident only after 3 μs from the first laser pulse and the bubble shape changed during expansion and collapse cycles. The evolution and propagation of the initial shockwave and its reflections both from the back sample surface and cell walls were detected by Schlieren photography. The primary plasma develops in two phases: violent particle expulsion and ionization during the first μs, followed by slow plasma growth from the ablation crater into the evolving vapor bubble. The shape of the secondary plasma strongly depends on the inner bubble pressure whereas the particle expulsion into the expanded bubble is much less evident. Both the primary and secondary plasma have similar duration of about 30 μs. Detection efficiency of the secondary plasma is much reduced by light refraction at the curved bubble–water interface, which behaves as a negative lens; this leads to an apparent reduction of the plasma dimensions. Defocusing power of the bubble lens increases with its expansion due to the lowering of the vapor's refraction index with respect to that of the surrounding liquid (Lazic et al., 2012 1]). Smell's reflections of secondary plasma radiation at the expanded bubble wall redistribute the detected intensity on a wavelength-dependent way and allow gathering of the emission also from the external plasma layer that otherwise, would not enter into the optical system. |
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