Early Stage Diagnostics for Laser-Induced Aluminum Alloy with Optical Emission Spectroscopy
ZHANG Yong1, XU Tao1, LIU Ying2, DUAN Yi-xiang1*
1. Research Center of Analytical Instrumentation, College of Life Science, Sichuan University, Chengdu 610064, China
2. General Research Institute of Nonferrous Metals, Beijing 100088, China
Abstract：There are many methods to characterize plasma parameters for laser-induced plasma, optical emission spectra method is a very important one to diagnose laser-induced plasma parameters. In this paper, Nd∶YAG solid state laser which output 1 064 nm wavelength interact with aluminum alloy sample, the temporal evolution of spectral line profile, spectral line intensity, continuum intensity, line to background intensity ratio, spectral line broadening and spectral line shift were investigated in detail for laser induced aluminum alloy plasma. The results show that the interaction of electrons between atoms and ions are very intense, which leads to electrons production of laser induced plasma at the early stage. Stark broadening effect of spectra lines are distinct and multiple spectral lines are overlapped. With temporal evolution, the electron density and electron temperature decreased quickly, the multiple spectral lines are separated slowly, and the spectral line profile is becoming thinner and symmetric. For Mg Ⅰ 285.2126 nm characteristic spectral line, the intensity increased with temporal evolution at first, the intensity reached maximum value about 100 ns, and then the intensity decreased with temporal evolution, which is due to the fact that electron and ion are dominated at early stage of laser-induced plasma, atomic spectral line is very weak, with temporal evolution, the process of recombination between electrons dominated and the atomic number density increased, when the atomic number density reached maximum value, the spectral line intensity decreased with temporal evolution because excitation temperature decreased quickly. Taking wavelength in NIST database as reference wavelength, the spectral line shift for MgⅠ 285.212 7 nm and Zn Ⅱ 206.200 4 nm take place red shift at early stage of laser induced plasma, the continuum intensity decreased dramatically by power law with temporal evolution, on the contrary, comparing with continuum intensity and spectral line intensity, continuum intensity attenuate sharply, the line to background intensity ratio increase with temporal evolution. This early phenomenon of laser induced aluminum alloy plasma were discussed in detail from theoretical perspective.
Key words：Laser induced plasma; Spectral line profile; Continuum intensity, Full width at half maximum (FWHM), Spectral line shift
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