Study Of Spectral Characteritcs Of Laser-Induced Metal Plasma

In this paper, the pectral characteristics of laser-induced metal plasma were studied. The laser spectrum analytical system is composed of a high-energy neodymium glass laser (0～25J), a multifunctional and automatic scanning spectrometer, a CCD detector, a delay system, and a computer. National standard metal samples were used as the ablation samples. The main subjects are as the following:1. Enhancement of the prefabricated keyhole on the radiation of laser-induced stainless steel plasmasThe effects of different sizes of prefabricated keyhole on the radiation characteristic of laser-induced stainless steel plasma have been investigated. The study results showed that, when a laser beam acted on the surface of the stainless steel sample with prefabricated keyholes(d=1.5mm, h=0.8mm), the spectral intensity and signal-to-background ratio of laser plasma increased in the range of 71.5%～125.8% and 7.6%～18.5%; while the plasma temperature and electron density increased about 1200K and 1.21×1016cm-3, respectively. This proved that the suitable size of prefabricated keyhole had a significant enhancement effect on the radiation of laser-induced stainless steel plasma.2. Enhancement effect of argon atmosphere at high pressure on radiation of laser plasmasIn this experiment, the enhancement effect of Ar atmosphere at high-pressure (0.0-0.5MPa) on emission spectrum of nickel-chrome-molybdenum-vanadium-itanium steel sample was studied. The experimental results showed that, when the environmental pressure in the sample ablation cell was risen to 0.5 MPa, the spectral intensity and signal-to-background ratio of metal plasma increased by 1.6-2.3times and 28%-47% respectively compared with ordinary pressure; while the plasma electronic temperature increased 1800K compared with 0.1MPa. It proved that the application of high ambient pressure could improve the ability of exciting the sample evaporant.3. Effects of different atmosphere on the emission characteristics of laser-induced stainlesss teel plasmasIn this experiment, the effects of Ar, N2, CO2 and Air atmosphere on the emission characteristics of stainless steel plasmas was studied. Experimental results showed that, when Argon is used as surrounding atmospheres, plasma spectral intensity showed an obvious enhancement, namely, plasma spectral intensity increased by 1.74～3.03 times compared with common air used as ambient gas, and signal-to-background ratio improved by 12%～26%; while plasma temperature and electronic density increased by 1080K and 0.91×1017cm-3 respectively. Comparatively speaking, the plasma radiation in N2 and CO2 were close to that in air.4. The application of laser-induced breakdown spectroscopy in quantitative analysisA series of national standard nickel-chromium-molybdenum-vanadium-titanium steel samples were used as targets. The emission spectra of laser plasma were measured in Ar at atmospheric pressure and then calibration curves were plotted. The Mn,Ti and Ni in measured samples were analyzed. Under the condition of deducting the spectral background, the relative standard deviations of five measurement results were found to be 4.58%,8.11% and 3.80%, and the average relative error were 6.41%,5.92% and 5.64% respectively. While, under the condition of non-deducting the spectral background, the relative standard deviations were found to be 4.54%,6.67% and 3.56%, and the average relative error values were 3.59%, 8.71% and 2.55% respectively. This demonstrates that non-deducting the spectral backgrounds can get more accurate analysis when the backgrounds are weak.