Study On The Spectral Quality Of The Plasma Induced By High-energy Laser

Laser induced -plasma is a very complex process. It strongly depends on many factors. In this experiment , a neodymium glass laser is used to study the effects of the operating voltage, power density, the height from the observed location of the plasma to the surface of the sample, the location of the sample, the gas composition and the pressure on the intensity and quality of the spectrum. The optimized experimental conditions are determined and the densities of some elements in the mental alloy standard samples are measured .The experimental results shows that the spectral intensity of the plasma enhances significantly with the increase of the operating voltage and the power density.(1) To the steel ally sample, the emission intensities of the spectra reach to the maximum values when the laser operating voltage is 1600V and the argon pressure is 600 torr. Under the same pressure, the spectral intensity of the plasma in the argon atmosphere is stronger than that in the air. When the argon pressure is 320 torr, the signal-noise ration is about 5 times than that which the argon pressure is 700 torr, but the temperature of plasma is less about 1000k. That is to say, the temperature increase with the increase of the atmospheric pressure. If the focal point of the len shifts around the surface of the sample, the mass ablation, the temperature of the plasma and the spectral intensity appear asymmetric and their maximum occur at the location which is about 0.4mm under the surface of the sample. (2) To the plasma of the aluminum alloy sample, when the operating voltage is 1600V,the height from the observed location of the plasma to the surface of the sample is 2mm and the argon pressure is 660 torr, the spectral intensity have the maximum values. The self-absorption ability of the Al(I)308.22nm and A(I)309.27nmlines is strengthen with the increase of increase of the pressure, and even appear self-reversal when the pressure is 600-700 torr.As the use of the laser induced-plasma , we determine the densities of the Mn, Ni, Ti elements in the 6-3 steel alloy standard sample and the Zn element in the 715 aluminum alloy, The Relative Standard Deviation(RSD) are respectively 5.949%,4.779%,5.214%,3.749%.and the relative errors are lower than 10.7%. Thisshows there is a good linear relation between the spectral intensity and the elemental density.