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 ( 2 )对于标准铝样品，在激光器工作电压为1600v 、等离子体观测高度为2mm 、氩气压力为660乇时，其谱线强度最强；以al 308 . 22nm 、 al 309 . 27nm两条谱线为分析线，发现随着环境气压的增大，谱线自吸效应明显增强，当环境气压达到600 - 700乇时，谱线几乎产生自蚀。
2.
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 to rr , 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 ( 1 )对于光谱标钢准样品，当激光器工作电压为1600v 、氩气压力为600乇时，谱线强度达到最大，并且在相同压强下，氩气中的等离子体与空气中的等离子体相比，其辐射强度明显增强；氩气压力为320乇时的谱线信背比约为600乇条件下的5倍，而等离子体温度却下降了近1000k ，即等离子体温度随环境气压的增大而增大；当激光束的焦斑在样品表面上下移动时，激光诱导量、等离子体的激发温度、谱线强度都呈不对称性分布，其最大值对应的焦斑位置都位于样品表面之下0 . 4mm左右。
