激光诱导Mg等离子体电子温度的实验研究

利用波长为1 064 nm，最大能量为500 mJ的Nd∶YAG脉冲激光器在室温，一个标准大气压下对Mg合金冲击，改变激光能量，得到相应的Mg等离子体特征谱线。分析谱线，发现谱线有不同的演化速率，同时得到了MgⅠ，MgⅡ离子谱线，证明此实验条件下，激光能量足够Mg合金靶材充分电离。选择了相对强度较大的MgⅠ 383.2 nm, MgⅠ 470.3 nm, MgⅠ 518.4 nm三条激发谱线，利用这些发射谱线的相对强度计算了等离子体的电子温度，激光能量为500 mJ时，等离子体温度为1.63×104 K。实验结果表明：在本实验条件下，Mg原子可以得到充分激发;在200～500 mJ激光能量范围内，等离子体温度随着激光能量的降低而衰减，在350～500 mJ激光能量范围内的等离子体温度随激光能量的变化速度十分明显，200～350 mJ时等离子体温度变化速度迅速减缓;激光能量为300 mJ时，谱线相对强度明显减弱，低于350和250 mJ的谱线相对强度，不符合谱线相对强度会随着激光能量提高而上升的变化趋势，证明发生了等离子体屏蔽现象，高功率激光产生的等离子体隔断了激光与材料之间的耦合。此时的等离子体温度明显升高，不符合变化趋势，这是由于在发生等离子体屏蔽现象时，激光能量被等离子体吸收，导致等离子体温度上升。

Experimental Investigation on the Electron Temperature of Laser-Induced Mg Plasmas

A series of plasma characteristic spectral lines of Mg alloy were obtained under nanosecond laser shock produced by a pulsed Nd∶YAG laser (1 064 nm,maximum energy 500 mJ),which was taken under standard atmospheric pressure and at room temperature.Results indicated that the evolutionary rates of spectral lines were different,and the laser energy was enough to ionization Mg alloy under this experimental condition by the spectral lines of MgⅠ,MgⅡ.The electron temperature of Mg plasma were calculated by the measured relative Emission-line intensity(MgⅠ383.2 nm,MgⅠ470.3 nm,MgⅠ518.4 nm).The experimental results showed that the secondary excitation Mg atoms could be got under this experimental condition.The electron temperature of Mg plasma decreased with the laser energy reduced while the laser energy was in the range of 200~500 mJ. When the laser energy was in the range of 350~500 mJ,the electron temperature changed rapidly.When the laser energy was in the range of 200~350 mJ,the electron temperature changed slowly and tended towards stability.It is found that when the laser energy was 300 mJ,the plasma temperature raised suddenly,which could not accord with the trend because of plasma shielding. When the laser energy was 300 mJ,the relative intensity of spectral lines was reduced which was lower than that of 350 and 250 mJ.And it is against the variation trend of the relative intensity of spectral lines increases with the increase of laser energy, which prove plasma shielding phenomenon had occurred and plasma with high power laser separate the coupling between laser and material.The plasma temperature was increased significantly,which is not consistent with the trend .When the plasma shielding phenomenon happened,laser energy was absorbed by the plasma,resulting in the rise of plasma temperature.