缓冲气压对CO_2激光Al靶等离子体参量的影响

Analysis of the properties of CO_2 laser-induced aluminum plasma at different ambient pressures

为了研究缓冲气压对激光等离子体参量的影响,利用CO_2,激光烧蚀A1靶产生等离子体,缓冲气压变化范围为10^(-4)Pa～2×10~3Pa,激光脉冲能量为180mJ/脉冲,在局域热平衡和光学薄等离子体假设下,采用发射光谱法计算了等离子体的电子温度和电子密度,并研究了缓冲气压对这些参量的影响。结果表明,等离子体的电子温度和电子密度分别在1.05eV～2.47eV与1.95×10^(16)cm^(-3)～10.5 × 10^(16)cm^(-3)范围内,Al等离子体的电子温度随气压的增大而减少;低缓冲气压时,电子密度随气压增大而减小,当气压达到600Pa时,激光脉冲会击穿空气形成等离子体,电子密度又开始上升,当气压超过3000Pa时,空气等离子体会屏蔽激光脉冲能量,使到达靶面的激光能量急剧下降,Al原子的特征谱线也随之减弱而几乎消失。这一结果对理解缓冲气压对激光与物质相互作用过程的影响是有帮助的。

In order to study the properties of laser-induced plasma at different ambient pressures, emission spectroscopy was studied on aluminum plasma generated by CO2 laser with energy of 180mJ/pulse at different air ambient pressures. The dependency of plasma temperature and density on ambient pressures were estimated from the analysis of spectral data by assuming the conditions of local thermodynamic equilibrium and optically thin plasma. Electron temperature was measured in the range of 1.05eV -2. 47eV, and electron density was measured in the range of 1.95×10^16cm-3-10.5×10^16cm-3 as the ambient pressure was varied from 10-4Pa to 2 ×10^3pa. The results show that the plasma temperature decreases with the ambient pressures. At first, the electron density decreases with the increase of ambient pressure under low pressure. When the pressure reaches 600Pa, the broken air plasma may interact with A1 vapor and the electron density increases with the pressure increasing. For larger ambient pressure up to 3000Pa, the A1 emission lines eventually disappear, suggesting that the laser energy is almost screened by the air plasma. The results provide useful guidance to understand the influence of air pressure on laser-matter interaction.