液体射流双脉冲激光诱导击穿Ca等离子体温度和电子数密度研究

Temperature and Electron Number Density of Liquid Jet Double-Pulse Laser Induced Breakdown Ca Plasma

等离子体温度和电子数密度是激光诱导击穿光谱(LIBS)测量中的重要因素。采用两台532nm Nd…YAG脉冲激光器作为光源击穿CaCl2样品溶液液体射流形成等离子体,得到了300～450nm波段的发射光谱图,定性分析了Ca II离子发射谱线。实验中假设等离子体处于局部热平衡状态,根据LIBS公式,利用Ca的6条一价离子谱线的相对强度,通过Boltzmann斜线法得到了液体双脉冲LIBS等离子体温度约104 K,其等离子体电子温度和单脉冲LIBS相比要高,但和固体双脉冲LIBS相比略低。通过拟合Ca II 393.366nm离子线得到等离子体电子数密度约为1017 cm-3,并由实验结果讨论了等离子体温度和电子数密度随延时时间、脉冲间隔的变化规律,也证明了双脉冲LIBS较单脉冲LIBS更有优势。最后基于实验计算结果证明本实验的Ca等离子体满足局部热力学平衡。

Plasma temperature and electron number density are important factors of the laser-induced breakdown spectroscopy （LIBS） measurements. The plasmas are generated using two 532 nm Nd： YAG pulsed lasers to ablate the plasma breakdown liquid jet of CaCl2 solution. We get the spectrum of 300 - 450 nm band and analyze the Ca II emission lines. It is assumed that the plasmas produced in the experiment are in local thermodynamic equilibrium （LTE）, according to LIBS formula the Ca plasma temperature of 10^4 K is determined by using the Boltzmann plot method with 6 Ca II lines while the electron density of 10^17 cm^- 3 is obtained from the Stark broadening of Ca II 393. 366 nm line. The variations of plasma temperature and electron density with delay time and the time between two pulses are discussed based on experimental results. The advantage of double-pulse LIBS over single-pulse LIBS is proved. Experimental results show that the laser induced Ca plasma is in local thermodynamic equilibrium.