不同实验条件对激光诱导等离子体的影响机理研究

常温常压下,采用波长532 nm的Nd:YAG纳秒激光器激发诱导空气中的铝合金,由高分辨率的光谱仪和ICCD对等离子体发射光谱采集和实现光电转换。研究激光能量、ICCD门延迟和聚焦透镜到样品表面的距离(lens-to-sample distance,LTSD)对谱线信号强度和等离子体电子温度的影响,并分析了产生影响的物理机制。结果表明,固定ICCD门延迟和LTSD,随着激光能量的增大,谱线强度和电子温度均增大;计算结果表明,当激光能量从20 mJ增加到160 mJ时,原子谱线Al I 396.15 nm,Mg I 518.36 nm,离子谱线Mg II 279.54 nm谱线强度相较于20 mJ分别提高了12.83,6.45,10.56倍。固定激光能量和LTSD,ICCD门延迟在100~4000 ns范围内变化时,随着延迟的增加,谱线强度和等离子体电子温度均呈指数形式衰减。固定ICCD门延迟和激光能量,采用焦距为75 mm的聚焦透镜,研究了LTSD对等离子体参数的影响机理。结果表明,聚焦透镜到样品的距离对等离子体的谱线强度和电子温度有较大的影响。等离子体的特征谱线强度和等离子体的电子温度的变化规律基本一致,分别在聚焦透镜到样品表面的距离为73 mm和79 mm处取得峰值,并在73 mm处对应最大值。

Study on mechanism of effect of different experimental conditions on laser-induced plasma

Under normal pressure and temperature,aluminum alloy in air can be excited by Nd:YAG nanosecond laser with wavelength 532 nm,the collection and photoelectric conversion of the plasma emission spectrum are executed by a high-resolution spectrometer and an ICCD.This paper studies the influences of laser energy,ICCD gate delay and lens-to-sample distance(LTSD)on the spectral intensity and plasma electron temperature as well as the physical mechanism.It is demonstrated that the spectral intensity and electron temperature increase with the increase of laser energy at the fixed ICCD gate delay and LTSD.The calculated results show that when the laser energy increases from 20 mJ to 160 mJ,the line intensities of the atomic spectral lines Al I 396.15 nm,Mg I 518.36 nm,and the Mg II 279.54 nm ion spectral line are 12.83,6.45 and 10.56 times higher than that of 20 mJ,respectively.At the fixed laser energy and LTSD,when the ICCD gate delay changes within 100-4000 ns,the spectral intensity and plasma electron temperature decay exponential with the increase of ICCD gate delay.With the same ICCD gate delay and laser energy,the influence mechanism of LTSD on plasma parameters was studied by using a focusing lens with focal length of 75 mm.It is demonstrated that the lens-to-sample distance has a considerable impact on the spectral intensity and plasma electron temperature.The results indicate that the change of the spectral intensity is consistent with that of the plasma electron temperature.The curves have two peaks at the distances of 73 mm and 79 mm from sample surface,and the values reach their maximum at 73 mm.