透镜到样品的距离对激光诱导等离子体的影响

Influence of the Lens-to-Sample Distance on Laser-Induced Plasma

利用具有时间分辨功能的ICCD相机对空气中激光诱导击穿合金钢产生的等离子体成像,同时采集了等离子体产生的发射光谱,针对焦距为100mm的聚焦透镜,研究了透镜到样品的距离(LTSD)对发射光谱强度、等离子体温度和等离子体形态的影响,并分析了产生影响的物理机制,对透镜到样品表面5个不同距离下等离子体光谱信号在样品表面垂直方向上的空间演变进行了分析。结果表明,透镜到样品的距离对等离子体的光谱信号、等离子体形态以及空间分布具有较大的影响。等离子体图像的像素强度与等离子体温度的变化规律基本一致,分别在透镜距离样品表面92mm和107mm处取得峰值,而92mm处对应最大值。对样品表面垂直方向上等离子体光谱信号的空间分布研究结果表明,不同聚焦位置下所产生的等离子体温度的空间分布不同,等离子体中不同谱线的光谱强度在空间的演变规律也有差别。

The behavior of the plasma induced by a laser on an alloy steel sample in air is observed by a time-resolved ICCD camera, and the plasma emission spectrum is simultaneously measured. The influences of the lens-to-sample distance （LTSD） on the plasma emission intensity, the plasma temperature and the plasma structure are investigated for a lens of 100-mm focal length. Its physical mechanism is studied, and the spatial distributions on the direction perpendicular to the sample surface are carried out for five different focal positions. It is demonstrated that the lens- to-sample distance has a considerable impact on the spectral signal, the plasma structure and the spatial distribution. The results show that the change of pixel intensity on the plasma image is consistent with that of the plasma temperature. The curves appear two peaks at the position of 92 mm and 107 mm respectively, and the values reach their maximum at 92 mm. It＇ s shown that the spatial distributions of the plasma temperature vary with LTSD on the direction perpendicular to the sample surface. Space evolutions of the different spectral lines in the plasma are also different.