透镜与样品之间距离对激光等离子体辐射特性的影响

采用高能量钕玻璃激光器产生的激光(～25J)在减压氩气环境下诱导钢和土壤样品等离子体，研究了激光束聚焦透镜(f=130 mm)与样品之间距离对等离子体辐射特性的影响。实验结果表明，当聚焦透镜的焦点围绕样品表面上下移动时，对于合金钢样品，激光束焦斑位于样品表面以下0.4 mm左右，则激光等离子体的辐射强度、激发温度和物质烧蚀质量均出现最大值;而对于土壤样品，当激光束聚焦位置在样品表面以下0.2 mm左右，等离子体辐射强度和物质烧蚀质量具有最大值。为了比较透镜与样品之间距离对等离子体形状的影响，也拍摄了氩气和空气环境下产生的激光等离子体象。所得结果证明，激光等离子体特性明显依赖于透镜与样品之间距离。

Effect of Lens-to-Sample Distance on Laser-Plasma Radiative Properties

In the present paper, the effect of lens-to-sample distance (LTSD) on the radiative properties from the plasma induced by a high-energy neodymium glass laser (approximately 25J) in the argon ambient gas at a pressure of 0.43 x 10(5) Pa was studied. The experimental results showed that when the focus point of the focusing lens (f = 130 mm) shifts above and below the sample surface, the radiation intensities of the plasma, the excitation temperature, and the mass of ablated material are all changed, and their maxia appear at a focusing location of the laser beam, which is about 0.4 mm under the sample surface for alloyed-steel samples. If soil samples are used as the targets, the emission intensities of the laser plasma and the mass of ablated material have the maxima at a focus position about 0.2 mm below the sample surface. To investigate the influence of LTSD on the shape of the laser plasma, the images of the plasma formed have been shot in argon and air for the alloyed-steel samples. From these results, it was found that the properties of the laser plasma depend strongly on the LTSD.