不同样品温度下聚焦透镜到样品表面距离对激光诱导铜击穿光谱的影响

研究了不同温度下聚焦透镜到样品表面距离对激光诱导击穿光谱(laser-induced breakdown spectroscopy,LIBS)强度的影响,使用Nd:YAG脉冲激光激发样品并产生等离子体,探测的等离子体发射的光谱线为Cu(Ⅰ)510.55 nm,Cu(Ⅰ)515.32 nm和Cu(Ⅰ)521.82 nm.使用透镜的焦距为200 mm,测量的聚焦透镜到样品表面距离的范围为170—200 mm,样品温度从25℃升高到270℃,激光能量为26 mJ.总体上,升高样品温度能有效地提高LIBS光谱的辐射强度.在25℃和100℃时,光谱强度随着聚焦透镜到样品表面距离的增加而单调增加;在样品温度更高(150, 200, 250和270℃)时,光谱强度随着距离的增加出现先升高而后又降低的变化.同时,在样品接近焦点附近,随着样品温度的升高,LIBS光谱强度的变化不明显,还可能出现光谱强度随着样品温度升高而降低的情况,这在通过升高样品温度来提高LIBS光谱强度中特别值得我们注意.为了更进一步了解这两个条件对LIBS的影响,计算了等离子体温度和电子密度,发现等离子体温度和电子密度的变化与光谱强度的变化几乎一致,更高样品温度下产生的等离子体温度和电子密度更高.

Influence of distance between focusing lens and sample surface on laser-induced breakdown spectroscopy of brass at different sample temperatures

From previously published results of laser-induced breakdown spectroscopy, one can know that the change in the distance from the sample surface to the focusing lens has an important influence on the interaction between the sample and the laser, and increasing the sample temperature can enhance the coupling between the laser and the sample. However, almost no work has devoted to directly studying the influence of the distance between focusing lens and sample surface on the spectral intensity of laser-induced breakdown spectroscopy under different sample temperatures. In this paper, we investigate experimentally this subject. An Nd:YAG laser is used to excite the sample to produce the plasma. The detected spectral lines are Cu (I) 510.55 nm, Cu (I) 515.32 nm, and Cu (I) 521.82 nm. The focal length of focusing lens is 200 mm. The distance between focusing lens and sample surface ranges from 170 mm to 200 mm. The sample is heated from 25 ℃ to 270 ℃, and the laser energy is 26 mJ. In general, the spectral intensity of laser-induced breakdown spectroscopy can be effectively enhanced by increasing the sample temperature. At the sample temperatures of 25 ℃ and 100 ℃, the spectral intensity increases monotonically with the increase of the distance between focusing lens and sample surface; at higher sample temperatures (150, 200, 250, and 270 ℃), the spectral intensity first increases and then decreases with the increase of the distance between focusing lens and sample surface. In addition, near the focal point, with the increase of sample temperature, the increase of the spectral intensity is not obvious, and the spectral intensity decreases with the increase of sample temperature, which is particularly noteworthy in improving the spectral intensity of laser-induced breakdown spectroscopy by increasing sample temperature. In order to further understand the influences of these two conditions on laser-induced breakdown spectroscopy, we also calculate the plasma temperature and electron density, and find that the variation of plasma temperature and electron density are almost the same as that of spectral intensity. The plasma temperature and electron density at higher sample temperature are higher.