为研究土壤湿度对激光等离子体的影响, 通过制备六种不同湿度的土壤样品进行实验, 选取铅的特征谱线(Pb: 405.78 nm)为分析线。 实验结果表明, 随着土壤湿度的增加, 谱线的强度、 信噪比及RSD线性减小。 在局部热力学平衡近似下, 选取铁在400～440 nm波长范围内的四条特征谱线, 利用玻尔兹曼图, 测定了等离子体温度在不同湿度下的变化特性, 随着湿度从零增加到20%, 等离子体温度从11 800 K近似单调的下降到7 800 K, 电子密度从3.3×106 cm-3减小到2.8×106 cm-3。

The soil samples at six different humidities were prepared for studying the influence of soil humidity on laser-induced plasmas. By analyzing the characteristic spectral lines of Pb with the wavelength of 405.78 nm, it was demonstrated that the intensities of spectral line, SNR and RSD are linearly inversely proportional to the soil humidity. Under the approximation of local thermal equilibrium, by analyzing the characteristic spectral lines of Fe within the wavelength range of 400 to 440 nm, the temperature of plasmas was obtained by means of the two-dimensional Boltzmann plane. The experimental results show that the plasma temperature monotonously changes from 11 800 to 7 800 K and the electron density monotonously changes from 3.3×106 cm-3 to 2.8×106 cm-3, when the humidity increases from 0 to 20%.