Sasaki Yo, Wagatsuma Kazuaki
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Anal Sci. 2009 Apr;25(4):481-5. doi: 10.2116/analsci.25.481.
A time-resolved spectrometric measurement was conducted to determine temporal variations in the excitation temperature within a single laser plume caused by a Nd:YAG laser plasma. The two-line method using copper atomic lines was employed to estimate the excitation temperature. Two line pairs of copper lines: Cu I 521.82/Cu I 510.55 and Cu I 515.32/Cu I 510.55, were measured by using an Echelle spectrograph equipped with an ICCD detector having a high-speed gating. The excitation temperature was gradually elevated with the progress of the plasma expansion. This result cannot be explained from a direct excitation model in which excited species are principally produced through collisions with energetic particles, but from an indirect excitation model in which second-kind collisions with argon metastables and subsequent step-wise de-excitations produce the excited species. In the latter case, high-lying states of copper atoms are more populated compared to the population expected from the Boltzmann distribution. Temporal variations in the emission intensities of copper atomic lines requiring large excitation energies were also measured, and their emissions remained even in the expansion stage of the laser-induced plasma. This result also implies the over-population of high-lying copper excited levels.
进行了时间分辨光谱测量，以确定由钕钇铝石榴石（Nd:YAG）激光等离子体产生的单个激光羽流内激发温度的时间变化。采用利用铜原子线的双线法来估算激发温度。通过使用配备有具有高速选通功能的ICCD探测器的阶梯光栅光谱仪，测量了两对铜线：Cu I 521.82/Cu I 510.55和Cu I 515.32/Cu I 510.55。随着等离子体膨胀的进行，激发温度逐渐升高。这一结果不能用直接激发模型来解释，在直接激发模型中，激发态主要通过与高能粒子的碰撞产生，而要用间接激发模型来解释，在间接激发模型中，与氩亚稳态的第二类碰撞以及随后的逐步去激发产生了激发态。在后一种情况下，与玻尔兹曼分布预期的布居数相比，铜原子的高能态有更多的布居。还测量了需要大激发能量的铜原子线发射强度的时间变化，并且它们的发射在激光诱导等离子体的膨胀阶段仍然存在。这一结果也意味着高能铜激发能级的布居数过多。
