样品的激光诱导击穿光谱及谱线的自吸收现象

以脉冲Nd∶AG激光器的二倍频输出为激发源，获得了一种家庭用煤的激光诱导击穿光谱(laser induced breakdown spectrum，LIBS)。通过对谱线的归属，发现该煤种除包含文献报道的C，Si，Mg，Fe，Al，Ca，Ti，Na，K元素外，还包含Cd，Co，Hf，Ir，Li，Mn，Ni，Rb，Sr，V，W，Zn，Zr等微量元素，谱图中没有出现对应H和O元素的谱线，把该现象归因于H和O原子的跃迁概率较小，而灵敏谱线对应跃迁的上能级能量较大。同时发现随激光脉冲能量的增加，等离子体发射谱线的强度增大，增加到一定程度，K原子766.493和769.921 nm谱线会出现自吸收现象，自吸收的程度随激光能量的增加而增强，出现明显的双峰结构，把自吸收现象归因于原子大的跃迁概率及激光强度增加引起等离子体中粒子数密度的增大。

Laser Induced Breakdown Spectra of Coal Sample and Self-Absorption of the Spectral Line

The LIBS of one kind of household fuel coal was obtained with the first harmonic output 532 nm of an Nd·YAG laser as radiation source. With the assignment of the spectral lines, it was found that besides the elements C, Si, Mg, Fe, Al, Ca, Ti, Na and K, which are reported to be contained in coal, the presented sample also contains trace elements, such as Cd, Co, Hf, Ir, Li, Mn, Ni, Rb, Sr, V, W, Zn, Zr etc, but the spectral lines corresponding to O and H elements did not appear in the spectra. This is owing to the facts that the transition probability of H and O atoms is small and the energy of the upper level for transition is higher. The results of measurement also show that the intensity of spectral line increases with the laser pulse energy and self-absorption of the spectral lines K766.493 nm and K769.921 nm will appear to some extent. Increasing laser energy further will make self-absorption more obvious. The presence of self-absorption can be attributed to two factors. One is the higher transition rate of K atoms, and the other is that the increase in laser intensity induces the enhancement of the particle number density in the plasma.