Diagnosis of Laser Ablation Plasma by Time- and Space-Resolved Laser Spectroscopic Measurements

点击翻译按钮获取中文摘要

Laser ablation is a technique to vaporize solid saBIPles such as metal, semiconductor, ceramics by focusing an output of a pulsed laser onto targets, and to produce atoms, molecules, ions, and so on. The purpose of this research project is to diagnose produced particles in plasma using laser spectroscopic methods such as emission, laser-induced-fluorescence (LIF), degenerated-four-wave-mixing (DFWM). Making use of a pulsed laser source with narrow bandwidth (below 0.0001 nm) and instantaneously strong power is essential for internal-state specific investigation of atoms and molecules in ablation plasma. In order to study dynamic behavior of molecular ions whose transition lines lie in UV region, we first of all, constructed a system of pulsed amplification of narrow-band cw lasers. The results of the investigations are as follows :(1) Doppler width of Si0^+ ions produced by laser ablation was measured with laser source described above and the temporal behavior of translational motion of Si0^+ ions was precisely observed. It was found that translational temperature of produced Si0^+ ions decreases and increases repeatedly before being thermarized to the room temperature within several hundred us. This indicates the first observation of plasma pulsatlon, nanely, the oscillation of the interface between Si ablation plasma and 0_2 atmospheric gas.(2) Alkali-earth ions such as Ca^+, Sr^+, Ba^+ were produced by laser ablation in He, H_2, or D_2 buffer gas and the temporal behavior of their internals tates were measured with LIF method. The energy separation of the fine-structure in the P excited state of Alkali-earth ions was found to play an important role to determine transition probabilities among fine-structure levels.(3) Special distribution of Al neutral atoms produced by laser ablation in the air was measured with DFWM method. It turned out that neutral atoms tend to reside in the outer part of the plasma plume.