Measurement of carbon plasma plume for optimization of the process carbonaceous functional materials

利用KrF准分子激光（λ=248 nm）和Nd:YAG激光（λ=532 nm）在真空条件下烧蚀石墨靶，产生碳等离子体羽流。采用2D-LIF、光谱吸收法和离子探针法测量了C_2分子、C原子和C^+的相对密度及其分布。实验结果总结如下：KrF激光烧蚀从石墨中喷射出的C原子和离子处于高电子激发态。离子数量随激光辐照度的增加而增加，并在烧蚀后100 ns内发生辐射复合。Nd:YAG激光从C， C^+产生的等离子体羽流发射。C、C^+、C_2的数量随激光辐照量的增加而增加。3)烧蚀后300 ns， KrF等离子体羽流中C_2分子的温度约为2870 K，高于Nd:YAG等离子体羽流。Nd:YAG基激光器通过加热和蒸发石墨靶产生C， C^+, C_2。用Nd:YAG激光（λ=532 nm）在500 Torr氩气中烧蚀含Ni石墨复合棒，形成碳纳米管条件下等离子体羽流的光学测量。用C， C_2, C^+, C^<2+>的发射谱线观测了Ar， Ni的许多原子发射谱线。在烧蚀后的400 ns，大部分碳原子的发射都消失了，而Ni原子的发射却持续了很长时间，这表明存在受激的Ni原子。激光Mie散射图像显示，碳颗粒在烧蚀后以7 m/s的初始速度在靶材附近形成几百μs，并在几十ms内扩散形成漩涡。

Carbon plasma plumes are produced by ablating a graphite target using KrF excimer laser (λ=248 nm) and Nd:YAG laser (λ=532 nm) in vacuum. Relative densities and their profiles of C_2 molecules, C atoms and C^+ were measured using 2D-LIF, spectral absorption method and ion probe method. Experimental results are summarized as follows.1) C atoms and ions ejected from a graphite by KrF laser ablation are in highly electronically excited states. Number of ions increases with increase of laser fluence and they play radiative recombination within 100 ns after ablation.2) Emission from plasma plume produced by Nd:YAG laser from C, C^+. The number of C, C^+, C_2 increase with laser fluence.3) Temperature of C_2 molecules in KrF plasma plume is about 2,870 K at 300 ns after ablation, which is higher than that of Nd:YAG plasma plume. Production of C, C^+, C_2 by Nd:YAG fundamental laser results from heating and evaporation of a graphite target.Optical measurement of plasma plume under carbon nanotubes formation condition, where a graphite composite rod containing Ni was ablated by Nd:YAG laser (λ=532 nm) in 500 Torr Ar gas. Many atomic emission lines of Ar, Ni were observed with emission from C, C_2, C^+, C^<2+>. Most of emission from carbonaceous species extinguish at 400 ns after ablation, however, Ni atomic emission lasts for long time and it indicates existence of excited Ni atoms. Laser Mie scattering images showed that carbon particulates are formed near the target at about several hundreds μs after ablation and drift at initial velocity of 7 m/s and diffuse forming swirls few tens ms.