PLUME DYNAMICS IN TEA CO₂ LASER ABLATION OF POLYMERS AND GRAPHITE

Streak photography of TEA-CO₂ laser ablation of graphite and polymers in helium and argon background gases showed two luminous fronts lifting off the ablation targets at delayed intervals. The first luminous front was driven by the plume from the immediate ablation of top surface layer of polymer, while the second front by the delayed ejection of laser-decomposed, heavy fragment of polymeric materials which lasted for more than a few hundred µs. The dynamics of these two luminous fronts were complicated by the onset of the laser-supported absorption wave at higher background gas pressure of > 50 mbar Ar, as seen in nanosecond dye-laser shadowgraphy. Optical emission spectroscopy of spatial-temporal distribution of the first plume fitted with the shifted Maxwellian-Boltzmann distribution and implied plume splitting or the presence of two-velocity components of plume specie.

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