Time-of-flight mass spectrometric studies on the plume dynamics of laser ablation of graphite

Time-of-flight mass spectrometry has been used to probe neutral and positive ionic species produced by 266 nm laser ablation of graphite. At the laser fluence of 0.4-2.8 J/cm ², C ₃ was the major neutral species and C ⁺ and C ₃⁺ were the major ionic species. The arrival time distribution of C ₃ at 0.4 J/cm ² was fitted with a thermal Maxwell-Boltzmann (MB) distribution. As the laser fluence was increased, a shifted MB distribution with a narrower width provided a better fit, indicating an influence of collisions of ablated species in the laser plume. For the arrival time distributions of C ⁺ and C ₃⁺ at 0.9-1.3 J/cm ², a shifted MB distribution with higher velocities than those of C ₃ provided better fits. We discuss the expansion dynamics of the ablated species in the laser plume.