Laser ablation of graphite at 355 nm: cluster formation and plume propagation

Ablation dynamics of C(n)(+) ions ejected from a 355-nm laser ablation of graphite target in vacuum has been investigated by time-of-flight (TOF) mass spectrometry. At 0.5 J/cm(2) laser fluence, the larger cluster ions are predominantly produced. With increasing laser fluence, however, the maximum size distribution moves toward small cluster ions. A strong nonlinear dependence of the amount of desorbed C(n)(+) cluster ions on laser fluence is observed under moderate laser fluence conditions (less than or equal to 1 J/cm(2)). This is interpreted by the mechanism that C(n)(+) ions are produced directly from the graphite via conversion of the multiphoton energy into thermal energy. The time resolved analysis of the ablated C(+) ions shows the two drift velocities with the fast and slow components. The result indicates that the ejecta emitted above the target surface separates into two components during plume propagation. (Int J Mass Spectrom 189 (1999) 115-123) (C) 1999 Elsevier Science B.V.