Charge state and Energy distribution of carbon ions and protons emitted from laser-produced graphite plasma

The energy and charge state distribution of atomic carbon ions, carbon cluster ions, and protons emitted during Q-switched Nd:YAG laser (1064 nm/6 ns) laser irradiation of high purity graphite target was investigated by employing a time of flight ion energy analyzer (TOF-IEA). Laser fluence on the target surface was varied from 2 to 26 J cm(-2). At the lower fluence range (2-6 J cm(-2)), multiply charged low mass odd numbered cluster ions C-n(q+) with n = 3, 5, 7 and charge state up to 5 + and carbon atomic ions up to the charge state of 3 + were detected. For the fluence greater than 6.4 J cm(-2), carbon atomic ions up to a charge state of 6 + and protons were observed. The energy distribution of various carbon ions and protons was measured at the fluence of 5.1 and (2)5.5 J cm(-2). At 5.1 J cm(-2), the measured energy range for carbon cluster ions C-3(q+) and carbon C-1(q+) was 0.2-3.1 keV and 0.2-1.2 keV, respectively. At 25.5 J cm(-2), the energy of carbon ions C-1(q+) (q = 2-4) was in the range of 0.4-3.8 keV. Surprisingly, energetic protons with maximum energy of 1.5 keV and considerable intensity were detected at 25.5 J cm(-2). The bi-component structure of ion energy distribution suggested a complex ion accelerating mechanism, which is discussed within the framework of the electrostatic model.

Automated summary

The distribution of energy and charge state of carbon ions, carbon cluster ions, and protons produced during laser irradiation of graphite was investigated. Different charge states and energy ranges were observed for these ions at various laser fluences. The presence of energetic protons at a high laser fluence was surprising. The complex ion accelerating mechanism was discussed within the framework of the electrostatic model.