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

Abstract

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 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 25.5 J cm−2. At 5.1 J cm−2, the measured energy range for carbon cluster ions and carbon was 0.2–3.1 keV and 0.2–1.2 keV, respectively. At 25.5 J cm−2, the energy of carbon ions (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.