Kinetics of Ions Emitted From Nanosecond-Pulsed Laser-Generated Plasma in Broad Range of the Laser Fluence

Carbon plasma was produced by irradiating a graphite target with nanosecond-pulsed Nd:YAG laser beam in the broad range of the laser fluence (25– $2196\,\,\text {J}\cdot \text {cm}^{-2}$ ). A time resolving flat Langmuir probe was used to record the carbon ion pulses. For the investigated range of laser fluence, approximately three orders of magnitude increase in total ion charge (0.03– $2.74~\mu \text{C}$ ) and peak ion energy (4–492 eV) was observed. The ion pulses were deconvoluted using Coulomb–Boltzmann-shifted time function to estimate the number of ion charge states and ion energy of various charge states. The number of available ions charge states in the plasma was found to gradually increase with the laser fluence and C ⁶⁺ was observed only at the laser fluence of $2196\,\,\text {J}\cdot \text {cm}^{-2}$ . At a given laser fluence, peak energies of the ions are proportional to their charge state. The observed correlation between ions charge state and ions energy points toward the definite electrostatic acceleration mechanism. The equivalent ion accelerating potential was estimated for various values of the laser fluence and compared with the available literature data. These findings are quite useful for the development of laser plasma-based ion sources.