Estimation of ion accelerating potential inside the nanosecond pulsed laser produced tungsten plasma

Plasma plume generated by neodymium-doped yttrium aluminium granite laser (wavelength= 1064 nm, pulse duration= 6 ns) focused onto a planar tungsten target is investigated with the help of ion collector (IC) and electrostatic ion energy analyzer (IEA) operating in time-of-flight configuration. Laser fluence was in the range of 7-20 J/cm(2). The IEA spectra showed that the charge state of tungsten ions emitted from the plume increases with the laser fluence and W6+ was the highest ion charge state detected in the investigated range of the laser fluence. Coulomb-Boltzmann-shifted time function was used to determine ion intensities and peak energies of the various ion charge states from the measured IC spectra. Depending on the charge state, the energies of various ion charge states were in the range of 0.6-2.7 keV. The experimental data were exploited to estimate the equivalent accelerating potential developed inside the plume. The equivalent accelerating potential was found to increase linearly with the increase of laser fluence. The comparison with literature data revealed that the equivalent accelerating potential also increases with the atomic number of the target material. These results are in good agreement with the predictions of the electrostatic model for ion acceleration in laser plasma.