Characterization of highly charged titanium ions produced by nanosecond pulsed laser

Abstract

In this work, plasma is produced by irradiating a Ti target with 10 ns pulsed Nd:YAG (λ = 1064 nm) laser. The laser fluence at the target was varied in the range of 2-20.3 J/cm2. The ion signal from freely expanding Ti plasma in vacuum was characterized with the help of ion collector and time-of-flight electrostatic energy analyzer. The ion charge state was found to increase with the laser fluence and maximum available ion charge in this fluence range is Ti4+. A correlation between the intensities of various ion charge states was observed, which indicates that higher charge states are most probably produced through stepwise ionization mechanism. It is also observed that charge state distribution of plasma can be controlled by variation of the laser fluence. In addition, energy distribution of ion charge states Tin+ (n = 1-4) is measured by varying back plate voltage of the electrostatic energy analyzer for a fixed laser fluence of 20.3 J/cm2. Ions energy distributions were in the range of 0.36-3.0 keV and the most probable ion energy was found to increase linearly with ion charge state. The estimated equivalent potential at the laser fluence of 20.3 J/cm2 is about 310 V. These results are in good agreement with the predictions of electrostatic model of ion acceleration in laser plasma.