Study of laser-induced-plasma parameters for molybdenum targets

Abstract

Molybdenum targets were irradiated with 2-ns 300-mJ pulses from an Nd:YAG laser at its second harmonic wavelength of 532 nm at a repetition rate of 10 Hz in open air. The radiation emitted from laser-induced plasma from the Mo target in the Local Thermal Equilibrium (LTE) state was analyzed. The temperature of the plasma was calculated using a Boltzmann-plot method. The electron density was determined from the Stark broadening via the comparison of the electron densities of different neutral molybdenum lines (465.5, 498, 517 and 550 nm) with hydrogen Hα-line (656.3 nm). We studied the variation of electron density and electron temperature as a function of μs-delay times and laser fluencies at different distances from the target surface. It was found that the neutral molybdenum lines suffer from self-absorption. The self-absorption changes the values of the electron density and the electron temperature due to the decrease in the line intensity and the increase in the line width and hence leads to the distortion in the line shape. The Mo I lines were corrected against self-absorption and the corrected values of the temperature and the electron density were obtained.