Comparison between the characteristics of the plasmas generated by laser on solid and molten steels

Plasma characteristics, excitation temperatures of atomic iron and electron number densities, were compared between the laser-induced plasmas generated on solid steel at room temperature and molten steel. The excitation temperatures of iron atom were determined by Boltzmann plot using neutral iron atomic emission lines in the wavelength range of 386 to 400 nm. Electron number densities were estimated by measured linewidths of AlI394.4 nm. Excitation temperature of iron decreased from 10,800 K at 10 μs to 7300 K at 80 μs of delays for solid steel. Significant difference in the excitation temperatures of iron atom wasnʹt exhibited between the plasmas generated on solid and molten steels. The linewidths observed with molten steel were narrower than those observed with solid steel in most of neutral atomic lines of iron and aluminum. Electron number density in the plasma produced on molten steel was estimated to be (0.99 ± 0.15) × 1017 cm− 3, which was 46% of electron number density in the plasma on solid steel at the same observation delay of 10 μs from the laser pulse. The optical depths were obtained by evaluating the broadening due to self-absorption in the resonance line, FeI385.99 nm. The iron atom number density in the plasma induced on molten steel has been found to be 1.3 times that in the plasma induced on solid steel.