Optical Emission from Laser-Induced Breakdown Plasma of Solid and Liquid Samples in the Presence of a Magnetic Field

The optical properties of laser-induced plasma generated from solid (Al alloy) and liquid (Mn, Cr, Mg, or Ti solutions) samples expanded across an external, steady magnetic field have been studied by atomic-emission spectroscopy. Various line emissions obtained from the constituents of the Al alloy and of the aqueous solution show an enhancement in intensity in the presence of an ~5-kG magnetic field. The enhancement of the signal was nearly a factor of 2 for the minor constituents of the solid samples and a factor of 1.5 for the elements in liquid phase. Temporal evolution of the emission from the solid sample showed maximum enhancement in emission intensity at 3 -10- (mu)s time delay after plasma formation in the laser energy range 10 -50 mJ. However, for the liquid sample the maximum signal was for a gate delay of 3 -25 (mu)s in the energy range 50 -200 mJ. This enhancement in the emission intensity was found to be due to an increase in effective density of the plasma as a result of magnetic confinement when the plasma cooled after expansion. This enhanced emission was due to an increase in the rate of radiative recombination in the plasma.