Curves of growth of neutral atom and ion lines emitted by a laser induced plasma

The curves of growth of 11 Fe I lines and 10 Fe II lines emitted by a laser-induced plasma have been investigated. The plasmas have been generated with Fe-Ni alloys in air at atmospheric pressure using a Nd:YAG laser. The experimental curves measured at the time windows 1.0-1.5 μs and 3.0-3.5 μs have been reproduced by theoretical curves of growth calculated using a single reduced set of parameters that characterize the plasma, including the apparent temperature, the product N′l of the number density (normalized to 100% concentration) times the length of the plasma along the line-of-sight, and the product αA, which accounts for the perpendicular radiating area of the plasma and the instrumental factor due to the efficiency and the solid angle of the detection system. The plasma apparent (population averaged) temperatures for neutral atom and ion emissions at each time window have been obtained using a modified Boltzmann plot method, based on the replacement of the line intensities by the slopes of the low-concentration limits of the curves of growth, which avoids the systematic error due to self-absorption.