Line broadening mechanisms in the low pressure laser-induced plasma

The spectral profiles of Ca and Rb lines have been studied in a laser induced plasma as a function of pressure (1-10 torr) and delay time with respect to the plasma initiation (1-10 mu s). Measurements were made in a plasma induced by the 1064-nm output of a Nd:YAG laser on a calcium carbonate matrix, doped with Rb. Spectral profiles were measured in absorption using a narrow-band cw Ti:Sapphire laser. It was shown that in the case of a trace element (Rb in a CaCO3 matrix), the broadening mechanism was Doppler-dominant, whereas for a major matrix component (Ca), resonance broadening was the main contributor to the line shape, The plasma was shown to be non-equilibrium provided by the difference between the kinetic (3000 K) and the excitation (8000 K) temperatures. The electron number density at delay times of 5-10 mu s and pressures of 1-10 torr was estimated not to exceed 10(15) cm(-3). The number densities of Ca atoms in the ground and the excited (23 652 cm(-1)) states were evaluated by measuring line width and peak absorption at 732.6 nm, They were found to be in the range of (1.5-2.2) x 10(17) cm(-3) for the ground state and (1.5-33) x 10(11) cm(-3) for the excited state. (C) 1999 Elsevier Science B.V. All rights reserved.