A spectroscopic study on the evaporation of aluminum as irradiated by a long-pulse Nd laser

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Abstract
The plasma plume produced by a focused Nd laser beam (1.06 μm, 43 J, 1.2 msec) on an aluminum plate in air at power densities up to 3×107 W/cm2 has been studied by the spectroscopic technique. The average speed of the luminous vapor jet is measured to be 8×103 cm/sec by the time-of-flight method. The emission spectrum, which consists mainly of Al and AlO, is similar to that from an electric arc. The temperature of the plasma is estimated to be ?1 eV fom a theoretical analysis of the equilibrium composition of the A1-O system in the gas phase. Of particular interest is the detection of optically forbidden transitions from the np (2P) and nf (2F) states to the 3p (2P) ground state of AlI due to the instantaneously high density and electric field. From the Stark shift of the self-reversed 4d lines, the ion density is estimated as 9×1017/cm3. These results suggest that laser evaporation may be a novel source for studying atomic and molecular spectra at high density.