Laser-induced ablation of a steel sample in different ambient gases by use of collinear multiple laser pulses.

The sensitivity of laser-induced breakdown spectroscopy of solid samples depends on the number of ablated and excited analytes. Laser ablation of solid samples can be enhanced by using collinear multiple laser pulses, for example double or triple pulses, rather than single laser pulses with the same total laser pulse energy. The ablation rates and the plasma conditions are affected by the ambient gas. In this study laser ablation was examined by varying the interpulse separation of the multiple pulses, within double and triple-pulse bursts, and the gas mass density at constant gas pressure. Different ambient gases and gas mixtures consisting of argon, oxygen, and nitrogen were used to study their effect on ablation rates. In a pure argon atmosphere (99.999% v/v Ar) the ablation burst number required to penetrate a steel plate of thickness 100 microm is reduced by a factor of approximately six by use of triple-pulse bursts with a symmetric interpulse separation of 15 micros rather than single pulses with the same total burst energy of 105 mJ. For double and single pulses the factors are 1.6 for Ar and 2.8 for synthetic air. Analyte lines are 4 to 8 times more intense if an argon atmosphere, rather than air, is used.