Intensity enhancement in Double-Pulse Laser-Induced Breakdown Spectroscopy in vacuum

Single- and double-pulse laser-induced breakdown spectroscopy (LIBS) were carried out on carbon samples at low background pressures (10-3 Torr). Double-pulse experiments were performed with an orthogonal beam geometry on two targets. Conditions for intensity enhancement were analyzed as a function of delay between pulses and laser fluences. The optimal delay between pulses was found in the range from 2 to 5 μs. Compared to single-pulse LIBS, signal enhancements of approximately 2 for the C I 477.2 nm, 4 for the C II 426.7 nm and 6 for the C2 473.4 nm (Swan band head) lines were observed in double-pulse. For all species under consideration, intensification increased with the fluence of the first pulse. On the other hand, the fluence of the second pulse had different effects on atomic and molecular species