Double pulse laser-induced plasmas on W and Al by ps-LIBS: Focus on the plasma-second pulse interaction

The LIBS (laser-induced breakdown spectroscopy) method can be implemented to determine the multi-elemental composition of solid samples. Unfortunately, the precision of the usual LIBS configuration (single pulse) is rather low for light elements in metallic matrices. The double pulse configuration can help to overcome this difficulty. Indeed, the electron temperature and density are significantly increased by the second pulse absorbed by the plasma produced by the first pulse which leads to a higher signal-to-noise ratio. The present paper reports preliminary results in double pulse configuration on fusion-relevant materials, i.e. aluminum (considered as a beryllium surrogate) and tunsgten, in the perspective of the test of this technique to measure in situ the hydrogen isotopes concentration of the divertor and the first wall of an ITER-like tokamak. The plasma spectroscopic analysis is performed to derive the gain in electron density reached by the absorption of the second pulse. In parallel, the spectral absorptivity of the plasma regarding the second pulse is determined to correlate the electron density dynamics to the energy deposit. The absorption by the plasma of the second pulse is then quantified at the atomic and macroscopic scales.