Résumé
We studied the influence of pulse energy (E 0) and pulse width (s) of Near Infra Red femtosecond Laser Ablation coupled to Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). A particular emphasis was put on the 206 Pb/ 238 U and 208 Pb/ 232 Th repeatability from Moacyr monazite (Itambe, Brazil). Synthetic glass (Standard Reference Material) NIST610 was used as a reference material, as well as a monazite from Manangotry (Madagascar). Pulse energy was investigated in the range E 0 ¼ 0.03 to 0.8 mJ/pulse (s ¼ 60 fs) while pulse width has been studied from s ¼ 60 fs to 300 fs (E 0 ¼ 0.1 mJ/pulse). Data suggest that pulse width has no detectable influence on the accuracy and repeatability of measured elemental ratios in the range of 60-300 fs. Observed measurements repeatabilities are 2.5%RSD and 1.8%RSD for 206 Pb/ 238 U and 208 Pb/ 232 Th, respectively. At 60 fs, the 0.03-0.8 mJ/pulse energy range studied does not induce any detectable change in data accuracy and repeatability. Uncertainties of 1.1-2.8%RSD were obtained for 206 Pb/ 238 U. In the range of E 0 ¼ 0.1-0.8 mJ/pulse, matrix matched calibration using Manangotry monazite gives a similar good repeatability of 2.4%RSD for 206 Pb/ 238 U. No clear matrix effect could be highlighted.