Abstract

Femtosecond near-infrared (NIR, 1030 nm) and near-ultraviolet (NUV, 257 nm) laser ablation (fs-LA) were evaluated for U-Pb dating of zircons using inductively coupled plasma mass spectrometry (ICP-MS). The apparent ages are in agreement with the reference ages, within expanded combined uncertainties, at both wavelengths, but NIR fs-LA produces poorer uncertainties and a approximate to 3.5% bias on the reference age of Mudtank and Plesovice zircon. The time resolved U-238 signal intensity rises sharply and progressively decreases in NUV, whereas patterns in NIR follow progressive increase and then decrease during ablation. Synchrotron X-ray microtomography (XRMT) imaging of an ablated quartz permitted to link the morphology and dimensions of fs-LA craters to the performances of fs-LA-ICP-MS analyses on zircons. Average ablation rates are similar at 3 J.cm(-2) for both wavelengths. However, the ablation rate is higher in NIR at 7 J.cm(-2) than in NUV at 2 J.cm(-2), whereas the fs-LA-ICP-MS yield (in counts.shot(-1).ppm(-1)) is lower in NIR at 7 J.cm(-2) than in NUV at 2 J.cm(-2). This paradox as well as the biased or imprecise fs-LA-ICP-MS analyses are explained by nonlinear shot-to-shot ablation in NIR compared to NUV, induced by: (i) catastrophic ablation, (ii) incubation effects, and, to a minor extent (iii) preferential ionization of U relative to Pb. Consequently, NIR fs-LA is capable of producing accurate U-Pb ages thanks to the properties of femtosecond laser matter interactions, but with a higher fluence, sample consumption and poorer statistics than those obtained with NUV fs-LA.