Abstract
In order to measure tungsten isotopic composition in presolar stardust grains that contain a limited number of atoms, we developed a new three-photon three-color resonance ionization scheme using titanium–sapphire lasers and the Laser Ionization of Neutrals (LION) instrument at Lawrence Livermore National Laboratory. The first two transitions can be easily saturated, while approximately 84% of available atoms can be ionized in the third transition with our current laser irradiance. When ionizing from the ground state, measurements demonstrate a W useful yield of 14.4% ± 1.6%. Experiments that intentionally cover a range of laser power and wavelength to simulate potential variations during analysis show that laser-induced W isotopic fractionation, if it occurs, is within measurement error. Overall, this new W resonance ionization scheme can be employed in future studies of atom limited samples to obtain W isotopic measurements.