High resolution laser spectroscopy of metallic atoms and molecules: Storage of singly and doubly charged ions transferred from externally generated laser plasmas

A radio-frequency (RF) ion trap has been constructed for high resolution laser spectroscopy of metallic ions. Ions in externally generated laser plasma have been directly introduced into the RF ion trap. An Nd:YAG laser is used to vaporize and ionize sample metals placed behind a ring electrode. Both hyperbolic and cylindrical electrodes are successfully used for confinement of the ions. Trapped ions are detected either with a quadrupole mass spectrometer or with a photomultiplier for the measurement of laser-induced fluorescence. Metallic ions such as Ca⁺, Ba⁺, La⁺, Nd⁺, Tm⁺, Lu⁺, and Ta⁺ have been confined for the time range of several to 20 minutes in the presence of He buffer gas, and a doubly charged ion Ba²⁺ for several seconds. Some ions like Nd⁺, Lu⁺, Hf⁺, and Ta⁺ are found to be highly reactive with background gaseous molecules.