The spectra of neutral and ionized rare earth elements have been receiving renewed attention from laboratory spectroscopists during recent years. These efforts have been motivated by data needs of the astrophysics community and lighting research community.
Rare earth elements have rich visible spectra due to their open f-shells. Many rare earth lines can be observed in the spectra of metal-poor Galactic halo stars using large ground based telescopes. The old metal-poor halo stars provide a fossil record of the chemical make-up of our Galaxy when it, and the Universe, was very young. Heavy elements, including the rare earths, are synthesized via neutron or n-capture processes. Some heavy elements and isotopes are produced primarily or exclusively by the rapid (or r-)process and others are produced by the slow (or s-)process. A few metal-poor halo stars have nearly pure r-process abundance patterns. Studies of these stellar abundance patterns are leading to a better understanding of the r-process, of the Galactic chemical evolution, and some constraints on the age of the Universe [e.g. 1].
The rich visible spectra of rare earth elements makes them ideal as additives in modern Metal Halide High Intensity Discharge (MH-HID) lamps. MH-HID lamps are widely used today, and are being studied for continued development, because of their superior color and efficacy [e.g. 2]. MH-HID lamps are high pressure (many bar) mercury arc lamps with metal halide additives such as rare earth iodides. These additive salts evaporate at arc tube temperatures, the salt molecules dissociate in the arc, and the metal atoms and ions radiate strongly from the arc core to produce high quality white light. Basic spectroscopic data are needed for modeling and diagnosing MH-HID lamps.
Our primary interest is the continued development and application of advanced techniques for measuring atomic transition probabilities. We use laser induced fluorescence (LIF) measurements to determine radiative lifetimes, and a Fourier transform spectrometer (FTS) to measure emission branching fractions. The combination of these radiative lifetime and branching fraction data yields large set of absolute, atomic transition probabilities with good precision and accuracy. Recent examples will be discussed [e.g. 3]. Ongoing efforts to understand and control systematic errors in these measurements while maintaining high productivity will be discussed.
In spectra where hypefine structure (hfs) and/or isotope shifts (IS) are large and important from an astrophysical perspective, it has often been possible to extract the needed hfs/IS parameters from FTS data. Although such FTS measurements of hfs/IS data are not as accurate as laser or laser/radio frequency measurements, they are far faster and cheaper. Numerous comparisons to more accurate hfs/IS data reveal that parameters from FTS data are satisfactory for synthesizing stellar spectra.
Efforts to extend this work deeper into the UV and vacuum UV will be discussed.

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