Measurement of isotope shifts in Fe II

We describe absorption spectra of singly ionized iron (Fe II) obtained with a compact ion source and a high-resolution UV laser. Using a Nd:YAG laser ablation source and buffer gas cooling with room-temperature argon, Fe II ions are produced in a cold plasma. Grating spectroscopy is used to determine conditions favorable parameters providing good cooling and ion yield. This novel technique allows us to study the Fe II transition $a ^6D_9 \rightarrow z^6D^o_9$ with Doppler widths about 3 GHz, by measuring the absorption of a frequency-tripled pulse-amplified cw Ti:Sapphire laser. The isotope shift of this transition is important to the analysis of astronomical data on the cosmological evolution of the fine-structure constant $\alpha$ [1]. We will discus the design of the ion source and laser system, and present preliminary results. This study was funded by the National Science Foundation. \par \vspace{12 pt} \noindent [1] J.K Webb,M.T. Murphy, V.V. Flambaum, V.A. Dzuba, J.D. Barrow, C.W. Churchill, J.X. Prochaska, and A.M. Wolfe, Phys. Rev. Lett. \textbf{87}, 091301 (2001).