Progress ttrapping single indium ions for possible frequency reference

The $^1$S$_0 \rightarrow ^3$P$_0$ transition in the In$^+$ ion at 237 nm has a natural linewidth of 0.8 Hz and is a promising candidate for an optical frequency reference. Since this ``clock'' transition is J=0 $\rightarrow$ J=0, it lacks shifts from the electric quadrupole interaction, a leading systematic in some ions under investigation. This transisition coincides with the fourth harmonic of the 946 nm line available from already narrow-linewidth Nd:YAG lasers. We report recent developments in spectroscopy of single In$^+$ ions using a Paul-Staubel trap and a new frquency-quadrupled diode laser to excite the stronger $^1$S$_0 \rightarrow ^3$P$_1$ transition at 230 nm. We also propose comparisons between the indium ion frequency reference and other frequency references at the University of Washington.