Ultracold negative ions for antimatter experiments

After the first production of cold antihydrogen by the ATHENA experiment, second-generation experiments are being performed and/or being set up with the aim of measuring the fundamental properties of this anti-atom. A challenge that all these activities have in common is the need for ultracold antihydrogen for precision measurements. One path towards this goal is the pre-cooling of antiprotons prior to recombination. Currently available cooling techniques for negatively charged particles allow cooling only to the temperature of the surrounding environment. A fast electronic transition in an atomic anion could be used to laser-cool an ensemble to microkelvin temperatures. These could sympathetically cool any species of negatively charged particles - from antiprotons to molecular anions - to ultracold temperatures. Until now, there are only three known atomic anions with electric-dipole transitions. We have been investigating the bound - bound electric-dipole transitions in Os^- and La^- by high-resolution laser spectroscopy to investigate their suitability for laser cooling. The principle of the method, its potential applications, as well as recent experimental results will be presented.