Measurement of the temperature of an ultracold ion source using time-dependent electric fields

Abstract

We report on a measurement of the characteristic temperature of an ultracold rubidium ion source, in which a cloud of laser-cooled atoms is converted to ions by photo-ionization. Extracted ion pulses are focused on a detector with a pulsed-field technique. The resulting experimental spot sizes are compared to particle-tracking simulations, from which a source temperature $T=(1\pm 2)$ mK and the corresponding transversal reduced emittance ${\epsilon }_r=7.9X10^{-9}$ m rad $\sqrt{\mathrm{eV}}$ are determined. We find that this result is likely limited by space charge forces even though the average number of ions per bunch is 0.022.

8 pages, 11 figures