A diode laser system for sideband cooling of Sr$^+$

Sideband cooling is performed on the 5S$_{1/2}$ to 4D$_{5/2}$ line of Sr$^+$ in an RF Paul trap using a diode laser system in which the linewidth is reduced by optical feedback and the frequency is stabilized to the ion. The diode laser system uses optical feedback from a filter cavity to narrow the linewidth of an external cavity diode laser to $\leq 30$ kHz.\footnote{J. Labaziewicz, P. Richerme, K. R. Brown, I. L. Chuang, and K.Hayasaka, ``Compact, filtered diode laser system for precision spectroscopy,'' Opt. Lett. 32, 572-574 (2007)} The frequencies of the sideband cooling (674 nm) and Doppler cooling (422 nm) lasers are stabilized by performing a shelving experiment on the 5S$_{1/2}$ to 4D$_{5/2}$ carrier transition. This stabilization feedback is included in the pulse sequence used for sideband cooling. Using this scheme, the axial motion is sideband cooled to an average quanta $\langle n_z \rangle \leq 0.11$ without stabilizing the lasers to a high-finesse cavity.