Velocity-selective magnetic-resonance laser cooling

We describe a new sub-Doppler cooling scheme that cools atoms to nonzero velocity ${\mathit{v}}_{\mathit{r}}$. The atomic motion in a combined optical standing wave and constant magnetic field induces a velocity-selective magnetic resonance that produces strong cooling for negative laser detuning to ${\mathit{v}}_{\mathit{r}}$=${\mathrm{\omega }}_{\mathit{Z}}$/2k, with ${\mathrm{\omega }}_{\mathit{Z}}$ the Larmor frequency. In a one-dimensinal optical molasses transverse to a thermal Rb beam we observe the bunching of the atoms into two peaks corresponding to ±${\mathit{v}}_{\mathit{r}}$. We present a quantitative comparison between our theory and experiment and suggest some applications.