Velocity Dependence of the ARP Force

The optical force on atoms from coherent momentum exchange using adiabatic rapid passage (ARP) has been shown to be much larger than the usual radiative force\footnote{X. Miao, Phys. Rev. A 75, 011402 (2007).}. To gauge its broader utility, we are measuring its velocity dependence, $F(v)$. We counterpropagate two beams from phase-locked lasers, perpendicular to an atomic beam, and measure the deflection of atoms out of the beam. The atomic velocity $v$ is simulated by oppositely detuning these lasers by $\pm \delta = \pm kv$ where $k \equiv 2\pi/\lambda$. We have been surprised to find that $F(v)$ is asymmetric about $v=0$, and are investigating a number of explanations for this observation. We further test the utility of the ARP force by measuring $F(v)$ over a range of interaction times.