A Study of the Velocity Dependence of the ARP Force

The huge optical force enabled by multiple adiabatic rapid passage (ARP) sequences results from coherent exchange of momentum between atoms and light at a high repetition rate.\footnote{H.Metcalf, Rev.Mod.Phys. \textbf{89} 041001 (2017).} We have been studying its dependence on atomic velocity F$_{ARP}$($\upsilon$). We use counter-propagating beams from phase-locked lasers, perpendicular to an atomic beam, and measure the deflection of atoms out of the beam. We simulate the Doppler shifts of a transverse atomic velocity by oppositely detuning the frequency of the two light beams. The overall features of F$_{ARP}$($\upsilon$) in our experiments match well with our simulations over a wide range of atomic velocities. However, some detailed structures of F$_{ARP}$($\upsilon$) remain to be explained. In order to gain more insight into these structures, we have measured F$_{ARP}$($\upsilon$) over a range of interaction times and are also working on varying the repetition rate of momentum exchange to ameliorate the effects of sweep imperfections.