Velocity Dependence of the Optical Force Produced by Adiabatic Rapid Passage

Adiabatic Rapid Passage (ARP) produces optical forces much larger than the ordinary radiative force, and is thought to work best when $\Omega_0 \sim \delta_0 \gg \omega_m \gg \gamma$, where $\Omega_0, ~ \delta_0,~ \omega_m, {\rm ~and~} \gamma$ are the Rabi frequency, sweep range, sweep rate, and natural decay rate respectively. We have observed strongly enhanced ARP forces on the 2$^3$S$_1 \rightarrow$ 2$^3$P$_2$ transition of He outside of this parameter range with our improved apparatus described previously.\footnote{D. Stack et al., Bull. Am. Phys. Soc. {\bf 56}, 153 (2011)} Our independent counter-propagating, chirped pulses allow greater freedom in the choice of relative beam parameters so we can detune the beams to simulate atomic motion. We will present our new data on the velocity dependence of the ARP force and compare these with our calculations.\footnote{D. Stack et al., Phys. Rev. A, {\bf 84}, 013420 (2011)}