Optical Phase Coherence in the Adiabatic Rapid Passage (ARP) Force

The huge optical force on atoms implemented using ARP results from coherent exchange of momentum between atoms and the light field. This is done with counterpropagating beams of chirped, pulsed light that alternately produce absorption followed by stimulated emission, and has been demonstrated for atoms at rest\footnote{X. Miao, Phys. Rev. A 75, 011402 (2007).}. How does the ARP force depend on atomic velocities $v_a$? Atomic motion in the lab frame corresponds to Doppler-shifted frequencies in the atomic frame, so we use oppositely detuned laser beams to simulate $v_a$. For large $v_a$ this uses two different lasers, but the coherent momentum exchange requires phase locking them\footnote{J. Elgin, Ph.D Thesis, Stony Brook University, 2015.}. This has been implemented and the first results show that the force is nearly constant at low $v_a$ but decreases at higher $v_a$. For an ARP frequency sweep range of $\pm \, \delta_0$, one intuitively expects a range of $v_a$ between 1/4 and 1/2 of $\pm \, \delta_0/k$, and our initial measurements corroborate this. Our new tools enable further exploration of the dependence of the ARP force on $v_a$ as well as the role of phase noise that can be inserted experimentally.