Coherent exchange of momentum between atoms and light

We have demonstrated that coherent control of the momentum exchange between a light field and atoms can be implemented in frequency-modulated light. The optical parameters are chosen to drive the atoms between ground and excited states by adiabatic rapid passage in counterpropagating modulated light beams. We apply the optical force transversely to a thermal atomic beam, and the deflection provides a measure of the force. The modulation period is 2π/ω_s τ, and each half-cycle exchanges momentum 2hk, so the resulting force is much greater than the ordinary radiative force. Moreover, the velocity range of the force in such a light field is much greater than that of the radiative force. This constitutes another example of the huge range of capabilities of optical forces in non-monochromatic light.