Periodic adiabatic rapid passage from counterpropagating light pulses is used in a parameter domain outside of the conventionally expected successful range to produce large optical forces on atoms by coherent control of the momentum exchange between the light and atoms. Both the magnitude and velocity range are much larger than those of the usual radiative force. We observed the force on metastable He atoms by the deflection of the atomic beam with periodic pulse sequences. We have also been able to map out the force magnitude in the two-dimensional parameter space of peak Rabi frequency and sweep range, and we find qualitative agreement with our model.

The bichromatic force has been used to both slow and collimate a beam of metastable 2(3)S He atoms (He*). The collimation capture range is an extraordinary +/-85 m/s corresponding to approximately 0.18 radians from our source. Both slowing and collimation were accomplished in the unprecedented short distance of approximately 5 cm each. The overall brightness increase is x3200, and there is potential for considerably more.

To apply the adiabatic rapid passage process repetitively ͓T. Lu, X. Miao, and H. Metcalf, Phys. Rev. A 71, 061405͑R͒ ͑2005͔͒, the nonadiabatic transition probability of a two-level atom subject to chirped light pulses over a finite period of time needs to be calculated. Using a unitary first-order perturbation method in the rotating adiabatic frame, an approximate formula has been derived for such transition probabilities in the entire parameter space of the pulses.

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