Laser Manipulation of Atoms
Photons from a near-resonant laser will be absorbed and re-emitted by an atom. Each event gives a recoil in the amount of the photon's momentum. Since the emission pattern is symmetric, the emitted photons contribute no net momentum change. The atoms will feel a net force from the laser ("light pressure").
The single-photon recoil for Cs is3.5 mm per second. But since it can scatter more than 10,000,000 photons per second, the atoms can feel an acceleration as large as 50,000 meters/second or about 5000 g's.
A University of Colorado Interactive Java Applet that demonstrates optical molasses.