Theoretical and experimental studies on the properties of the radiatio
n force acting on two-level atoms in a bichromatic standing light wave
are reported. It is shown that on an atom at rest a rectified gradien
t force is exerted having a great magnitude (almost-equal-to 4hkgammaB
AR observed in the experiment) in combination with a macroscopic spati
al period (almost-equal-to 10 cm). The dependence of the force on the
atomic velocity is investigated.