Calculations on the steady-state distribution of atoms cooled in three
coplanar laser beams are presented. For this three-beam configuration
, the achievements of Sisyphus cooling are independent of fluctuations
in the relative time phases between the beams. The atomic motion is q
uantized and the steady-state solution of the density-matrix equations
is found within a secular approximation. We obtain a minimum width of
the cooled momentum distributions on the order of six photon momenta.