  The semiclassical theory of laser cooling is applied for the analysis of
cooling of unbound atoms with the values of the ground and exited state angular
moments 1/2 in a one-dimensional nondissipative optical lattice. We show that
in the low-saturation limit with respect to the pumping field a qualitative
interpretation of the cooling mechanisms can be made by the consideration of
effective two-level system of the ground-state sublevels. It is clarified that
in the limit of weak Raman transitions the cooling mechanism is similar to the
Doppler mechanism, which is known in the theory of two-level atom. In the limit
of strong Raman transitions the cooling mechanism is similar to the known
Sisyphus mechanism. In the slow atom approximation the analytical expressions
for the coefficients of friction, spontaneous and induced diffusion are given,
and the kinetic temperature is estimated.
