  We present the results of the light-shift calculations in the ns-states of
hydrogenicsystems in the presence of a weak laser field. This is done by means
of analytical calculations of the scalar dynamic polarizabilities (DP) of the
corresponding levels. In contrast to the usual technique, 1.e. by solving
certain inhomogeneous differential equation. As a result, we obtained for the
DP a closed analytical expression valid for all principal quantum numbers, n.
Within a framework of such an approach we succeeded both in retrieving the well
known results and finding several new ones, as well.Our interest is focused
mainly on the states with low n, n=1,2, since they are of particular
importance.Various analytical properties of the DP of such levels are discussed
in full details. Numerical values of light-shifts are computed for those
energies and intensities of the laser field that are used in the 1S-2S
experimental investigation of the muonium atom.
