  Within leading-order perturbation theory, the Casimir-Polder potential of a
ground-state atom placed within an arbitrary arrangement of dispersing and
absorbing linear bodies can be expressed in terms of the polarizability of the
atom and the scattering Green tensor of the body-assisted electromagnetic
field. Based on a Born series of the Green tensor, a systematic expansion of
the Casimir-Polder potential in powers of the susceptibilities of the bodies is
presented. The Born expansion is used to show how and under which conditions
the Casimir-Polder force can be related to microscopic many-atom van der Waals
forces, for which general expressions are presented. As an application, the
Casimir-Polder potentials of an atom near a dielectric ring and an
inhomogeneous dielectric half space are studied and explicit expressions are
presented that are valid up to second order in the susceptibility.
