  Dispersion forces such as van der Waals forces between two microscopic
particles, the Casimir--Polder forces between a particle and a macroscopic
object or the Casimir force between two dielectric objects are well studied in
vacuum. However, in realistic situations the interacting objects are often
embedded in an environmental medium. Such a solvent influences the induced
dipole interaction. With the framework of macroscopic quantum electrodynamics,
these interactions are mediated via an exchange of virtual photons. Via this
method the impact of a homogeneous solvent medium can be expressed as
local-field corrections leading to excess polarisabilities which have
previously been derived for hard boundary conditions. In order to develop a
more realistic description, we investigate on a one-dimensional analog system
illustrating the influence of a continuous dielectric profile.
