  We take a closer look at the fundamental Casimir-Polder interaction between
quantum particles and dispersive dielectric surfaces with surface polariton or
plasmon resonances. Linear response theory shows that in the near field, van
der Waals, regime the free energy shift of a particle contains a thermal
component that depends exclusively on the population/excitation of the
evanescent surface polariton/plasmon modes. Our work makes evident the link
between particle surface interaction and near field thermal emission and
demonstrates how this can be used to engineer Casimir-Polder forces. We also
examine how the exotic effects of surface waves are washed out as the distance
from the surface increases. In the case of molecules or excited state atoms,
far field approximations result in a classical dipole-dipole interaction which
depends on the surface reflectivity and the mean number of photons at the
frequency of the atomic/molecular transition. Finally we present numerical
results for the CP interaction between Cs atoms and various dielectric surfaces
with a single polariton resonance and discuss the implications of temperature
and retardation effects for specific spectroscopic experiments.
