  The local-field (LF) problem of a finite-size dipole emit- ter radiating
inside a lossy inhomogeneous structure is a long-standing and challenging
quantum optical problem, and it now is becoming more important due to rapid
advances in solid-state fabrication technologies. Here we introduce a simple
and accurate quasi-normal mode (QNM) technique to solve this problem analyti-
cally by separating the scattering problem into contribu- tions from the QNM
and an image dipole. Using a real- cavity model to describe an artificial atom
inside a lossy and dispersive gold nanorod, we show when the contri- bution of
the QNM to LFs will dominate over the homo- geneous contribution. We also show
how to accurately describe surface scattering for real cavities that are close
to the metal interface and explore regimes when the surface scattering
dominates. Our results offer an intui- tive picture of the underlying physics
for the LF problem and facilitate the understanding of novel photon sources
within lossy structures.
