Elastic scattering, absorption, and surface-enhanced Raman scattering by concentric spheres comprised of a metallic and a dielectric region

Elastic scattering by a small inhomogeneous sphere, comprised of two concentric spherical regions, may be abnormally low if the dielectric constant of the external medium is intermediate between those of the two regions. When one of these regions is a metal with a real negative dielectric constant, there may also be very large enhancement of the scattering due to excitation of a dipolar surface plasmon. For a sphere in which the metallic region is silver, the incident radiation can be tuned over a range of optical wavelengths to give a variation of ${10}^6$ in scattering cross section. Such objects may exhibit very large surface-enhanced Raman scattering with excitation profiles sharply dependent upon the relative thickness of the spherical shell.