| In this thesis we use extensions of Mie theory to study electromagnetic enhancement factors associated with surface enhanced Raman scattering (SERS) from molecules adsorbed onto metal spheres, metal sphere dimers, array structures comprised of metal spheres, and micron sized dielectric spheres and we compare the results from the more rigorous dipole re-radiation (DR) expression for Raman enhancement with the commonly used plane-wave (PW) enhancement formula. In the PW expression, the enhancement is considered to be equal to the product of the squares of the local electric fields, |E loc(o)|2|Eloc (o')|2 or |Eloc(o)| 4 for zero Stokes shift, obtained from plane wave Mie scattering. In the DR calculation, the induced dipole in a molecule that is located at the surface of one of the spheres serves as a dipole source at the Stokes-shifted frequency that scatters from the particle structure to define an overall enhancement factor. When multiple spheres are considered, the DR and PW calculations are based on the T-matrix method for determining optical scattering from multiple spheres. The errors associated with employing the PW are small for small isolated spheres, but can become lager when more spheres are considered, or the spheres become large with respect to the wavelength of radiation. The magnitude of the error is also highly dependent upon the location of the detector in the far-field. When the arrangement is a backscattering configuration the errors associated with PW are small compared to DR. However, other detector locations lead to much larger errors. This demonstrates the importance of including DR effects in the interpretation of SERS experiments. |
