Fully analytical description of adiabatic compression in dissipative polaritonic structures

We have theoretically modeled and experimentally fabricated a nanoscale adiabatic (conical) metallic structure that is suitable for high-resolution Raman spectroscopy. We report on a fully complex analytical description of the adiabatic compression phenomenon which is investigated in terms of both geometrical and optical parameters. An explicit analytical description of adiabatic compression is provided together with the physical role played by the complex effective refractive index of the polaritonic adiabatic mode. In particular, we have examined the role of absorption on the field enhancement. Finally, we demonstrate how such a device can experimentally enhance the Raman signal coming from nanosamples such as a bead of SiO _x and a monolayer of benzenethiol.