Theoretical model of an optical setup for microwave sensing

Light scattering by three parallel infinite cylinders is proposed as a possible model of situations in which evanescent waves are used to probe scattering objects in the near field. In elaborating the model the coupling effects between the scatterer are taken into account by using the Addition Translational Theorem. The multiple reflection process is minimized by using an incident field which is a moderately focused, off-axis localized Gaussian beam. The parameters of the beam are such that a optical resonance which is also denominated "Morphology Dependent Resonance" (MDR) is excited in one of the cylinders (pump). The setup consists of three cylinder of which one is dielectric and the other two are metallic. Once the a resonant field is present at the pump cylinder the external medium resonant field generated is an evanescent radial field. The same field can be used as a tool to probe the other cylinder properties by collecting the scattering signal generated by it. Having based the principals on the extended Mie theory we search for the proper limits and arrangement of the parameters to model experiments that make rise of evanescent wave scattering commonly found in optical configurations. This scheme is proposed as a microwave sensor, since in both of the metallic cylinders a current is induced due to the microwave radiation and by mutual inductance an attractive force between the two cylinders changes the distance between them. This change is observed by the scattering signal since the optical field is highly sensitive in the region of nanometers.