Resonance properties of thick plasmonic split ring resonators for sensing applications.

We investigate in detail the optical response of dense split ring resonator (SRR) arrays as a function of their thickness, for normally impinging light in the VIS-NIR spectral range. We find that, for sufficiently tall SRRs, several vertical Fabry-Perot resonances can be excited, which may interact with the well-known horizontal SRR resonant paths. Furthermore, we analyze the possibility to exploit these nanostructures to detect bio-chemical quantities. In particular, we find that the coexistence of vertical and horizontal resonances yields an increased sensitivity. Well ordered, large arrays of thick SRRs are obtained by exploiting a fabrication process based on X-Ray Lithography. A very good agreement is found between numerical and measured transmittances. A preliminary detection test evidences the potential of this geometry as a sensing platform.