Lattice Resonances and Local Field Enhancement in Array of Dielectric Dimers for Surface Enhanced Raman Spectroscopy.

In this paper, we propose the use of high refractive index dimers for the realization of a surface enhanced Raman spectroscopy substrate, with an average enhancement factor comparable to plasmonic structures. The use of low loss dielectric materials is favorable to metallic ones, because of their lower light absorption and consequently a much lower heating effect of the substrate. We combined two different mechanisms of field enhancement to overcome the main weakness of dielectric dimers: a low enhancement factor compared to the plasmonic ones. A first mechanisms is associated to surface lattice resonances. This generates a narrow-band high enhancement, which is exploited to enhance the excitation light. A second mechanism exploits the local field enhancement between the dimers' resonators, for the band where the molecule Raman emission spectrum is located. The fact that both field enhancements can be tuned by acting on separate geometric parameters, makes possible to optimize the design for many different molecules. The optimized structure and its performance is presented together with a discussion of the different enhancement mechanisms.