Plasmonic optical antennas excited by resonant guided mode for SERS applications

We report a numerical study on the frequency property of a system composed of an optical antenna array placed on the surface of a dielectric grating. Such a periodic structure is designed for Raman spectroscopy application because of its advantages over the conventional rough-surface based surface enhanced Raman spectroscopy: the position of the high field intensity and the exact field magnitude is well controlled by the design, and the constructive interference from the elements placed in periodic array may form a collective resonance and provide a further enhancement to the field intensity. By integrating and weakly coupling the guided mode resonance (GMR) of a dielectric grating with optical nano-antennas made of plasmonic materials that are also field-enhancing devices, it provides a further enhanced local field around the antenna. We specifically studied the behavior of the device under oblique incidence, and show that multiple resonant peaks are observed in the spectrum. The application of the device in a Raman process is discussed in details.