Pei Ding

Surface plasmon resonance and field enhancement in #-shaped gold wires metamaterial

A #-shaped gold wires metamaterial is designed for surface enhanced Raman spectroscopy (SERS) and sensing. The tunability of surface plasmon resonance (SPR) excitations, hotspots distribution, localized field enhancement and sensitivity of the structure are investigated. In contrast to most metamaterial, the #-shaped structure exhibits two pronounced SPRs that are insensitive to the polarization of excitation light. Pure electromagnetic Raman enhancement factors of about 10(6) are achieved on the symmetrically distributed field hotspots. It is possible to break the usable wavelength range of conventional gold SERS substrates via higher order excitations of the #-shaped metamaterial. In addition, the sensitivity and the figure of merits are found to be comparable or even higher than those of conventional SERS substrates. All these factors together with the high reproducibility nature of metamaterial and its simple planer structure suggest that this structure is very promising for surface enhanced spectroscopy and sensing applications.

SPP-associated dual left-handed bands and field enhancement in metal-dielectric-metal metamaterial perforated by asymmetric cross hole arrays

Dual-band left-handed transmissions in the near infrared frequencies through the metal-dielectric-metal metamaterial perforated with an array of asymmetric cross holes are demonstrated. It is shown that the left-handed bands originate from the SPP-associated magnetic response excited by different polarized light and their frequencies can be tuned by the arms length or width of the cross-gaps. The structures are further optimized at 1.064 microm laser light excitation for elucidating the mechanism and possible application in surface enhanced Raman spectroscopy in sandwiched architectures. This study provides valuable information for the design of compact optical devices with dual left-handed bands in a single structure and may also pave the way toward stable and reproducible substrate design for surface enhanced Raman spectroscopy.

Theoretical investigation of a plasmonic substrate with multi-resonance for surface enhanced hyper-Raman scattering

Because of the unique selection rule, hyper-Raman scattering (HRS) can provide spectral information that linear Raman and infrared spectroscopy cannot obtain. However, the weak signal is the key bottleneck that restricts the application of HRS technique in study of the molecular structure, surface or interface behavior. Here, we theoretically design and investigate a kind of plasmonic substrate consisting of Ag nanorices for enhancing the HRS signal based on the electromagnetic enhancement mechanism. The Ag nanorice can excite multiple resonances at optical and near-infrared frequencies. By properly designing the structure parameters of Ag nanorice, multi- plasmon resonances with large electromagnetic field enhancements can be excited, when the “hot spots” locate on the same spatial positions and the resonance wavelengths match with the pump and the second-order Stokes beams, respectively. Assisted by the field enhancements resulting from the first- and second-longitudinal plasmon resonance of Ag nanorice, the enhancement factor of surface enhanced hyper-Raman scattering can reach as high as 5.08 × 109, meaning 9 orders of magnitude enhancement over the conventional HRS without the plasmonic substrate.