Surface-plasmon enhancement of Brillouin light scattering from gold-nanodisk arrays on glass

摘要

Enhancement of Brillouin light scattering (BLS) at the wavelength of 532 nm was observed from Rayleigh-like and Sezawa-like acoustic modes of alkaline-earth boro-aluminosilicate glass covered with periodic arrays of gold nanodisks. This enhancement is attributed to mediation of surface plasmons of the nanodisks. For nanodisks with diameters of 71 nm to 90 nm, heights of 30 nm, and periodicity of 100 nm, the maximum measured surface-plasmon enhancement of BLS intensity was, respectively, ～ 2.4 and ～ 5.6 for Rayleigh-like and Sezawa-like modes, relative to the intensity from a gold film with the same fractional coverage area but without surface-plasmon coupling. The maximum for the Rayleigh-like modes occurs with the smallest-diameter nanodisks, and that for the Sezawa-like modes occurs with the largest-diameter nanodisks. The angular dependence is relatively broad. Calculations employing the discrete dipole approximation were used to predict the electric-field intensities in the gold disks and nearby glass as a function of nanodisk diameter. The average calculated intensity at the top surface of the gold increases with decreasing diameter, consistent with the experimental results for Rayleigh-like modes and the expectation that surface ripple is the dominant scattering mechanism for such modes. The results of this study suggest that nanodisk arrays can provide a platform for practical implementation of surface-enhanced BLS analogous to other surface-enhanced spectroscopies, and suggest the additional possibility of substantially extending the range of wave numbers in BLS through plasmonic-crystal band folding.