Experimental and theoretical investigation of waveguided plasmonic surface lattice resonances

Plasmonic nanostructures are good candidates for refractive index sensing applications through the surface plasmon resonance due to their strong dependence on the surrounding dielectric media. However, typically low quality-factor limits their application in sensing devices. To improve the quality-factor, we have experimentally and theoretically investigated two-dimensional gold nanoparticle gratings situated on top of a waveguide. The coupling between the localized surface plasmon and waveguide modes results in Fano-type resonances, with high quality-factors, very similar to plasmonic surface lattice resonances. By combining plasmonic surface lattice resonance and waveguide theory, we present a theoretical framework describing the structures. By immersing the fabricated samples in three different media we find a sensitivity of ∼50 nm/RIU and figure of merit of 8.9, and demonstrate good agreement with the theory presented. Further analysis show that the sensitivity is very dependent on the waveguide parameters, grating constant and the dielectric environment, and by tuning these parameters we obtain a theoretical sensitivity of 887 nm/RIU.publishedVersio

Error in predicting hydrosol backscattering from remotely sensed reflectance

Monte Carlo simulations are carried out to determine the error in the inversion of backscattering from remotely sensed reflectance when geometrical shape factors of the light field are assumed to be unity. The results show that error in backscattering inversion can vary from a 40% overestimation to a 20% underestimation and is dependent on the solar angle and the hydrosol constituents contributing to backscattering. The simulations also demonstrate that for chlorophyll concentrations ranging from 0.05 to 20 mg m⁻³ the most dramatic change in the geometrical shape factor occurs near 1.0 to 1.5 mg m⁻³ chlorophyll. The potential importance of bacteria in influencing the shape factor and the subsequent effect of bacteria on the retrieval of the backscattering from remote sensing reflectance are shown. Quartzlike material's strong impact on geometrical shape factors and errors of retrieval of backscattering at low chlorophyll concentrations are also demonstrated. Remote sensing reflectance inversion schemes must include information about the backscattering function to be successful

Optical scattering and backscattering by organic and inorganic particulates in U.S. coastal waters

We present the results of a study of optical scattering and backscattering of particulates for three coastal sites that represent a wide range of optical properties that are found in U.S. near-shore waters. The 6000 scattering and backscattering spectra collected for this study can be well approximated by a power-law function of wavelength. The power-law exponent for particulate scattering changes dramatically from site to site (and within each site) compared with particulate backscattering where all the spectra, except possibly the very clearest waters, cluster around a single wavelength power-law exponent of −0.94 . The particulate backscattering-to-scattering ratio (the backscattering ratio) displays a wide range in wavelength dependence. This result is not consistent with scattering models that describe the bulk composition of water as a uniform mix of homogeneous spherical particles with a Junge-like power-law distribution over all particle sizes. Simultaneous particulate organic matter (POM) and particulate inorganic matter (PIM) measurements are available for some of our optical measurements, and site-averaged POM and PIM mass-specific cross sections for scattering and backscattering can be derived. Cross sections for organic and inorganic material differ at each site, and the relative contribution of organic and inorganic material to scattering and backscattering depends differently at each site on the relative amount of material that is present

COMPARISON OF NUMERICAL-MODELS FOR COMPUTING UNDERWATER LIGHT FIELDS

Seven models for computing underwater radiances and irradiances by numerical solution of the radiative transfer equation are compared. The models are applied to the solution of several problems drawn from optical oceanography. The problems include highly absorbing and highly scattering waters, scattering by molecules and by particulates, stratified water, atmospheric effects, surface-wave effects, bottom effects, and Raman scattering. The models provide consistent output, with errors (resulting from Monte Carlo statistical fluctuations) in computed irradiances that are seldom larger, and are usually smaller, than the experimental errors made in measuring irradiances when using current oceanographic instrumentation. Computed radiances display somewhat larger errors