RESUMO
We illustrate the important trade-off between far-field scattering effects, which have the potential to provide increased optical path length over broad bands, and parasitic absorption due to the excitation of localized surface plasmon resonances in metal nanoparticle arrays. Via detailed comparison of photocurrent enhancements given by Au, Ag and Al nanostructures on thin-film GaAs devices we reveal that parasitic losses can be mitigated through a careful choice of scattering medium. Absorption at the plasmon resonance in Au and Ag structures occurs in the visible spectrum, impairing device performance. In contrast, exploiting Al nanoparticle arrays results in a blue shift of the resonance, enabling the first demonstration of truly broadband plasmon enhanced photocurrent and a 22% integrated efficiency enhancement.
RESUMO
We present the numerical and experimental demonstration of plasmonic Bragg filters and resonators inside metal-insulator-metal (MIM) waveguides. The presented filters and resonators are fabricated using standard top down lithography methods. The optical bandgap of the integrated Bragg filters is experimentally observed and its optical properties are investigated as a function of the grating pitch and the number of grating periods. Transmission filters based on a nanocavity resonance were measured, obtaining Q-factors above 30. Tuning of the cavity wavelength was experimentally achieved by varying the cavity length.
RESUMO
We present a new electromagnetic phenomenon-the asymmetric second-harmonic generation from planar chiral structures. The effect consists in distinguishing the handedness of a chiral material by rotating the sample in an experiment involving solely linearly polarized light. This phenomenon originates in the surface plasmon resonance of chiral gold nanostructures, where homodyne interference of anisotropic and chiral electric and/or magnetic multipoles appears to play an important role.
RESUMO
In a statewide survey of 856 Iowa municipal drinking water supplies in 1986-1987 the Rathbun rural water system was found to contain elevated levels of triazine herbicides. Rates of low birth weight, prematurity, and intrauterine growth retardation (IUGR) in live singleton births during the period 1984-1990 by women living in 13 communities served by the Rathbun water system were compared to other communities of similar size in the same Iowa counties. The Rathbun communities had a greater risk of IUGR than southern Iowa communities with other surface sources of drinking water (relative risk = 1.8; 95% CI = 1.3, 2.7). Multiple linear regression analyses revealed that levels of the herbicides atrazine, metolachlor, and cyanzinc were each significant predictors of community IUGR rates in southern Iowa after controlling for several potentially confounding factors including maternal smoking and socioeconomic variables. The association with IUGR was strongest for atrazine, but all three herbicides were intercorrelated and the independent contributions of each to IUGR risk could not be determined. We conclude that communities in southern Iowa with drinking water supplies contaminated with herbicides have elevated rates of IUGR compared to neighboring communities with different water supplies. Because of the limitations of the ecologic design of this study, including aggregate rather than individual measures of exposure and limited ability to control for confounding factors related to source of drinking water and risk of IUGR, a strong causal relationship between any specific water contaminant and risk of IUGR cannot yet be inferred. The association between the water supplied to the Rathbun communities and the increased risk of IUGR should be considered a preliminary finding that needs to be verified by more detailed epidemiologic studies.
