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We investigate the generation of THz pulses when arrays of silver nanoparticles are irradiated by femtosecond laser pulses, providing the first reproducible experimental evidence in support of recent theoretical predictions of such an effect. We assess our results in the context of a model where photoelectrons are produced by plasmon-mediated multiphoton excitation, and THz radiation is generated via the acceleration of the ejected electrons by ponderomotive forces arising from the inhomogeneous plasmon field. By exploring the dependence of the THz emission on the femtosecond pulse intensity and as a function of metal nanoparticle morphology, and by comparing measurements to numerical modeling, we are able to verify the role of the particle plasmon mode in this process.

We present results from composite plasmonic nanostructures designed to achieve the cascaded enhancement of electromagnetic fields at optical frequencies. Our structures comprise a small metallic nanodisc suspended above a larger disk. We probe the optical properties of these structures by coating them with a layer of a visible-light fluorophore and observing fluorescence signals with the help of scanning confocal microscopy. A 43 +/- 5-fold increase in the far-field fluorescence signal has been observed for two-tier composite nanostructures, when compared to the signal obtained from individual nanodiscs. Our results offer the prospect of using such nanostructures for field concentration, optical manipulation of nanoobjects, chemical and biological sensing.

A comparison is presented of a number of simulation techniques that are used to compute the scattering of electromagnetic radiation by metallic nanostructures. The simulation techniques considered here are Mie theory, the T-Matrix null-field method, the discrete-dipole approximation, the finite-element method and the finite-difference time-domain method. The suitability of each technique is compared in terms of the accuracy, computation time and the range of geometries to which it can be applied. Using each technique, we perform example calculations by simulating the optical response of an 80 nm diameter Au sphere in vacuum. Our main conclusions are summarised in tabulated form, so that the findings presented in this article may serve as a useful reference guide to those looking for suitable numerical tools to model the optical response of metallic nanostructures. [ABSTRACT FROM AUTHOR]

We present results of numerical simulations for structures comprised of metallo-dielectric layers in which the metal layers are perforated with non-diffracting arrays of subwavelength holes, structures that are similar to the 'fishnet' structures being studied as electromagnetic metamaterials. We find for visible frequencies that such structures exhibit a stop-band in transmittance across a broad frequency range, which arises through interactions between two distinctly different types of resonant mode. Using numerical (finite element) modelling to characterise the optical response, we identify strong coupling between Fabry-Perot resonant cavity modes within the multilayer structure and localised surface-plasmon resonances associated with the nanoholes. Our simulations show that the spectral position and width of the stop-band that occurs within the visible frequency range can be tuned by varying both the cavity spacing and the geometry of the nanohole array. [ABSTRACT FROM AUTHOR]

A nanostructured surface in the form of a bi-grating is shown to efficiently couple surface plasmon polaritons to free-space radiation in the visible part of the spectrum. Coupling was achieved for all propagation directions of the surface mode and the efficiency found to be independent of the propagation direction, taking a mean value of 60% for the structure examined. The consequences of the findings for emissive devices that make use of surface plasmons are discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Weshow that dye-doped polymers open an interesting route to controllinglight at the nanoscale. Just as for the much better known metal-basedplasmonic systems, propagating and localized modes are possible. Weshow that the attractive features offered by plasmonics, specificallyenhanced optical fields and subwavelength field confinement, are alsoavailable with these materials. They thus open a new opportunity innanophotonics in which fabrication and functionality might be achievedby harnessing molecular and supramolecular chemistry. [ABSTRACT FROM AUTHOR]