Intrinsic Fano Interference of Localized Plasmons in Pd Nanoparticles

Palladium (Pd) nanoparticles exhibit broad optical resonances that have been assigned to so-called localized surface plasmons (LSPs). The resonance's energy varies with particle shape in a similar fashion as is well known for LSPs in gold and silver nanoparticles, but the line-shape is always anomalously asymmetric. We here show that this effect is due to an intrinsic Fano interference caused by the coupling between the plasmon response and a structureless background originating from interband transitions. The conclusions are supported by experimental and numerical simulation data of Pd particles of different shape and phenomenologically analyzed in terms of the point dipole polarizability of spheroids. The latter analysis indicates that the degree of Fano asymmetry is simply linearly proportional to the imaginary part of the interband contribution to the metal dielectric function

Plasmon-Interband Coupling in Nickel Nanoantennas

Plasmonic excitations are usually attributed to the free electron response at visible frequencies in the classic plasmonic metals Au and Ag. However, the vast majority of metals exhibit spectrally localized interband transitions or broad interband transition backgrounds in the energy range of interest for nanoplasmonics. Nevertheless, the interaction of interband transitions with localized plasmons in optical nanoantennas has hitherto received relatively little attention, probably because interband transitions are regarded as highly unwanted due to their strong damping effect on the localized plasmons. However, with an increasing number of metals (beyond Au and Ag) being considered for nanoplasmonic applications such as hydrogen sensing (Pd), UV-SERS (Al), or magnetoplasmonics (Ni, Fe, Co), a deeper conceptual understanding of the interactions between a localized plasmon mode and an interband transition is very important. Here, as a generic example, we examine the interaction of a localized (in energy space) interband transition with spectrally tunable localized plasmonic excitations and unearth the underlying physics in a phenomenological approach for the case of Ni disk nanoantennas. We find that plasmon interband interactions can be understood in the classical picture of two coupled harmonic oscillators, exhibiting the typical energy anticrossing fingerprint of a coupled system approaching the strong-coupling regime

Optical response of supported gold nanodisks

It is shown that the ellipsometric spectra of short range ordered planar arrays of gold nanodisks supported on glass substrates can be described by modeling the nanostructured arrays as uniaxial homogeneous layers with dielectric functions of the Lorentz type. However, appreciable deviations from experimental data are observed in calculated spectra of irradiance measurements. A qualitative and quantitative description of all measured spectra is obtained with a uniaxial effective medium dielectric function in which the nanodisks are modeled as oblate spheroids. Dynamic depolarization factors in the long-wavelength approximation and interaction with the substrate are considered. Similar results are obtained calculating the optical spectra using the island-film theory. Nevertheless, a small in-plane anisotropy and quadrupolar coupling effects reveal a very complex optical response of the nanostructured arrays

Magnetoplasmonic design rules for active magneto-optics

Light polarization rotators and non-reciprocal optical isolators are essential building blocks in photonics technology. These macroscopic passive devices are commonly based on magneto-optical Faraday and Kerr polarization rotation. Magnetoplasmonics - the combination of magnetism and plasmonics - is a promising route to bring these devices to the nanoscale. We introduce design rules for highly tunable active magnetoplasmonic elements in which we can tailor the amplitude and sign of the Kerr response over a broad spectral range

Designer Magnetoplasmonics with Nickel Nanoferromagnets

We introduce a new perspective on magnetoplasmonics in nickel nanoferromagnets by exploiting the phase tunability of the optical polarizability due to localized surface plasmons and simultaneous magneto-optical activity. We demonstrate how the concerted action of nanoplasmonics and magnetization can manipulate the sign of rotation of the reflected light’s polarization (i.e., to produce Kerr rotation reversal) in ferromagnetic nanomaterials and, further, how this effect can be dynamically controlled and employed to devise conceptually new schemes for biochemosensing. © 2011 American Chemical Society.A.D. and Z.P. acknowledge support from the Swedish Research Council and Swedish Foundation for Strategic Research (Framework program Functional Electromagnetic Metamaterials, project RMA08). J.Å. acknowledges support from the Swedish Research Council, the Swedish Foundation for Strategic Research (Future Research Leader Programme), and the G€oran Gustafsson Foundation. J.Å. is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation. V.B. acknowledges the G€oran Gustafsson Foundation and the Blanceflor Boncompagni-Ludovisi Foundation. P.V. acknowledges funding from the Basque Government through the ETORGAI Program, Project No. ER- 2010/00032 and Program No. PI2009-17, the Spanish Ministry of Science and Education under Projects No. CSD2006-53 and No. MAT2009-07980. J.N. acknowledges funding for the Generalitat de Catalunya and the Spanish Ministry of Science and Education through No. 2009-SGR-1292 and No. MAT2010-20616-C02 projects.Peer Reviewe

Unidirectional ultracompact optical nanoantennas

We report on a dramatic directionality effect in a simple and ultracompact optical nanoantenna consisting of a pair of interacting plasmonic nanoparticles. We found that the emission from a dipole source positioned close to one of the particles in the pair exhibits an essentially unidirectional radiation pattern for emission wavelengths close to the antiphase hybridized plasmon. We analyze this unique effect in terms of radiation, reception, and reciprocity concepts using electrodynamics simulations and dipole analysis. A forward-backward directionality of similar to 18 dB at 665 nm is obtained for a nanoantenna that consists of two 90 nm wide and 20 nm thick gold nanodisks separated by a 10 nm gap

Highly directional bottom-up 3D nanoantenna for visible light

Controlling light at the nanoscale is of fundamental importance and is essential for applications ranging from optical sensing and metrology to information processing, communications, and quantum optics. Considerable efforts are currently directed towards optical nanoantennas that directionally convert light into strongly localized energy and vice versa. Here we present highly directional 3D nanoantenna operating with visible light. We demonstrate a simple bottom-up approach to produce macroscopic arrays of such nanoantennas and present a way to address their functionality via interaction with quantum dots (QDs), properly embedded in the structure of the nanoantenna. The ease and accessibility of this structurally robust optical antenna device prompts its use as an affordable test bed for concepts in nano-optics and nanophotonics applications

Optical Forces in Plasmonic Nanoparticle Dimers

We present calculations of the optical forces between two metal nanospheres forming a hybridized plasmonic chiller. We consider homo- and heterodimers and investigate different plane wave illumination configurations. The forces between the particles are calculated using kill Mie theory combined with the Maxwell stress tensor (MST) formalism, as well as by approximate methods, such as the Lorentz force (LF) approach taken in the dipole limit and calculations based on an optical potential. We show that the simplified calculation schemes can lead to serious errors in the case of strongly interacting particles and low damping. In particular, we find that equilibrium configurations, corresponding to vanishing optical forces, only are possible for homodimers illuminated in the end-fire configuration and for heterodimers, although multipolar effects and clamping radically reduce the repulsive interactions in the latter case