Titanium dioxide (TiO2) displays photocatalytic behavior under near-ultraviolet (UV) illumination. In another scientific field, it is well understood that the excitation of localized plasmon polaritons on the surface of silver (Ag) nanoparticles (NPs) causes a tremendous increase of the near-field amplitude at well-defined wavelengths in the near UV. The exact resonance wavelength depends on the shape and the dielectric environment of the NPs. We expected that the photocatalytic behavior of TiO2 would be greatly boosted if it gets assisted by the enhanced near-field amplitudes of localized surface plasmon (LSP). Here we show that this is true indeed. We named this new phenomenon "plasmonic photocatalysis". The key to enable plasmonic photocatalysis is to deposit TiO2 on a NP comprising an Ag core covered with a silica (SiO2) shell to prevent oxidation of Ag by direct contact with TiO2. The most appropriate diameter for Ag NPs and thickness for the SiO2 shell giving rise to LSP in the near UV were estimated from Mie scattering theory. Upon implementing a device that took these design considerations into account, the measured photocatalytic activity under near UV illumination of such a plasmonic photocatalyst, monitored by decomposition of methylene blue, was enhanced by a factor of 7. The enhancement of the photocatalytic activity increases with a decreased thickness of the SiO2 shell. The plasmonic photocatalysis will be of use as a high performance photocatalyst in nearly all current applications but will be of particular importance for applications in locations of minimal light exposure.

We experimentally demonstrate a three-dimensional chiral optical metamaterial that exhibits an asymmetric transmission for forwardly and backwardly propagating linearly polarized light. The observation of this novel effect requires a metamaterial composed of three-dimensional chiral metaatoms without any rotational symmetry. Our analysis is supported by a systematic investigation of the transmission matrices for arbitrarily complex, lossy media that allows deriving a simple criterion for asymmetric transmission in an arbitrary polarization base. Contrary to physical intuition, in general the polarization eigenstates in such three-dimensional and low-symmetry metamaterials do not obey fixed relations and the associated transmission matrices cannot be symmetrized.PACS numbers: XX.XX.XX During the past several years optical metamaterials (MMs) have attracted an enormous interest since they promise to allow for a manipulation of light propagation to a seemingly arbitrary extent. MMs are usually obtained by assembling sub-wavelength unit cell structures called metaatoms. Initial studies on MMs were based on rather simple and highly symmetric metaatoms [1][2][3]. Recently, more and more sophisticated structures were explored in order to achieve customized functionalities like, e.g. a negative refractive index due to chirality [4-6]. Also, a large variety of plasmonic metaatoms were investigated that evoke a huge polarization rotation like gammadions, omega shaped particles or helices [7][8][9]. Studying the characteristics of light propagation in such low-symmetry MMs also revealed unexpected phenomena like asymmetric transmission for circularly polarized light [10][11][12]. Although at first sight this effect of nonreciprocal transmission, to date not observed for linearly polarized light, is counterintuitive, it does not violate Lorentz' reciprocity theorem. This asymmetric transmission of circularly polarized light was demonstrated at so-called planar chiral MMs. Such MMs are composed of metaatoms without structural variation in the principal propagation direction. They preserve symmetry in this direction and are only chiral in the two-dimensional space [13]; thus, strictly speaking, they are intrinsically achiral in three dimensions since the mirror image of a structure is congruent with the structure itself if operated from the backside. The remaining mirroring plane is perpendicular to the propagation direction.In this Letter we theoretically and experimentally demonstrate a novel MM design which breaks the latter symmetry. For the first time our approach reveals that the very structures exhibit asymmetric transmission for linearly polarized light. We emphasize that also in this case the reciprocity theorem is not violated since only reciprocal materials are involved.Prior to any further considerations we concisely discuss the effect of a potential MM substrate that is, after all, in most cases required for fabricating planar MMs. Generally speaking, just this supporting substrate breaks the mirror symmetry for ...

By relying on an advanced Jones calculus we analyze the polarization properties of light upon propagation through metamaterial slabs in a comprehensive manner. Based on symmetry considerations, we show that all periodic metamaterials may be divided into five different classes only. It is shown that each class differently affects the polarization of the transmitted light and sustains different eigenmodes. We show how to deduce these five classes from symmetry considerations and provide a simple algorithm that can be applied to decide by measuring transmitted intensities to which class a given metamaterial is belonging to only.

We study the near-field optical behavior of Fabry-Pérot resonances in thin metal nanowires, also referred to as quasi one-dimensional plasmonic nanoantennas. From eigenmodes well beyond quadrupolar order we extract both, propagation constant and reflection phase of the guided surface plasmon polariton with superb accuracy. The combined symmetry breaking effects of oblique illumination and retardation allow the excitation of dipole forbidden, even order resonances. All measurements are supported by rigorous simulations of the experimental situation.