In this Letter, we demonstrate experimentally that a patchwork of four metal-insulator-metal patches leads to an unpolarized wideband omnidirectional infrared absorption. Our structure absorbs 70% of the incident light on a 2.5 μm bandwidth at 8.5 μm. It paves the way to the design of wideband efficient plasmonic absorbers in the infrared spectrum.

Hydrophobic microtextures on solids provide water repellency: drops hardly stick on these materials and bounce off after impacts. Here we achieved solids decorated with a texture of variable density. Impacting water drops were observed to bounce off obliquely, demonstrating a transfer of vertical momentum in the horizontal direction, after rebound. This allows us to understand why vibrated drops move on such surface: an asymmetric dewetting takes place for each cycle of the vibration, which leads to an incremental drift of the liquid towards regions of high texture density.

The electromagnetic modes of a GaAs quantum well between two AlGaAs barriers are studied. At the longitudinal optical phonon frequency, the system supports a phonon polariton mode confined in the thickness of the quantum well that we call epsilon-near-zero mode. This epsilon-near-zero mode can be resonantly excited through a grating resulting in a very large absorption localized in the single quantum well. We show that the reflectivity can be modulated by applying a voltage. This paves the way to a new class of active optoelectronic devices working in the midinfrared and far infrared at ambient temperature.

We study the optical properties of subwavelength metallic waveguides made of nanoscale apertures in a metal. We develop analytical expressions for the fundamental optical modes in apertures. The results are in excellent agreement with finite element calculations. This model provides a physical understanding of the role of non-perfect metallic walls, and of the shape and size of the apertures. They reveal the effect of the skin depth and of the surface plasmon polariton coupling on the waveguide modes. The nanoscopic origin of the increase of the cut-off wavelength due to the electromagnetic penetration depth in the metal is described. Simple expressions and universal curves for the effective index and the cut-off wavelength of the fundamental guided mode of any rectangular metallic waveguide are presented. The results provide an efficient tool for the design of nanoscale waveguides with real metal.

Complex photonic band structures (CPBS) of transmission metallic gratings with rectangular slits are shown to exhibit strong discontinuities that are not evidenced in the usual energetic band structures. These discontinuities are located on Wood's anomalies and reveal unambiguously two different types of resonances, which are identified as horizontal and vertical surface-plasmon resonances. Spectral position and width of peaks in the transmission spectrum can be directly extracted from CPBS for both kinds of resonances.Recently, metallic films with sub-wavelength apertures became the subject of increasing interest. Experiments show that 2D arrays of sub-wavelength holes in metallic films can lead to extraordinary transmission of light [1][2][3][4][5]. These properties have been attributed to the excitation of coupled surface-plasmons on the upper and lower surfaces of the grating. The ability of these structures to control light has been shown [6,7], and applications have already been proposed in order to exploit these properties in different fields, such as electromagnetic filters or photolithography.Electromagnetic calculations have been carried out by Porto et al.[8] in order to study the mechanisms that enhance the transmission of light through metallic gratings with very narrow slits. They distinguished two different mechanisms, that is the excitation of coupled surface plasmon polaritons on both surfaces of the metallic grating, and the coupling of incident plane waves with waveguide resonances located in the slits. They correspond respectively to surface-plasmon bands and flat bands in the energetic band structure. Similar resonances located in grooves have also been observed experimentally and numerically in the reflected light of metallic gratings [9][10][11].Complex photonic band structures (CPBS) were previously calculated by Kuzmiak et al. for 2D periodic systems with metallic components [12], in order to obtain the attenuation and the lifetime of each mode. CPBS allowed a splitting of the lifetime of degenerate modes at Brillouin-zone boundaries to be observed.In this Letter, we will show that, in the case of rectangular metallic gratings, complex dispersion curves demonstrate the existence of a new kind of discontinuities. Much stronger than for 2D periodic systems, they are located on Wood's anomalies. They correspond to the transition between two different types of resonances, identified as horizontal and vertical surface-plasmon resonances. The first one is a periodic structure resonance, the second one is a FabryPerot like resonance. The discontinuity can be up to four orders of magnitude. Moreover, we will see on zero-order transmission spectra that the calculated complex frequencies are in excellent accordance not only with the spectral position, but also with the width of resonances' peaks. Fig. 1 shows the structure studied in this Letter, which is similar to the one of Porto et al. [8]. In the following, the period of the grating d = 3.5 µm and the width of the slits a = 0.5 µm will be kep...

Enhanced transmission and absorption by a silver film with a periodic array of slits has been studied numerically. We find that transmission and absorption peaks coincide and can be attributed to resonances of the structure. We show that these modes can be viewed as a coupling between cavity modes and surface plasmon polaritons. A quantitative analysis shows that the coupled mode can have a cavity mode character or a surface plasmon character depending on the distance to the crossing point of their dispersion relation. Finally, we provide a simple model for the peak transmission value by introducing the concept of radiative yield.

We investigate the mechanisms involved in the funneling of the optical energy into sub-wavelength grooves etched on a metallic surface. The key phenomenon is unveiled thanks to the decomposition of the electromagnetic field into its propagative and evanescent parts. We unambiguously show that the funneling is not due to plasmonic waves flowing toward the grooves, but rather to the magnetoelectric interference of the incident wave with the evanescent field, this field being mainly due to the resonant wave escaping from the groove.Plasmonics, as the science of the efficient coupling of photons with free electron gas oscillation modes at the surface of metals, appears as an inescapable solution for the design and realization of optical nano antennas [1]. Numerous cutting edge applications are based on nanoantennas like biosensing [2], gas sensing [3], photovoltaic [4] or infrared photodetection [5] which exploit the intense local electromagnetic field in a confined volume [6][7][8]. Now, the specific matter of total photon harvesting at the nanometric scale, i.e. designing an antenna able to couple all the incident optical power with a nanoabsorber, remains challenging [1,[7][8][9]. The natural twostep antenna sequence (collection of light, then concentration) has been extensively studied in structures made of a metallic subwavelength grating surrounding a target [6,[10][11][12][13][14]. The underlying mechanism involves SPP excitation (collection) and propagation (concentration) along the grating until the coupling with the target. Such structures, though, are designed to collect light at a specific incidence angle, which is obviously a strong practical limitation.In contrast, quasi-isotropic perfect transmission is obtained through very narrow slits drilled in a metallic membrane [15,16]. This perfect transmission is successfully explained by a localized Fabry-Perot resonance in the slits [17]. However the funneling, namely the mechanism responsible for the redirection and subsequent concentration of the whole incident energy flow, from the surface toward the tiny aperture of the slits, remains unclear. Yet, a pictorial model of the underlying physics is of a key importance for the design of efficient nanoantennas.Such a model is given by the energetic point of view [19]: Poynting vector streamlines distinctly show that the incident flow bends when reaching the metal surface, and then propagates along the interface toward the slits. This fits with the intuitive explanation, inspired by the SPP excitation process, that plasmonic waves drive the funneling sequence [20]. Furthermore, quasicylindric waves were recently identified as the dominant short-range propagation process of the field amplitude along the surface of the grating [21,22]. Nevertheless, even if the evanescent waves are naturally assumed to concentrate the energy toward the apertures of the slits, no specific study of the light funneling has so far been carried out to our knowledge.In this letter, we definitely unveil the funneling process, and highl...

We demonstrate the total extinction of the reflectivity for a transverse magnetic polarized wave on a gold surface etched on 6% of its area by both narrow (150 nm) and deep (2 μm) grooves. These high aspect ratio metallic grooves were fabricated using a mold cast technique based on an electrolytic growth of gold. They exhibit two resonance peaks corresponding to the first and second cavity modes inside the grooves. We also evidence the incidence-invariance of their spectral response, which undoubtedly shows the localized nature of the resonances. These experimental results confirm the prediction of total funneling of light in very narrow grooves.