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ABSTRACT: We present a transformation-optics approach which sheds analytical insight into the impact that spatial dispersion has on the optical response of separated dimers of metallic nanowires. We show that nonlocal effects are apparent at interparticle distances one order of magnitude larger than the longitudinal plasmon decay length, which coincides with the spatial regime where electron tunneling phenomena occur. Our method also clarifies the interplay between nonlocal and radiation effects taking place in the nanostructure, yielding the dimer dimensions that optimize its light harvesting capabilities.
Physical review. B, Condensed matter 12/2012; 86(24):241110(R).
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ABSTRACT: One-dimensional light harvesting structures with a realistic geometry nano-patterned on an opaque metallic film are optimized to render high transmission efficiencies at optical and infrared frequencies. Simple design rules are developed for the particular case of a slit-groove array with a given number of grooves that are symmetrically distributed with respect to a central slit. These rules take advantage of the hybridization of Fabry-Perot modes in the slit and surface modes of the corrugated metal surface. Same design rules apply for optical and infrared frequencies. The parameter space of the groove array is also examined with a conjugate gradient optimization algorithm that used as a seed the geometries optimized following physical intuition. Both uniform and nonuniform groove arrays are considered. The largest transmission enhancement, with respect to a uniform array, is obtained for a chirped groove profile. Such relative enhancement is a function of the wavelength. It decreases from 39 % in the optical part of the spectrum to 15 % at the long wavelength infrared.
Optics Express 11/2012; 20(23):25441-53. · 3.59 Impact Factor
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ABSTRACT: We demonstrate that the interaction between two emitters can be controlled by means of the efficient excitation of surface plasmon modes in graphene. We consider graphene surface plasmons supported by either two-dimensional graphene sheets or one-dimensional graphene ribbons, showing in both cases that the coupling between the emitters can be strongly enhanced or suppressed. The super- and subradiant regimes are investigated in the reflection and transmission configurations. Importantly, the length scale of the coupling between emitters, which in vacuum is fixed by the free-space wavelength, is now determined by the wavelength of the graphene surface plasmons, which can be extremely short and can be tuned at will via a gate voltage.
Phys. Rev. B. 04/2012; 85(15).
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ABSTRACT: In this paper a theoretical study is made on the scattering of surface plasmon polaritons by a finite periodic array of one-dimensional
rectangular grooves. Our approach is based on a multimodal expansion technique. We have found that the geometrical parameters
of the array can be properly tuned to achieve optimal performance of the structure either as a Bragg reflector or as a converter
of surface plasmon polaritons into light. Most importantly, such functionalities can be fully achieved with a relatively small
number of grooves.
Applied Physics A 04/2012; 89(2):251-258. · 1.63 Impact Factor
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ABSTRACT: We develop an insightful transformation-optics approach to investigate the impact that nonlocality has on the optical properties of plasmonic nanostructures. The light-harvesting performance of a dimer of touching nanowires is studied by using the hydrodynamical Drude model, which reveals nonlocal resonances not predicted by previous local calculations. Our method clarifies the interplay between radiative and nonlocal effects in this nanoparticle configuration, which enables us to elucidate the optimum size that maximizes its absorption and field enhancement capabilities.
Physical Review Letters 03/2012; 108(10):106802. · 7.37 Impact Factor
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ABSTRACT: We theoretically investigate the amplification of extraordinary optical transmission (EOT) phenomena in periodic arrays of subwavelength apertures incorporating gain media. In particular, we consider a realistic structure consisting of an opaque silver film perforated by a periodic array of slits and clad on each side by an optically pumped dielectric thin film containing rhodamine dye molecules. By solving the semiclassical electronic rate equations coupled to rigorous finite-element simulations of the electromagnetic fields, we show how the resonant electric-field enhancement associated with EOT properties enables complete ohmic loss compensation at moderate pump intensity levels. Furthermore, our calculations show that, as a consequence of the strong spatial hole-burning effects displayed by the considered structures, three separate regimes of operation arise: the system can behave as an absorber, an optical amplifier or a laser, depending on the value of the pump intensity. A discussion on the feasibility of reaching the lasing regime in the considered class of structures is also presented.
New Journal of Physics 01/2012; 14(1):013020. · 4.18 Impact Factor
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ABSTRACT: We study the generation of entanglement between two distant qubits mediated
by the surface plasmons of a metallic waveguide. We show that a V-shaped
channel milled in a flat metallic surface is much more efficient for this
purpose than a metallic cylinder. The role of the misalignments of the dipole
moments of the qubits, an aspect of great importance for experimental
implementations, is also studied. A careful analysis of the quantum-dynamics of
the system by means of a master equation shows that two-qubit entanglement
generation is essentially due to the dissipative part of the effective
qubit-qubit coupling provided by the surface plasmons. The influence of a
coherent external pumping, needed to achieve a steady state entanglement, is
discussed. Finally, we pay attention to the question of how to get information
experimentally on the degree of entanglement achieved in the system.
12/2011;
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ABSTRACT: In this paper, we analyze how transformation optics recipes can be applied to control the flow of surface plasmons on metal–dielectric interfaces. We study in detail five different examples: a cylindrical cloak, a beam shifter, a right-angle bend, a lens and a ground-plane cloak. First, we demonstrate that only the modification of the electric permittivity and magnetic permeability in the dielectric side can lead to almost perfect functionalities for surface plasmons. We also show that, thanks to the quasi two-dimensional (2D) character of surface plasmons and their inherent polarization, applying conformal and quasiconformal mapping techniques allows one to design plasmonic devices in which only the isotropic refractive index of the dielectric film needs to be engineered.
New Journal of Physics 03/2011; 13(3):033011. · 4.18 Impact Factor
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ABSTRACT: It is shown that submicrometer holes with very acute angles present extraordinary optical transmission peaks associated to strongly localized modes. The positions of these peaks are: (i) strongly redshifted with respect to the peak position that could be expected if the considered hole were in a film made of perfect electric conductor, (ii) independent on the angle of incidence for a large range of angles and (iii) strongly dependent on the direction of the incident electric field. In addition, it is demonstrated that these properties are linked to the mechanisms leading to the existence of channel-plasmon-polaritons.
Optics Express 11/2010; 18(23):23691-7. · 3.59 Impact Factor
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ABSTRACT: In this paper we design an acoustic metamaterial for broadband sound blockage that is easy to fabricate and presents tunable capabilities. Two adjacent holey plates are predicted to support a gap mode which is responsible of a forbidden band, displaying a negative effective bulk modulus. This acoustic metamaterial exhibits a weak dispersion with parallel momentum implying that strong attenuation appears for a broad range of angles of incident sound. Its bandwidth can be tailored at will by varying the separation between the two holey plates.
Applied Physics Letters 09/2010; 97(13):134106-134106-3. · 3.84 Impact Factor
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ABSTRACT: We present an analytical expression for the electromagnetic field at the surface radiated by a hole in a metal film. This expression is valid for any metal, from the optical range to longer wavelengths, and for distances to the hole larger than a few tens of nanometers. The field pattern presents a rich behavior, showing three regions (a complex short distance, an intermediate range dominated by surface plasmon polaritons, and a long-distance one dominated by Norton waves). The crossover distances between these regimes depend strongly on both the wavelength and the angle with respect to the incident field.
Physical Review Letters 08/2010; 105(7):073902. · 7.37 Impact Factor
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physica status solidi (RRL) - Rapid Research Letters 07/2010; 4(10):250 - 252. · 2.22 Impact Factor
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ABSTRACT: In this paper a theoretical study on transmission phenomena of horizontally polarized shear waves propagating through a subwavelength solid probe surrounded by ridges is presented. In this context, the resonant components responsible for enhanced transmission and elastic beaming are identified as Fabry–Perot resonances inside the probe, and ridge induced Love waves. Apart from the fundamental interest, it is envisaged that the ability to enhance elastic vibrations through subwavelength channels and to focus the emerged field, will give rise to improved ultrasonic devices for sensing and testing applications.
Applied Physics Letters 06/2010; 96(23):233505-233505-3. · 3.84 Impact Factor
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ABSTRACT: The optical emittance of a hole pair perforated in an opaque metal film is
studied from first-principles using the coupled-mode method. The geometrical
simplicity of this system helps to understand the fundamental role played by
surface plasmon polaritons (SPPs) in its optical response. A SPP interference
model without fitting parameters is developed from the rigorous solution of
Maxwell's equations. The calculations show that the interference pattern of the
hole pair is determined by two scattering mechanisms: (i) re-illumination of
the holes by the in-plane SPP radiation and (ii) an effective impedance
depending on the single-hole response. The conditions for constructive and
destructive interference only depend on the phase difference provided by each
of the two scattering mechanisms.
05/2010;
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ABSTRACT: Enhanced optical transmission (EOT) through a single aperture is usually achieved by exciting surface plasmon polaritons with periodic grooves. Surface plasmon polaritons are only excited by p-polarized incident light, i.e. with the electric field perpendicular to the direction of the grooves. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. A 25 fold increase is measured as compared to the case without the dielectric film. Transmission measurements are compared with a coupled mode method and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.
Optics Express 04/2010; 18(9):9722-7. · 3.59 Impact Factor
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ABSTRACT: The light transmission properties of holey metal films in the metamaterial limit, where the unit length of the periodic structures is much smaller than the operating wavelength, are analyzed theoretically utilizing the modal expansion formalism. A detailed derivation of the transmission coefficients of both one-dimensional (1D) slit and 2D hole arrays is presented. We show that under certain assumptions the transmission coefficient becomes unity independent of the parallel momentum of the incident field. This result indicates that holey metal films can be used as endoscopes; i.e. they are capable of transforming an image with subwavelength resolution from the input to the output surface of the film. We also demonstrate how such films can effectively be mapped into homogenous anisotropic films with optical properties controlled by the geometrical parameters of the holes. Lastly, the subwavelength imaging properties of an endoscope based on a 1D slit array is demonstrated for p-polarized light using numerical simulations.
New Journal of Physics 12/2009; 11(12):123013. · 4.18 Impact Factor
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ABSTRACT: Enhanced polarization conversion in reflection for the Otto and Kretschmann configurations is introduced as a new method for hybrid-mode spectroscopy. Polarization conversion in reflection occurs when hybrid modes are excited in a guiding structure composed of at least one anisotropic medium. In contrast to a dark dip, in this case modes are associated with a peak in the converted reflectance spectrum, increasing the detection sensitivity and avoiding confusion with reflection dips associated with other processes, such as transmission.
Optics Letters 12/2009; 34(24):3911-3. · 3.40 Impact Factor
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ABSTRACT: Channel plasmon polaritons (CPPs) propagating along the bottom of V-grooves cut into a metal were recently shown to exhibit strong confinement combined with low propagation loss, a feature that makes this guiding configuration very promising for the realization of ultracompact photonic components. Here, we present a comprehensive study of radiation nanofocusing with CCPs propagating along subwavelength metal grooves that are terminated with various types of tapers of different lengths. Tapered V-grooves are fabricated in a gold film using a focused ion beam milling technique, with the tapering being realized by gradually decreasing the groove width and/or depth (in different way for different structures), and characterized at telecom wavelengths with a collection scanning near-field optical microscope. Efficient CPP nanofocusing is directly demonstrated featuring a field intensity enhancement of up to ~130 for optimal taper configurations. Experimental observations are found to be concurrent with three-dimensional finite-difference time-domain electromagnetic simulations, predicting the possibility of reaching an intensity enhancement of ~1200 and opening thereby exciting perspectives for practical applications of CPP nanofocusing.
New Journal of Physics 11/2009; 11(11):113043. · 4.18 Impact Factor
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ABSTRACT: We explore the transmission and beaming properties of a single subwavelength slit flanked by a finite array of indentations made on a thick metallic film for both s- and p-polarizations. If a dielectric slab is placed onto the metal film, excited dielectric waveguide modes drastically change the diffraction of a plane wave. We show that if a dielectric slab is placed at the incoming face of the film, the transmission can be greatly enhanced for wavelengths which are close to the Bragg reflection condition. For the same wavelengths, the waveguide modes can be redirected into a highly collimated beam within a few degrees; however, in this case, the slab must be placed at the outgoing face of the film.
Journal of Optics A Pure and Applied Optics 09/2009; 11(12):125702. · 1.92 Impact Factor
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ABSTRACT: We propose a metamaterial approach to route terahertz waves that features subwavelength confinement in the transverse plane. The guiding mechanism is based on geometrically induced electromagnetic modes sustained by corrugated metallic wedges, whose characteristics resemble those of wedge plasmon polaritons at telecom and optical frequencies. Additionally, frequency selective focusing and slowing down of terahertz radiation based on the proposed wedge waveguides are presented.
Optics Letters 08/2009; 34(13):2063-5. · 3.40 Impact Factor
