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emitting light at a wavelength . Although this model
neglects the intrinsic losses and finite bandwidth of real
molecules and quantum dots, it is often used in the litera-
FIG. 1 (color online). (a) Schematic of the periodic system composed of nanoring antennas fed by an array of coherent emitters (represented as double arrows). Inset: Geometry of the Au rings. (b) Normalized power radiated upwards (or downwards) by a square lattice of dipoles through the unit-cell area a2 ¼ 1 m  1 m. Black and red solid curves: solutions of Eqs. (6) and (7) for horizontal and vertical dipoles, respectively. Black and red circles: numerical simulations with commercial finite element code.
In this Letter we try to provide a first answer to this question by studying a model system where a generic array of coherent dipoles interacts with a periodic arrangement of metallic nanorings [Fig. 1(a)]. The emission can be enhanced by two families of resonances—the first associated with diffractive Rayleigh anomalies induced by the in-phase emitters, the other being the localized surface plasmons (SPs) sustained by the metallic nanorings. By adjusting the dimensions of the rings and/or the periodicity, we show that it is possible to hybridize the Rayleigh anomalies and certain SP modes, leading to anticrossings characterized by strong variations in the linewidth and shape of the emission peaks.
0031-9007= 12=108(14)=147401(5)
147401-1
Ó 2012 American Physical Society
PRL 108, 147401 (2012)
PHYSICAL REVIEW LETTERS
week ending 6 APRIL 2012
The emitters are treated as lossless classical dipoles
PRL 108, 147401 (2012)
PHYSICAL REVIEW LETTERS
week ending 6 APRILical Emitters Coupled to an Array of Nanosize Metallic Antennas
T. V. Teperik1 and A. Degiron1,2,* 1Univ. Paris-Sud, Institut d’Electronique Fondamentale, UMR 8622, Orsay F-91405, France
Thus, the use of optical antennas and collective coherent effects appear today as two very distinct yet
complementary strategies to control the spontaneous emission of subwavelength sources. One can therefore wonder if any benefit would arise from combining these two approaches, i.e., by considering an ensemble of in-phase oscillators coupled to optical antennas.
DOI: 10.1103/PhysRevLett.108.147401
PACS numbers: 78.66.Bz, 73.20.Mf, 78.55.Àm, 78.67.Àn
Optical nanoantennas have recently emerged as powerful tools to tailor the spontaneous emission of molecules and quantum dots [1]. Most antenna designs are based on metallic nanoparticles that sustain localized surface plasmon (SP) resonances [2–10]. The high local fields associated with localized SPs are either employed to maximize the absorption cross section or the radiative decay rate of the emitter through the Purcell effect [11]. Both approaches make it possible to enhance the rate of spontaneous emission by a substantial amount which can exceed 1000-fold in certain experimental works [8]. The resonant environment provided by a metallic nanoantenna can also be used to shape the angular distribution of the emitted light, as was shown for instance with multielement antennas [2,12], bimetallic dimmers [13] and individual metallic particles [9,14]. More generally, these spectacular results represent the latest developments to leverage the properties of dipolar emitters through judicious design of their environment [15–19].
Interestingly, none of these efforts fundamentally alter the fact that spontaneous emission is a random process leading to the emission of incoherent light. To generate coherent light, it is necessary to use an alternative approach based on enabling superradiance in an ensemble of emitters. Superradiance corresponds to the situation where individual sources come to interact through the radiation field, inducing coherent correlations within the system [20]. In this configuration, the emitters are oscillating in phase, generating a signal proportional to the square of their number in the directions of space where they interfere constructively. First theorized by Dicke for a system of two-level atoms [21], superradiance has been evidenced in many systems [22–24], including luminescent quantum dots that are also studied in the context of optical nanoantennas [25].
2CNRS Orsay, F-91405, France (Received 7 November 2011; published 3 April 2012)
We study the properties of an array of Au ring nanoantennas fed by an ensemble of coherent emitters. The luminescence of the emitters is strongly enhanced at certain wavelengths due to the excitation of two types of resonances—the diffractive Rayleigh anomalies associated with the opening of new diffraction orders and the localized surface plasmons of the nanoantennas. We show that the two families of resonances can spectrally overlap and lead to anticrossings or cumulative enhancements depending on the symmetries of the modes. This rich optical behavior induces marked changes in the linewidth, shape, and amplitude of the peaks and could be potentially used to tune the luminescence of superradiant sources with new flexibility.