Theory of fishnet negative-index optical metamaterials

We theoretically study fishnet metamaterials at optical frequencies. In contrast to earlier works, we provide a microscopic description by tracking the transversal and longitudinal flows of energy through the fishnet mesh composed of intersecting subwavelength plasmonic waveguides. The analysis is supported by a semi-analytical model based on surface-plasmon coupled-mode equations, which provides accurate formulas for the fishnet refractive index, including the real-negative and imaginary parts. The model simply explains how the surface plasmons couple at the waveguide intersections and it shines new light on the fishnet negative-index paradigm at optical frequencies. Extension of the theory for loss-compensated metamaterials with gain media is also presented.Comment: 4 figure

Homogenization of an ensemble of interacting resonant scatterers

We study theoretically the concept of homogenization in optics using an ensemble of randomly distributed resonant stationary atoms with density $\rho$. The ensemble is dense enough for the usual condition for homogenization, viz. $\rho\lambda^3 \gg 1$, to be reached. Introducing the coherent and incoherent scattered powers, we define two criteria to define the homogenization regime. We find that when the excitation field is tuned in a broad frequency range around the resonance, none of the criteria for homogenization is fulfilled, meaning that the condition $\rho\lambda^3\gg 1$ is not sufficient to characterize the homogenized regime around the atomic resonance. We interpret these results as a consequence of the light-induced dipole-dipole interactions between the atoms, which implies a description of scattering in terms of collective modes rather than as a sequence of individual scattering events. Finally, we show that, although homogenization can never be reached for a dense ensemble of randomly positioned laser-cooled atoms around resonance, it becomes possible if one introduces spatial correlations in the positions of the atoms or non-radiative losses, such as would be the case for organic molecules or quantum dots coupled to a phonon bath.Comment: 9 pages, 5 figures. Corrected mistakes in reference

Slow-wave effect and mode-profile matching in Photonic Crystal microcavities

Physical mechanisms involved in the light confinement in photonic crystal slab microcavities are investigated. We first present a full three-dimensional numerical study of these microcavities. Then, to gain physical insight into the confinement mechanisms, we develop a Fabry-Perot model. This model provides accurate predictions and sheds new light on the physics of light confinement. We clearly identify two mechanisms to enhance the Q factor of these microcavities. The first one consists in improving the mode-profile matching at the cavity terminations and the second one in using a slow wave in the cavity.Comment: accepted for publication in Phys. Rev. B, 8 pages, 4 figure

Single-Proton Removal Reaction Study of 16B

The low-lying level structure of the unbound system $^{16}$B has been investigated via single-proton removal from a 35 MeV/nucleon $^{17}$C beam. The coincident detection of the beam velocity $^{15}$B fragment and neutron allowed the relative energy of the in-flight decay of $^{16}$B to be reconstructed. The resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is argued that this feature corresponds to a very narrow ($\Gamma \ll$100 keV) resonance, or an unresolved multiplet, with a dominant $\pi (p_{3/2})^{-1} \otimes \nu (d_{5/2}^3)_{J=3/2^+}$ + $\pi (p_{3/2})^{-1} \otimes \nu (d_{5/2}^2,s_{1/2})_{J=3/2^+}$ configuration which decays by d-wave neutron emission.Comment: 16 pages, 5 figures, 1 table, submitted to Phys. Lett.

Difference between penetration and damping lengths in photonic crystal mirrors

Different mirror geometries in two-dimensional photonic crystal slabs are studied with fully-vectorial calculations. We compare their optical properties and, in particular, we show that, for heterostructure mirrors, the penetration length associated with the delay induced by distributed reflection is not correlated to the characteristic damping length of the electromagnetic energy distribution in the mirror. This unexpected result evidences that the usual trade-off between short damping lengths and large penetration lengths that is classically encountered in distributed Bragg reflectors can be overcome with carefully designed photonic crystal structures.Comment: to be published in Applied Physics Letters, 4 pages, 4 figure

First-principles method for high-QQ photonic crystal cavity mode calculations

We present a first-principles method to compute radiation properties of ultra-high quality factor photonic crystal cavities. Our Frequency-domain Approach for Radiation (FAR) can compute the far-field radiation pattern and quality factor of cavity modes $\sim 100$ times more rapidly than conventional finite-difference time domain calculations. It also provides a simple rule for engineering the cavity's far-field radiation pattern

Semi-analytic method for slow light photonic crystal waveguide design

We present a semi-analytic method to calculate the dispersion curves and the group velocity of photonic crystal waveguide modes in two-dimensional geometries. We model the waveguide as a homogenous strip, surrounded by photonic crystal acting as diffracting mirrors. Following conventional guided-wave optics, the properties of the photonic crystal waveguide may be calculated from the phase upon propagation over the strip and the phase upon reflection. The cases of interest require a theory including the specular order and one other diffracted reflected order. The computational advantages let us scan a large parameter space, allowing us to find novel types of solutions.Comment: Accepted by Photonics and Nanostructures - Fundamentals and Application