Search

The constant miniaturization trend in nanophotonics challenges some of the theoretical tools at our disposal: Analytical shortcuts such as the dipolar and paraxial approximation become unapplicable, and the computational cost of fully numerical studies often renders them impractical. A basic electromagnetic property, the optical helicity, and the use of more abstract tools inspired by it, are rising to meet the challenge.

Predicting the optical response of macroscopic arrangements of individual scatterers is a computational challenge because the problem involves length scales across multiple orders of magnitude. We present a full-wave optical method to efficiently compute the scattering of light at objects that are arranged in biperiodic arrays. Multiple arrays or homogeneous thin films can be stacked to build up an entire multicomposite material in the third dimension. The scattering properties of the individual objects in each array are described by the T-matrix formalism. Therefore, arbitrarily shaped objects and even molecules can be the basic constituent of the arrays. Taking the T-matrix of the individual scatterer as the point of departure we can explain the optical properties of the bulk material from the scattering properties of its constituents. We use solutions of Maxwell’s equations with well-defined helicity. Therefore, chiral media are particularly easy to consider as materials for both scatterers and embedding media. We exemplify the efficiency of the algorithm with an exhaustive parametric study of anti-reflective coatings for solar cells made from cylinders with a high degree of helicity preservation. The example shows a speed-up factor of about 500 with respect to finite-element computations. A second example specifically exploits the use of helicity modes to investigate the enhancement of the circular dichroism signal in a chiral material.

Les informations fournies dans le résumé des caractéristiques du produit des médicaments sous autorisation temporaire d’utilisation (ATU) sont souvent succinctes et en langue étrangère, complexifiant la compréhension pour le patient. L’objectif de cette étude est d’évaluer l’observance des patients disposant d’un traitement chronique sous ATU dispensé aux rétrocessions.

Metasurfaces made from densely packed resonant wavelength-scale particles enable abrupt modulation of impinging electromagnetic radiation within an ultrathin surface. Combining duality symmetry of particles and rotational symmetry of their arrangement led to the development of Huygens’ metasurfaces with perfect transmission. However, so far, when identical particles are considered, only their dipolar multipolar contributions are engineered. There, the achievable phase coverage at a fixed wavelength when modifying the period is smaller than 2π, being a clear limitation for applications. To lift such limitation, we consider dipolar-quadrupolar Huygens’ metasurfaces. They consist of scatterers that require a dipolar and a quadrupolar term to capture their response. We show that such metasurfaces offer access to the desired 2πphase coverage while preserving the perfect efficiency when the conditions of duality and symmetry continue to be met. We also propose core-multishell and disk-multiring particles made from realistic materials to meet the requirements and that can be used to build such metasurfaces. Our results are important as a theoretical basis for large-scale fabrications in imaging and integrated optics.

Mie-resonant high-index dielectric nanoparticles and metasurfaces have been suggested as a viable platform for enhancing both electric and magnetic dipole transitions of fluorescent emitters. While the enhancement of the electric dipole transitions by such dielectric nanoparticles has been demonstrated experimentally, the case of magnetic-dipole transitions remains largely unexplored. Here, we study the enhancement of spontaneous emission of Eu3+ions, featuring both electric and magnetic-dominated dipole transitions, by dielectric metasurfaces composed of Mie-resonant silicon nanocylinders. By coating the metasurfaces with a layer of an Eu3+doped polymer, we observe an enhancement of the Eu3+emission associated with the electric (at 610 nm) and magnetic-dominated (at 590 nm) dipole transitions. The enhancement factor depends systematically on the spectral proximity of the atomic transitions to the Mie resonances as well as their multipolar order, both controlled by the nanocylinder size. Importantly, the branching ratio of emission via the electric or magnetic transition channel can be modified by carefully designing the metasurface, where the magnetic dipole transition is enhanced more than the electric transition for cylinders with radii of about 130 nm. We confirm our observations by numerical simulations based on the reciprocity principle. Our results open new opportunities for bright nanoscale light sources based on magnetic transitions.

We present an electromagnetic chirality measure for 2D arrays of subwavelength periodicities under normal illumination. The calculation of the measure uses only the complex reflection and transmission coefficients from the array. The measure allows the ordering of arrays according to their electromagnetic chirality, which further allows a quantitative comparison of different design strategies. The measure is upper bounded, and the extreme properties of objects with high values of electromagnetic chirality make them useful in both near- and far-field applications. We analyze the consequences that different possible symmetries of the array have on its electromagnetic chirality. We use the measure to study four different arrays. The results indicate the suitability of helices for building arrays of high electromagnetic chirality, and the low effectiveness of a substrate for breaking the transverse mirror symmetry.

We present a study of the properties of the transversal “spin angular momentum” and “orbital angular momentum” operators. We show that the “spin angular momentum” operators are generators of spatial translations that depend on helicity and frequency and that the “orbital angular momentum” operators generate transformations that are a sequence of this kind of translation and rotation. We give some examples of the use of these operators in light–matter interaction problems. Their relationship with the helicity operator allows us to involve electromagnetic duality symmetry in the analysis. We also find that simultaneous eigenstates of the three “spin” operators and parity define a type of standing mode that has recently been singled out for the interaction of light with chiral molecules. With respect to the relationship between “spin angular momentum,” polarization, and total angular momentum, we show that, except for the case of a single plane wave, the total angular momentum of the field is decoupled from its vectorial degrees of freedom even in the regime in which the paraxial approximation holds. Finally, we point out a relationship between the three “spin” operators and the spatial part of the Pauli–Lubanski four vector.

We unveil the relationship between two anomalous scattering processes known as Kerker conditions and the duality symmetry of Maxwell equations. We generalize these conditions and show that they can be applied to any particle with cylindrical symmetry, not only to spherical particles as the original Kerker conditions were derived for. We also explain the role of the optical helicity in these scattering processes. Our results find applications in the field of metamaterials, where new materials with directional scattering are being explored.

Abstract: A leukemic child developed a pulmonary leukemic infiltration, confirmed by open lung biopsy. His radiograph showed a mixed interstitial and nodular pattern. Nodular lung lesions are rare in pediatric patients and may exceptionally represent leukemic invasion.