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The recent advent of digital coding metasurfaces notably simplifies the design of functional devices, enabling one to manipulate electromagnetic waves in exotic ways using specifically arranged coding elements representing discrete phase states. Here, we propose a design of dielectric coding metasurface with diverse functionalities, which are achieved by encoding the metasurface unit cells with different coding sequences. As proofs of concept, we demonstrate the possibility of realizing five distinct functionalities for the normal incidence of plane microwaves: anomalous reflection, multibeam generation, diffuse scattering, beam focusing, and vortex beam generation. The near-field distributions and far-field scattering patterns are obtained by full-wave numerical simulations to analyze the behavior of the waves in each of the cases and illustrate our general theoretical predictions. [ABSTRACT FROM AUTHOR]

We develop a general theory of optical activity of semiconductor nanocrystals whose chirality is induced by a small perturbation of their otherwise achiral electronic subsystems. The optical activity is described using the quantum-mechanical expressions for the rotatory strengths and dissymmetry factors introduced by Rosenfeld. We show that the rotatory strengths of optically active transitions are decomposed on electric dipole and magnetic dipole contributions, which correspond to the electric dipole and magnetic dipole transitions between the unperturbed quantum states. Remarkably, while the two kinds of rotatory strengths are of the same order of magnitude, the corresponding dissymmetry factors can differ by a factor of 105. By maximizing the dissymmetry of magnetic dipole absorption one can significantly enhance the enantioselectivity in the interaction of semiconductor nanocrystals with circularly polarized light. This feature may advance chiral and analytical methods, which will benefit biophysics, chemistry, and pharmaceutical science. The developed theory is illustrated by an example of intraband transitions inside a semiconductor nanocuboid, whose rotatory strengths and dissymmetry factors are calculated analytically. [ABSTRACT FROM AUTHOR]

The coherent coupling of quantum dots is a sensitive indicator of the energy and phase relaxation processes taking place in the nanostructure components. We formulate a theory of low-temperature, stationary photoluminescence from a quantum-dot molecule composed of two spherical quantum dots whose electronic subsystems are resonantly coupled via the Coulomb interaction. We show that the coupling leads to the hybridization of the first excited states of the quantum dots, manifesting itself as a pair of photoluminescence peaks with intensities and spectral positions strongly dependent on the geometric, material, and relaxation parameters of the quantum-dot molecule. These parameters are explicitly contained in the analytical expression for the photoluminescence differential cross section derived in the paper. The developed theory and expression obtained are essential in interpreting and analyzing spectroscopic data on the secondary emission of coherently coupled quantum systems. [ABSTRACT FROM AUTHOR]

Despite chiral metamaterials being widely appreciated for their giant optical activity and negative refractive index with respect to the transmitted electromagnetic waves, little research efforts are devoted to effects occurring upon optical reflection from such metamaterials. Here, we theoretically demonstrate highly energy-efficient cross-polarization conversion for a normally incident wave reflecting from metamaterial with a broken four-fold symmetry of chiral structure. We do this by designing metamaterial that makes the polarization plane of a linearly polarized electromagnetic wave reflected from its surface almost perpendicular to the polarization plane of the incident wave. Using reflection from this metamaterial, one can also freely convert between left-handed and right-handed circular polarizations without significant energy loss. The proposed chiral metamaterial may prove useful in electromagnetic communication systems, polarization controllable antennas, and on-chip biomedical sensors. [ABSTRACT FROM AUTHOR]