V. V. Klimov

Spontaneous emission rate and level shift of an atom inside a dielectric microsphere

Abstract The transition frequency shift and the spontaneous decay rate (the radiative linewidth) variation of an atom placed in a transparent dielectric microsphere are presented. It is demonstrated that with the refractive index of the microsphere material (e.g. diamond) being high enough, the size of the microsphere can be selected such that the spontaneous decay rate decreases (or increases) several times, depending on the position of the atom. At the same time, the atomic transition frequency shift proves to depend more strongly on the position of the atom, reaching high values near the surface of the microsphere.

RADIATIVE DECAY ENGINEERING BY TRIAXIAL NANOELLIPSOIDS

Radiative decay rate of an atom placed near a triaxial nanoellipsoid is investigated. Analytical results are obtained for a general case. It is shown that a triaxial ellipsoid can be used for an efficient control of the decay rate of an atom, molecule or quantum dot and for high-efficiency coupling of the far field radiation to the near-field domain. For example, the decay rate near a silver ellipsoid can be enhanced by five orders of magnitude. It is also shown, that a triaxial nanoellipsoid can be used for simultaneous efficient control of absorption and emission rates of fluorophores.

A model of an apertureless scanning microscope with a prolate nanospheroid as a tip and an excited molecule as an object

The nanotip of a needle used in apertureless optical scanning microscopy is modeled by a prolate nanospheroid, possessing resonance properties due to the plasmons excited therein. The influence of the resonant nanospheroid on a dipole decay rate of an excited molecule is considered. The relationship between the scanning signal and the molecule position and its dipole momentum orientation is found. The results predict the about one nanometer spatial resolution of some versions of SNOM.

Optical properties of a plasmonic nano-antenna: an analytical approach

The optical properties of a plasmonic nano-antenna made of two metallic nanospheroids (prolate or oblate) were investigated analytically in quasi-static approximation. It is shown that in clusters of two nanospheroids, three types of plasmonic modes can be present. Two of them can be effectively excited by a plane electromagnetic wave, while the third one can be effectively excited only by a nanolocalized light source (an atom, a molecule or a quantum dot) placed in the gap between the nanoparticles. Analytical expressions for the absorption cross-section, the enhancement of local fields and the radiative decay rate of an excited atom placed near such a nano-antenna are presented and analyzed.

Coherent perfect nanoabsorbers based on negative refraction

Based on both analytical dipole model analyses and numerical simulations, we propose a concept of coherent perfect nanoabsorbers (CPNAs) for divergent beams. This concept makes use of the properties of a slab with negative refraction and small losses. The proposed CPNA device would allow focusing radiation in nanoscale regions, and hence could be applied in optical nanodevices for such diverse purposes as reading the results of quantum computation which is based on single photon qubits.

Engineering of radiation of optically active molecules with chiral nano-meta-particles

The radiation of an optically active (chiral) molecule placed near a chiral nanosphere is investigated. The optimal conditions for engineering of radiation of optically active (chiral) molecules with the help of chiral nanoparticles are derived. It is shown that for this purpose, the substance of the chiral particle must have both e and μ negative (double negative material (DNG)) or negative μ and positive e (μ negative material (MNG)). Our results pave the way to an effective engineering of radiation of left and right molecules and to creating pure optical devices for separation of drugs enantiomers.

The influence of chiral spherical particles on the radiation of optically active molecules

Within the framework of nonrelativistic quantum electrodynamics, a theory of spontaneous emission of a chiral molecule located near a chiral (bi-isotropic) spherical particle is developed. It is shown that the structure of photons in the presence of chiral spherical particles differs significantly from the structure of usual transverse electric and transverse magnetic photons. Exact analytical expressions for a spontaneous emission decay rate of a chiral molecule with arbitrary electric and magnetic dipole moments of transition located near a chiral spherical particle with arbitrary parameters, are obtained and analyzed in detail. Simple asymptotes for the case of a nanoparticle are obtained. Substantial influence of even small chirality on a sphere made from dielectric or double negative metamaterial is found. It is shown that by using chiral spherical particles it is possible to effectively control the radiation of a given enantiomer of optically active molecules.

Detecting photons in the dark region of Laguerre-Gauss beams.

We show that a photon detector, sensitive to the magnetic field or to the gradient of electric field, can help to characterize the quantum properties of spatially-dependent optical fields. We discuss the excitation of an atom through magnetic dipole or electric quadrupole transitions with the photons of a Bessel beam or a Laguerre-Gauss (LG) beams. These spiral beams are shown to be not true hollow beams, due to the presence of magnetic fields and gradients of electric fields on beam axis. This approach paves the way to an analysis at the quantum level of the propagating light beams having a complicated spatial structure.

Comparative focusing of Maxwell and Dirac fields by negative-refraction half-space

We derive exact analytical solutions for the focusing of Maxwell photons and massless Dirac particles by half-space with negative refraction. These novel paradoxical solutions show that half-space with negative refraction cannot be simply considered as a superlens. Instead of a 2D focus spot it results in the creation of a sink of complicated spatial structure. Our analytical solutions also show substantial differences in the focusing of Maxwell and Dirac field within this geometry. We find a new manifestation of the Klein paradox which is the creation of sinks in the negative-refraction area. Possible applications and generalizations of our approach are discussed.

Plasmon oscillations in ellipsoid nanoparticles: Beyond dipole approximation

The plasmon oscillations of a metallic triaxial ellipsoid nanoparticle have been studied within the framework of the quasistatic approximation. A general method has been proposed for finding the analytical expressions describing the potential and frequencies of the plasmon oscillations of an arbitrary multipolarity order. The analytical expressions have been derived for an electric potential and plasmon oscillation frequencies of the first 24 modes. Other higher orders plasmon modes are investigated numerically.