Vladimir Bordo

Purcell factor for a cylindrical nanocavity: ab initio analytical approach

The rigorous analytical approach for the calculation of the spontaneous decay rate for a quantum emitter located in a cylindrical cavity of arbitrary diameter and length is developed. The approach is based on the dyadic Green’s function of the Helmholtz equation, which is obtained by introducing the fictitious surface current sheets at both ends of the nanocavity. The cases when an emitter is located on the cavity axis and when the cavity length exceeds essentially its diameter are considered in further detail. The general theory is illustrated by the calculations for the system, which models a quantum dot embedded in a GaAs nanowire.

Organic nanoaggregates: a window to submicron optics

Nanoscaled photonic devices rely on a thorough understanding of the influence of microscopic morphological changes on the optoelectronic properties. Here, we investigate as a model system, organic nanofibers and microrings from para-phenylene molecules, which provide high flexibility in terms of controlled growth manipulation, while, on the other hand, showing self-assembled multiplication of individual entities. Examples on selective spectroscopy, scanning fluorescence optical microscopy, and waveguiding of individual nanofibers, as well as arrays of nanofibers are given. Both the linear optical properties, as well as the waveguiding efficiency are strongly related to the morphology of the nanoaggregates. Organic nanoaggregates, thus, are an interesting benchmark system for the investigation of the applicability of a variety of optical methods in the nanodomain.

Self-excitation of surface plasmon polaritons

The novel effect of self-excitation of surface plasmons (SESP) in a plasmonic nanocavity is predicted and its theory is developed from first principles. It is assumed that the cavity is formed by a nanogap between two metals and contains polarizable inclusions. Basing on the dyadic Greens function of the structure, the equations for the field in the cavity are investigated. It is shown that under certain conditions the field becomes unstable that leads to its self-excitation. The threshold criterion for self-excitation as well as the frequency of self-oscillation are derived in an analytical form. The SESP effect is explained in terms of a positive feedback for the polarization of inclusions provided by the field reflected from the cavity walls. Such a mechanism does not imply stimulated emission that distinguishes it from SPASER or plasmon laser.

Proposal for a self-excited electrically driven surface plasmon polariton generator

We propose a generator of surface plasmon polaritons (SPPs) which, unlike spasers or plasmon lasers, does not require stimulated emission in the system. Its principle of operation is based on a positive feedback which an ensemble of classical oscillating dipoles experiences from a reflective surface located in its near field. The generator design includes a nanocavity between two metal surfaces which contains metal nanoparticles in its interior. The whole structure is placed onto a prism surface that allows one to detect the generated SPPs in the Kretschmann configuration. The generation process is driven by a moderate DC voltage applied between the metal covers of the cavity. Both the generation criterion and the steady-state operation of the generator are investigated.We propose a generator of surface plasmon polaritons (SPPs) which, unlike spasers or plasmon lasers, does not require stimulated emission in the system. Its principle of operation is based on a positive feedback which an ensemble of classical oscillating dipoles experiences from a reflective surface located in its near field. The generator design includes a nanocavity between two metal surfaces which contains metal nanoparticles in its interior. The whole structure is placed onto a prism surface that allows one to detect the generated SPPs in the Kretschmann configuration. The generation process is driven by a moderate DC voltage applied between the metal covers of the cavity. Both the generation criterion and the steady-state operation of the generator are investigated.

Leakage radiation spectroscopy of organic/dielectric/metal systems: influence of SiO2 on exciton-surface plasmon polariton interaction

Leakage radiation spectroscopy of organic para-Hexaphenylene (p-6P) molecules has been performed in the spectral range 420-675 nm which overlaps with the p-6P photoluminescence band. The p-6P was deposited on 40 nm silver (Ag) films on BK7 glass, covered with SiO2 layers. The SiO2 layer thickness was varied in the range 5-30 nm. Domains of mutually parallelly oriented organic nanofibers were initially grown under high-vacuum conditions by molecular beam epitaxy onto a cleaved muscovite mica substrate and afterwards transferred onto the sample by a soft transfer technique. The sample placed on a flat side of a hemisphere fused silica prism with an index matching liquid was illuminated under normal incidence by a He-Cd 325 nm laser. Two orthogonal linear polarizations were used both parallel and perpendicular to the detection plane. Spectrally resolved leakage radiation was observed on the opposite side of the Ag film (i.e. at the hemisphere prism) as a function of the scattering angle. Each spectrum contains a distinct peak at a wavelength dependent angle above the critical angle. This way the dispersion curve was measured, originating from a hybrid mode, i.e. the interaction between the p-6P excitons and surface plasmon polaritons (SPPs) of the metal/dielectric boundary. The presence of the SiO2 layer considerably changes the dispersion curve in comparison to the one of the Ag/p-6P/air system. However, the Ag/SiO2/p-6P/air stack forms a stable structure allowing construction of organic plasmonic devices such as nano-lasers.

Organic nanofibers: a new window to optics of ultrasmall aggregates

Nanoscaled photonic devices rely on a thorough understanding of the influence of microscopic morphological changes on the optoelectronic properties. Here, we investigate as a model system organic nanofibers from para-phenylene molecules, which provide high flexibility in terms of controlled growth manipulation, while on the other hand showing self assembled multiplication of individual entities. Examples on selective spectroscopy, scanning fluorescence optical microscopy and waveguiding of individual nanofibers as well as arrays of nanofibers are given. Both the linear optical properties as well as the waveguiding efficiency are strongly related to the nanofibers morphology, which turn out to be an interesting benchmark system for the investigation of the applicability of a variety of optical methods in the nanodomain.

Self-excitation of Rydberg atoms at a metal surface

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Propagation properties of silver nanowires embedded in a substrate with gain

The transmittance, reflectance and absorption of silver nanowires metamaterial embedded into a semiconductor matrix with optical gain are numerically investigated. Metamaterials may suffer from appreciable dissipative losses which are inherent for all plasmonic structures. The losses can significantly be reduced by introducing optical gain in the dielectric matrix by placing atomic or molecular impurities which are pumped by an external light source to create a population inversion. We numerically analyzed the optical properties when the semiconductor host material represents a gain medium. We calculate the transmittance, reflectance and absorption at normal incidence in the visible and near infrared ranges. We observed a peculiar behavior of their optical coefficients that can be explained by observing the field redistribution on the metamaterial.

Surface plasmon amplification without inversion in plasmonic nanogaps

The theory of surface plasmon polariton (SPP) amplification in the metal-insulator-metal structure is developed from first principles. Basing on the dyadic Green’s function of the structure, an exact analytical expression for the gain coefficient is derived. It is shown that the amplification can occur without a population inversion and can reach giant (∼ 106 cm−1) values. The physical origin of this effect is associated with a positive feedback provided by the reflecting waveguide walls that does not require an external pumping. It is also predicted that the same physical phenomenon can lead to SPP generation and the corresponding threshold condition is obtained. It is stressed that such an effect does not imply stimulated emission in the structure and is principally different from SPASER.

Purcell effect for finite-length metal-coated and metal nanowires

We investigate the modification (enhancement and suppression) of the spontaneous emission rate of a dipole emitter in two configurations: inside a finite-length semiconductor nanowire surrounded by bulk metal and in the vicinity of a finite metal nanowire. Our analysis is based on a first-principle approach, which is reduced to a seminumeric one in the limit of large nanowire aspect ratios. The numerical calculations are carried out for an emitter in a GaAs nanowire embedded in Ag or Au and for that nearby an Ag or Au nanowire in vacuum or dielectric. We consider in detail the Purcell and β factors as functions of the cylinder radius, the emitter position, and the transition frequency for both configurations. We contrast the results for finite-length nanowires with those obtained in the infinite-length approximation and find considerable differences in the Purcell factor magnitude.