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.
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.
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.
Leakage radiation spectroscopy of organic nanofibers composed of self-assembled organic molecules (para-Hexaphenylene,
p-6P) deposited on a thin (40-60 nm) Ag film has been performed in the spectral range 420-675
nm which overlaps with the nanofiber photoluminescence band. Using a soft transfer technqiue, domains of
mutually parallel oriented organic nanofibers were initially grown under high-vacuum conditions by molecularbeam
epitaxy onto a cleaved muscovite mica substrate and afterwards transferred onto a silver film prepared on
the glass carrier. The sample placed on a flat side of a hemisphere prism with an index matching liquid was
illuminated by either a He-Cd 325 nm laser or by white light from a bulb. In the case of laser excitation two
orthogonal linear polarizations and two different configurations of p-6P nanofibers were applied, both parallel and
perpendicular to the plane of detection. The leakage radiation was observed on the opposite side of the Ag film
at the phase matching angle. The spectrally resolved intensity of the scattered radiation has been measured as a
function of scattering angle at normally incident light. The spectrum contains a distinct peak at an wavelength
dependent angle above the critical angle. By analyzing this dispersion curve one can argue that it originates
from the interaction between the nanofiber excitons and surface plasmon polaritons of the metal film.
The rigorous analytical approach for the calculation of the spontaneous decay rate for an 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 Hertz vector potentials which describe the electromagnetic field in the system are
found as Fourier integrals over the path in the complex plane of the propagation constant. The integral equation
which determines the field Fourier transforms is derived. The Green's function is then used to calculate the field
susceptibility and the spontaneous decay rate of an emitter located inside a nanocavity. The general theory is
illustrated by the calculations for the system which models an InAs quantum dot embedded in a GaAs nanowire.
We report waveguide amplification of spontaneous emission and coherent random laser action in individual self-assembled organic nanofibers grown by high-vacuum deposition. The interpretation of the experimental results is given on the basis of simple models, including transfer matrix calculations in one-dimensionally disordered structures. We present also the numerical results for light scattering from a nanofiber which can be used as a basis for further experiments.
KEYWORDS: Nanofibers, Luminescence, Spectroscopy, Near field optics, Atomic force microscopy, Fluorescence spectroscopy, Near field scanning optical microscopy, Scanning tunneling microscopy, Molecules, Mica
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.
Non-intrusive laser-spectroscopical methods for the diagnostics of the gas-surface interaction in the near-field of a dielectric surface have been developed both experimentally and theoretically. The techniques base on either two-photon evanescent wave excitation or combined evanescent-volume wave excitation. Spectra obtained for sodium atoms at a glass-vacuum interface are quantitatively reproduced by a rigorous theoretical approach. In the case of pure evanescent wave excitation the excitation conditions can be chosen such that either the velocity distribution of desorbing atoms is determined or that atom-surface interaction parameters (polarizability of the adsorbed atoms, desorption rate, sticking coefficient) are obtained from the Autler- Townes splitting of the two-photon lines. By the use of combined evanescent-volume wave excitation one is able to distinguish optically between different groups of atoms interacting with the surface and one can extract their two- dimensional velocity distributions. In addition, information is obtained about superelastic scattering of the atoms interacting with the dielectric substrate.
In this work we study metal surface-induced changes of lifetime and transition frequency of alkali atoms and clusters, deposited onto nanoscaled insulator-metal systems. The systems are made of rough metallic surfaces (characterized by atomic force microscopy), onto which ultrathin organic films as spacer layers (characterized by LEED) are epitaxially grown. We observe an unusually small red shift of the transition frequency of Na atoms of a few hundred Megahertz, which is due to the interaction with the metal surface. This is explained by the nonlocal response of the surface, i.e., the excitation of multipole surface plasmons (MSPs) in the selvedge region of the metal surface, which is influenced by surface roughness. The MSPs should become observable also via linear optical methods such as attenuated total reflection spectroscopy. As a first step in this direction, we present linear extinction spectra of alkali cluster films that are grown on top of organic spectra layers of different length. Due to the interaction with the gold films a red shift of the dipole plasmon resonance is observed, which increases with decreasing chain length.
We theoretically analyze infrared-visible sum-frequency generation (SFG) from gas molecules near a solid. The incident IR radiation is supposed to be in resonance with one of the normal intramolecular vibrations. We separate the evolution of the molecule's internal and external degrees of freedom using an adiabatic approximation. We solve the equation of translational motion containing the `integral of collisions' with phonons in the basis of ingoing and outgoing waves. The SFG spectrum is shown to be consisting of two lines, one at the sum frequency and a satellite arising from the desorbing molecules. The line shapes obtained are determined by the rate of `collisions with phonons' as well as molecule-surface distance dependence of the vibrational frequency and linewidth.
We present the results of a theoretical investigation of the fluorescence spectrum from the gas of two-level atoms strongly driven by an evanescent wave (EW). The mean time-of-flight of atoms across the EW is supposed to be less than the relaxation times in the gas volume. Assuming the atomic absorption line to be Doppler-broadened we analyze two specific cases: (1) the atoms over the whole Doppler contour are excited by the EW in the adiabatic-following regime and (2) the EW 'burns out the hole' inside the absorption line. In case (1) in addition to the well- known Mollow triplet the line at the atomic transition frequency appears due to the transient behavior of the atoms departing the surface. In case (2) the spectrum has a sub-Doppler structure sensitive to the type of the atom-surface scattering (diffuse, specular or inelastic). In both cases the spectrum depends on the sticking probability and phases of the scattering in the ground and excited states.
An experimental investigation has been performed of sulphur hexafluoride molecules separation by diffusion through a metallized fine-porous membrane in the field of surface electromagnetic wave (SEW) induced by CO2 laser radiation. Dependencies of SF6 mixture separation coefficient are obtained upon different parameters: SEW intensity, isotropic composition, and pressure of the initial mixture. The influence of an inert gas admixture upon the separation efficiency is studied. A possible mechanism of heterogeneous separation of molecules induced by SEW is suggested.
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