We have investigated bound modes in finite linear chains of dielectric particles of various lengths, interparticle spacing
and particle materials. Through a unique application of the multisphere Mie scattering formalism, we have developed
numerical methods to calculate eigen-optical modes for various arrays of particles. These numerical methods involve
the use of the multisphere scattering formalism as the entries in <i>N</i>×<i>N</i> matrices where N represents the number of particles
in the chain. Eigenmodes of these matrices correspond to the eigen-optical modes of interest. We identified the
eigenmodes with the highest quality factor by the application of a modified version of the Newton-Raphson algorithm.
We found that convergence is strong using this algorithm for linear chains of up to several hundreds of particles. By
comparing the dipolar approach with the more complex approach which utilizes a combination of both dipolar and
quadrupolar approaches, we demonstrated that the dipolar approach has an accuracy of approximately <i>99%</i>. We found
that the quality factor <i>Q</i> of the mode increases with the cubed value of the number of particles in chain in agreement
with the previously developed theory, the effects of disordering of particle sizes and inter-particle distances will be
Low-dimensional ordered arrays of dielectric particles can possess bound optical modes having an extremely high
quality factor depending on the material used. If these arrays consist of metal particles, then they cannot have a high
quality factor because their light absorption restricts performance. In this paper we address the following question: can
bound modes be formed in dielectric systems where the absorption of light is negligible? Our investigation of circular
arrays of spherical particles within the framework of the multisphere Mie scattering theory using the simplest dipolar-like
approach shows that (1) high quality modes in an array of <i>10</i> or more particles can be attained at least for a
refractive index <i>n</i><sub>r</sub> > 2, so optical materials like TiO<sub>2</sub> or GaAs can be used; (2) the most bound modes have nearly
transverse polarization perpendicular to the circular plane; (3) in a particularly interesting case of TiO<sub>2</sub> particles (rutile
phase, n<sub>r</sub> = <i>2.7</i>), the quality factor of the most bound mode increases almost by an order of magnitude with the addition
of 10 extra particles, while for particles made of GaAs the quality factor increases by almost two orders of magnitude
with the addition of ten extra particles. The consideration of higher multipole contributions has demonstrated that the
error of the dipolar approach does not exceed one percent if the refractive index <i>n</i><sub>r</sub> is greater than 2. Minimum
acceptable disordering not affecting the quality factor is studied.
We investigate the lasing modes in diffusive random media with local pumping. The reabsorption of emitter light suppresses the feedback from the unpumped part of the sample and effectively reduces the system size. The lasing modes are dramatically different from the quasimodes of the passive system (without gain or absorption). Even if all the quasimodes of a passive diffusive system are extended across the entire sample, the lasing modes are still confined in the pumped volume with an exponential tail outside it. The reduction of effective system volume by absoption broadens the distribution of decay rates of quasimodes and facilitates the occurrence of discrete lasing peaks.
We have studied the quantum efficiency of multilayer organic light emitting diodes (OLEDs). Attention is focused on the recombination efficiency and exciton quenching, controlling the performance of highly efficient OLEDs having Alq(3) (Al(III) 8-hydroxyquinoline) as the emissive layer. The kinetics model is extended to account for the image charge effect on the injection and the narrow bandwidths of carriers. An analytical criterion for maximum recombination efficiency at low voltages is found. The analysis of current voltage dependence and quantum efficiency is performed for Al/LiF/Alq(3)/TPD/ITO devices with or without an ultrathin dielectric layer LiF, taking into account the exciton quenching controlled by the boundary Al-Alq(3). We get a reasonable fit for the experimental data and discuss the optimum modifications required to enhance the device performance.
The eigenstates of small radius molecular excitations, coupled by the resonant dipole-dipole interaction, are examined for a system of random resonant centers. Anomalous scaling properties are seen even in the absence of external disordering, i.e. their properties are intermediate between localized and `true' delocalized states. The effective transport properties of excitations can be described in terms of anomalous diffusion, with a distance dependent diffusion coefficient scaling as D approximately 1/R. This anomalous behavior agrees with our simulation of boundary quenching of excitons and with the related experiment on organic light emitting diodes.