Ensemble Of Emitters Research Articles

Influence of localized surface plasmon in a lens-shaped metal cluster on the decay dynamics of a point-dipole emitter

Influence of localized surface plasmon in a lens-shaped metal nanoparticle on the decay dynamics of a point-dipole emitter was studied by means of numerical simulations. Dependencies of radiative and nonradiative decay rates on the distance between the particle and the dipole were calculated for dipole and quadrupole plasmon modes. The presence of the etching cone changes the nonradiative dynamics of a dipole located under a metal cluster and can be a convenient tool to reduce the surface influence on emitters. The cone also selectively enhances the nonradiative decay rate for the emitter located under the vertex enabling preferential plasmon coupling in ensembles of emitters.

Induced -cooperative phenomenon in an ensemble of the nonlinear coupled oscillators

Abstract In the article the cooperative N 2 -effect is considered, that is the radiation whose power is ∼ N 2 , where N is the number of emitters which in this case is equal to the number of nonlinear coupled oscillators. They model the electrons moving in a semiconductor structure with grating (micro-undulator). The suggested effect is in a sense similar to Dicke superradiance, however it is not the spontaneous phase coherence arising in the ensemble of two-level atoms interacting via the emitted electromagnetic field, but rather, the result of interplay of two effects. The first one is the ‘pumping wave’ acting on the electrons and which is the result of undulator field, while the second is the backward effect of radiation which is produced by electrons moving within such micro-undulator. As a result, the specific phase coherence (‘synchronization’) develops in the ensemble of emitters and they start to generate as a single oscillating charge Ne, while the power of emitted radiation becomes ∼ N 2 . It is very probable, that the effect can be used for the developing of a new semiconductor-based room temperature source of the GHz and THz-radiation.

Theory of strong coupling between quantum emitters and propagating surface plasmons.

Here we present the theoretical foundation of the strong coupling phenomenon between quantum emitters and propagating surface plasmons observed in two-dimensional metal surfaces. For that purpose, we develop a quantum framework that accounts for the coherent coupling between emitters and surface plasmons and incorporates the presence of dissipation and dephasing. Our formalism is able to reveal the key physical mechanisms that explain the reported phenomenology and also determine the physical parameters that optimize the strong coupling. A discussion regarding the classical or quantum nature of this phenomenon is also presented.

Scattering of massless particles in one-dimensional chiral channel

We present a general formalism describing the propagation of an arbitrary multi-particle wave packet in a one-dimensional multimode chiral channel coupled to an ensemble of emitters which are distributed at arbitrary positions. The formalism is based on a direct and exact resummation of a diagrammatic series for the multi-particle scattering matrix. It is complementary to the Bethe Ansatz approach and to approaches based on equations of motion, and it reveals a simple and transparent structure of scattering states. In particular, we demonstrate how this formalism works on various examples, including the scattering of one- and two-photon states off two- and three-level emitters, off an array of emitters, as well as the scattering of coherent light. We argue that this formalism can be used constructively for the study of the scattering of an arbitrary initial photonic state off emitters with an arbitrary degree of complexity.

Strongly coupling a cavity to inhomogeneous ensembles of emitters: Potential for long-lived solid-state quantum memories

We investigate theoretically the coupling of a cavity mode to a continuous distribution of emitters. We discuss the influence of the emitters' inhomogeneous broadening on the existence and on the coherence properties of the polaritonic peaks. We find that their coherence depends crucially on the shape of the distribution and not only on its width. Under certain conditions the coupling to the cavity protects the polaritonic states from inhomogeneous broadening, resulting in a longer storage time for a quantum memory based on emitter ensembles. When two different ensembles of emitters are coupled to the resonator, they support a peculiar collective dark state, which is also very attractive for the storage of quantum information.

Correlation between emission intensity of self-assembled germanium islands and quality factor of silicon photonic crystal nanocavities

We present a comparative micro-photoluminescence study of the emission intensity of self-assembled germanium islands coupled to the resonator mode of two-dimensional silicon photonic crystal defect nanocavities. The emission intensity is investigated for cavity modes of L3 and Hexapole cavities with different cavity quality factors. For each of these cavities many nominally identical samples are probed to obtain reliable statistics. As the quality factor increases we observe a clear decrease in the average mode emission intensity recorded under comparable optical pumping conditions. This clear experimentally observed trend is compared with simulations based on a dissipative master equation approach that describes a cavity weakly coupled to an ensemble of emitters. We obtain evidence that reabsorption of photons emitted into the cavity mode is responsible for the observed trend. In combination with the observation of cavity linewidth broadening in power dependent measurements, we conclude that free carrier absorption is the limiting effect for the cavity mediated light enhancement under conditions of strong pumping.

Low-temperature tapered-fiber probing of diamond nitrogen-vacancy ensembles coupled to GaP microcavities

In this work, we present a platform for testing the device performance of a cavity–emitter system, using an ensemble of emitters and a tapered optical fiber. This method provides high-contrast spectra of the cavity modes, selective detection of emitters coupled to the cavity and an estimate of the device performance in the single-emitter case. Using nitrogen-vacancy (NV) centers in diamond and a GaP optical microcavity, we are able to tune the cavity onto the NV resonance at 10 K, couple the cavity-coupled emission to a tapered fiber and measure the fiber-coupled NV spontaneous emission decay. Theoretically, we show that the fiber-coupled average Purcell factor is 2–3 times greater than that of free-space collection, although due to ensemble averaging it is still a factor of 3 less than the Purcell factor of a single, ideally placed center.

Plasmonic Dicke effect

We study cooperative emission by an ensemble of emitters, such as fluorescing molecules or semiconductor quantum dots, near a metal nanoparticle. The primary mechanism of cooperative emission is resonant energy transfer between emitters and plasmons rather than Dicke radiative coupling between emitters. The emission is dominated by three superradiant states with the same quantum yield as a single emitter, leading to a drastic reduction of ensemble radiated energy down to just thrice of that by a single emitter, the remaining energy being dissipated in the metal through subradiant states. We perform numerical calculations of system eigenstates and find that the plasmonic Dicke effect interactions affect is not impacted by the interactions between emitters or non-radiative losses in the metal.

Purcell factor and superradiance in Si-patterned waveguides

Numerical modeling of slotted photonic crystal Si waveguides is reported. Employing multiple slots in a single waveguide, we obtained large Purcell enhancements for a large ensemble of emitters coupled with the same optical mode. This allows observation of peculiar physical phenomena, such as anisotropic bandgap superradiance.

Plasmon-mediated superradiance near metal nanostructures

We develop a theory of cooperative emission of light by an ensemble of emitters, such as fluorescing molecules or semiconductor quantum dots, located near a metal nanostructure supporting surface plasmon. The primary mechanism of cooperative emission in such systems is resonant energy transfer between emitters and plasmons rather than the Dicke radiative coupling between emitters. We identify two types of plasmonic coupling between the emitters, (i) plasmon-enhanced radiative coupling and (ii) plasmon-assisted nonradiative energy transfer, the competition between them governing the structure of system eigenstates. Specifically, when emitters are removed by more than several nm from the metal surface, the emission is dominated by three superradiant states with the same quantum yield as a single emitter, resulting in a drastic reduction of ensemble radiated energy, while at smaller distances cooperative behavior is destroyed by nonradiative transitions. The crossover between two regimes can be observed in distance dependence of ensemble quantum efficiency. Our numerical calculations incorporating direct and plasmon-assisted interactions between the emitters indicate that they do not destroy the plasmonic Dicke effect.

Multicolored devices fabricated by direct lithography of colloidal nanocrystals

Colloidal nanocrystals (NCs) are interesting as potential active medium for novel nanophotonic and nanoelectronic devices, due to their low fabrication costs and full tunability of their opto-electronic properties. In this work we report a multi step approach for the fabrication of multicolored micro- and nano- displays by localizing NCs through lithographic techniques without recurring to etching processes or surface treatment of the substrate. We demonstrate the possibility to localize different ensembles of emitters on the same substrate by realigned photolithographic steps or mix-and-match electron beam and photolithographic approaches. Moreover, fine tuning of the overall pixel emission is shown by varying the concentration ratio among localized red and green NCs. This technique enables the fabrication of optically pumped colored pixels with very high definition. Our approach combined with advances in NCs-based light emitting diodes technology will enable the electrical injection of advanced micro and nano light sources.

Statistical analysis of time-resolved emission from ensembles of semiconductor quantum dots: Interpretation of exponential decay models

We present a statistical analysis of time-resolved spontaneous emission decay curves from ensembles of emitters, such as semiconductor quantum dots, with the aim of interpreting ubiquitous non-single-exponential decay. Contrary to what is widely assumed, the density of excited emitters and the intensity in an emission decay curve are not proportional, but the density is a time integral of the intensity. The integral relation is crucial to correctly interpret non-single-exponential decay. We derive the proper normalization for both a discrete and a continuous distribution of rates, where every decay component is multiplied by its radiative decay rate. A central result of our paper is the derivation of the emission decay curve when both radiative and nonradiative decays are independently distributed. In this case, the well-known emission quantum efficiency can no longer be expressed by a single number, but is also distributed. We derive a practical description of non-single-exponential emission decay curves in terms of a single distribution of decay rates; the resulting distribution is identified as the distribution of total decay rates weighted with the radiative rates. We apply our analysis to recent examples of colloidal quantum dot emission in suspensions and in photonic crystals, and we find that this important class of emitters is well described by a log-normal distribution of decay rates with a narrow and a broad distribution, respectively. Finally, we briefly discuss the Kohlrausch stretched-exponential model, and find that its normalization is ill defined for emitters with a realistic quantum efficiency of less than 100%.

Modification of spontaneous emission in Bragg onion resonators

We formulated an analytical model and analyzed the modification of spontaneous emission in Bragg onion resonators. We consider both the case of a single light emitter and a uniformly distributed ensemble of light emitters within the resonator. We obtain an expression for the average radiation rate of the light emitters ensemble and discuss the modification of the average radiation rate as a function of cavity parameters such as the core radius, the number of Bragg cladding layers, the index contrast of the Bragg cladding, and the refractive index of surrounding medium. We also consider the possibility of non-exponential decay of the light emitter ensemble due to the strong dependence of spontaneous emission on the location and polarization of individual light emitter. We conclude that Bragg onion resonators can both enhance and inhibit spontaneous emission by several orders of magnitude. This property can have significant impact in the field of cavity quantum electrodynamics (QED).

Nonlinear Response of Ozone to Emissions: Source Apportionment and Sensitivity Analysis

For secondary air pollutants, precursor emissions may impact concentrations in nonlinear and interdependent manners. We explore the nonlinear responses of one such pollutant, ozone, to emissions of its precursors, nitrogen oxides (NOx) and volatile organic compounds. Modeling is conducted for a high ozone episode in the southeastern United States, applying a second-order direct sensitivity method in a regional air quality model. As applied here, the sensitivity method neglects most aerosol and aqueous chemistry processes. Inclusion of second-order sensitivities is shown to enable accurate characterization of response to large perturbations in emissions. An index is introduced to characterize the nonlinearity of ozone response to NOx emitted from each source region. Nonlinearity is found to increase with the tonnage and emission density of the source region. Interactions among the impacts of emission sources are shown to lead to discrepancies between source contribution attributed to an ensemble of emitters and the sum of the contributions attributed to each component. A method is introduced for applying these "cross-sensitivity" interactions to assess the uncertainty of sensitivity and source apportionment estimates arising from uncertainty in an emissions inventory. For ozone response to NOx, underestimates in emission rates lead to underprediction of total source contribution but overprediction of per-ton sensitivity.

The multicore fiber – a novel design for a diode pumped fiber laser

A multicore fiber serving as the gain medium for a fiber laser is introduced. Nearly 40 monomode cores are fitted into a standard multimode silica glass fiber. The cores are arranged on an annulus situated near the border of the fiber. The multimode fiber guides the pump radiation with which the Nd 3+-doped cores are excited. The pump waveguide was modelled presupposing that the absorption is nearly homogeneously distributed. The lasing properties of this sophisticated design are quite promising giving about 450 mW at λ=1050 nm for a pump power ( λ=805 nm) of 1800 mW and a fiber length of 40 cm. The slope efficiency amounts to 40%. The far field intensity pattern possessing an angular width defined by a single source resembles that of an ensemble of emitters with random phases.