Interaction between dual cavity modes in a planar photonic microcavity

Abstract

We theoretically study the interaction between dual cavity modes in a planar photonic microcavity structure in the optical communication wavelength range. The merging and splitting of cavity mode is analysed with realistic microcavity structures. The merging of dual cavity resonance into a single cavity resonance is achieved by changing the number of layers between the two cavities. The splitting of single cavity resonance into dual cavity resonance is obtained with an increase in the reflectivity of mirrors in the front and rear side of the microcavity structure. The threshold condition for the merging and splitting of cavity mode is established in terms of structural parameters. The physical origin of the merging of dual cavity modes into a single cavity resonance is discussed in terms of the electric field intensity distribution in the microcavity structure. The microcavity structure with dual cavity modes is useful for the generation of entangled photon pairs, for achieving the strong-coupling regime between exciton and photon and for high-resolution multi-wavelength filters in optical communication.     

Efficiency of spontaneous emission from planar microcavities

Abstract

We use a computational model to investigate the different routes by which power is lost by an optical emitter placed in a microcavity environment. We make a quantitative investigation of the 1/2n ² model used by many workers in evaluating the fraction of power radiated from a thin film of emitting material. We show the limitations of the 1/2n ² model, emphasizing the important role of the orientation of the dipole moment of the emitters. Multi-layer systems, involving dielectric Bragg stack reflectors and metal mirrors, are compared for their efficiency in producing useful radiation. We consider both a standard Bragg reflector and the recently developed omni-directional Bragg stack. We show that metal mirrors, although lossy, may still be effective for producing useful radiation from microcavities. We focus our attention on parameters appropriate for organic microcavity light emitting diode structures.     

Low-threshold lasing and broad-band multiphoton-excited light emission from Ag aggregate-adsorbate complexes in microcavity

A novel class of composites for optics, microcavities doped with metal fractal aggregates, is studied. Lasing and broad-band Stokes and anti-Stokes emission from (Ag colloidal aggregates)/(adsorbed molecules)/(micro-cavity) composite at low-intensity cw and pulse laser excitation has been found. At 633 nm cw excitation wavelength the emission spectrum contains many peaks, spanning a range from wavelength 200 nm to 800 nm. Experiments with pulse excitation of Ag/dye/microcavity composite show that the duration of the observed broad-band anti-Stokes emission significantly exceeds the pump pulse duration, dye molecule fluorescence time, and relaxation times in silver particles. It may be interpreted as a luminescence governed by long-living triplet states of dye molecules. These observations were made possible by use of a fractal-microcavity composite, where coupling the localized plasmon modes in fractal aggregates with microcavity resonances is provided. The important role of multiphoton resonant transitions between discrete states of a finite-size metal particle in enhanced local fields is shown. Analysis, based on the model of a spherical potential well, shows that the observed spectra contain fingerprints of the quantum size effect.     

Spontaneous emission from a three-level atom in two-band photonic crystals

Abstract

We investigate the spontaneous emission from a V three-level atom embedded in two-band isotropic photonic crystals. The dipoles of the two transitions from the two upper levels to the lower level are parallel. Due to the quantum interference between the two transitions and the existence of two bands, the populations in the upper levels display some novel properties, such as anti-trapping and continuous oscillation, which differ from that of a two-level atom (with two bands) and also differ from that if only one band (for three-level atom) is considered. The spontaneous emission field is composed of two parts: localized field and travelling field. The localized field is composed of one or two localized modes, and the travelling field is composed of no, one, two or three propagating modes depending on different conditions. The conditions for different combinations of localized modes and propagating modes are discussed.     

Photoluminescence intermittency of InGaAs/GaAs quantum dots confined in a planar microcavity

Photoluminescence intermittency, or "blinking", was observed in semiconductor InGaAs/GaAs quantum dots (QDs) inside a planar microcavity. Most of the blinking QDs were found around defect sites such as dislocation lines naturally formed in the GaAs barrier layers, and the carrier traps responsible for blinking had an excitation threshold of approximately 1.53 eV. The blinking properties of epitaxial QDs and colloidal nanocrystal QDs were also compared by performing laser intensity dependent measurements and statistics of the "on" and "off" time distributions.     

Spontaneous emission into planar multi-dielectric microcavities: Theoretical and experimental analysis of rare earth ion radiations

Spontaneous emission control for rare earth ions implanted inside planar multidielectric microcavities is investigated theoretically and experimentally. Rigorous classical electrodynamics analyses are presented and compared in order to compute the electromagnetic power provided by sources located inside planar dielectric multilayer structures. Radiation patterns and lifetime measurements are performed in Ta₂O₅/SiO₂ microcavities implanted with erbium and praseodymium ions. Although we demonstrate a significant enhancement of the spontaneous emission in a direction normal to the layer (up to 30%), we show that a large amount of the emitted power is carried by the guided modes of the structures.     

Spontaneous emission from a double V-type four-level atom in a double-band photonic crystal

Abstract

Quantum interferences in spontaneous emission from a double V-type four-level atom in a double-band photonic crystal have been investigated. The double V-type transitions from the two upper levels to the two lower levels can interact not only with modes near the edges of a double-band photonic band gap, but also with free vacuum modes. The resulting two types of quantum interferences give rise to not only dark lines, but also a narrow spontaneous line in the spectrum from the transition coupled to the free vacuum modes. The dark lines and narrow spontaneous line are shown to be dependent on the width of the forbidden gap, relative position of the upper levels from the band edges, coupling constants, and initial coherent superposition state of the system.     

Spontaneous emission from the C3 radical in carbon plasma

Spontaneous emission measurements are discussed for the Swings transitions of the C(3) radical in laser-generated graphite plasma, and the spectroscopy of the C(3) radical in carbon vapor and plasma is summarized. A review is given of some theoretical calculations and emission spectroscopic investigations are presented. Time-averaged, laser-induced optical breakdown spectra are reported from Nd:YAG laser generated graphite microplasma. In 200-300 Torr of argon and helium, and depending on the specific experimental configuration, a weak emission continuum is observed centered at 400 nm when using a laser fluence of typically 1 J/cm(2). Such continua were not detected in our previous experiments using focused laser radiation. The possibilities for the origin of this continuum are considered.     

Spin-resolved Purcell effect in a quantum dot microcavity system

We demonstrate the spin selective coupling of the exciton state with cavity mode in a single quantum dot (QD)-micropillar cavity system. By tuning an external magnetic field, each spin polarized exciton state can be selectively coupled with the cavity mode due to the Zeeman effect. A significant enhancement of spontaneous emission rate of each spin state is achieved, giving rise to a tunable circular polarization degree from -90% to 93%. A four-level rate equation model is developed, and it agrees well with our experimental data. In addition, the coupling between photon mode and each exciton spin state is also achieved by varying temperature, demonstrating the full manipulation over the spin states in the QD-cavity system. Our results pave the way for the realization of future quantum light sources and the quantum information processing applications.     

Light emission from sources located within metallodielectric planar microcavities

A simple, rigorous electromagnetic formula is derived for predicting the electromagnetic power provided by sources located in transparent or dissipative planar microcavities. With this simple approach, we compare numerically and experimentally the electromagnetic power that escapes the microcavity when the source is located in a metallodielectric or in an all-dielectric resonant planar structure. Although a strong light-extraction coefficient might be expected for metallodielectric microcavities, we show that these attractive structures suffer from metal absorption even when thin metallic layers are used. Experiments implemented with europium chelates located in metallodielectric or in all-dielectric microcavities confirm this result.     

Effective optical excitation and resonant luminescence of erbium ions in the spectral region of eigenmodes of a planar microcavity

We report a strong increase in the intensity of spontaneous emission from erbium ions embedded into an active layer of amorphous silicon oxide (a-SiO _x ) in a planar microcavity based on a-Si:H/a-SiO _x layers. Using eigenmodes of this microcavity both for excitation (pumping) and for the extraction of photoluminescence, it is possible to increase the spontaneous emission intensity from erbium ions by a factor of about 500 as compared to the photoluminescence from a single doped a-SiO _x (Er) film.     

Spontaneous emission from a three-level atom placed in three-dimensional photonic crystals in the long-time limit

The paper describes the spontaneous emission from a three-level atom placed in a periodic dielectric microstructure which exhibits a complete three-dimensional photonic band gap. By using the Euler approach, the upper level population of the atom is calculated for a wide range of relationships between the Rabi frequency and the detuning of the atomic transition frequency from the upper band edge. The results indicate that there are three cases of the relationship between Rabi frequency and detuning, which determine distinctive states of the atomic population in the long-time limit. When the detuning is greater than the Rabi frequency, the upper level has a zero steady-state atomic population, which leads to enhancement of spontaneous emission. When the magnitude of the detuning is less than the Rabi frequency, the upper level has a nonzero steady-state atomic population, which leads to suppression of spontaneous emission. When the negative detuning is greater than the Rabi frequency, the upper level has a nondecaying oscillatory-state atomic population due to long-time atomic splitting. These three properties of the spontaneous emission are relevant to several optical devices on an atomic scale, such as optical memories, switches and clocks.     

Spontaneous emission from a three-level atom embedded in anisotropic photonic band gap structures

Abstract

We investigate spontaneous emissions from a three-level atom embedded in realistic anisotropic photonic band gap structures, where the band edge is assumed to be midway between the two upper levels of the atom. In the anisotropic model, the atom-field interaction is reduced to be smaller than that in the ideal isotropic model, which results in the reduction of suppression and oscillation effects in the spontaneous emission; however, we demonstrate that the suppression is strongly enhanced even in the anisotropic model by expanding the detuning between the upper level and the band edge, while the oscillation is greatly reduced. This demonstration is carried out by calculating the atomic state vector for a wide range of the detuning. Using the state vector, the atom-field interaction is studied for two field parts, a localized part and a propagating part, separately. For the localized part, the atom-field interaction is enhanced by expanding the detuning, in spite of the anisotropy, which leads to a strong suppression effect, while for the propagating part, the atom-field interaction is reduced, which leads to a weak oscillation effect. This result is relevant to strong memory effects with high-speed switching, which are attractive properties for a qubit.     

Spontaneous emission from a four-level atom embedded in photonic crystals via quantum interference

The spontaneous emission of a four-level atom embedded in a one-dimensional photonic crystal is investigated. The atom has two upper levels coupled by the same vacuum modes to a common lower level and is driven by a coherent field to an auxiliary level. Spontaneous emission can be suppressed significantly due to the combinational influences of the interference effect and the band edge effect. The radiation field emitted by the atom is also studied. Spontaneous emission can be modified by controlling the Rabi frequency of the driving.     

Coherent state path integral approach to multi-time correlation functions and photon emission in a semiconductor microcavity

In this paper by using the coherent state path integral field theory approach, we calculate the grand canonical partition function of an interacting combined system in the presence of the relevant source terms. It allows us to calculate multi-time correlation functions of interacting systems without using the quantum regression theorem. Then, we investigate the power spectrum and the second-order correlation function of the emitted photons from a microcavity in the presence of excitations of a semiconductor quantum well. By using the Hubbard–Stratonovich transformation, we investigate the effects of reservoir, detuning, the Coulomb interaction and the phase space filling on the power spectrum and the second-order correlation function of the emitted photons.     

Spontaneous emission and cooperative effects near a thin metallic film

The set of surface modes propagating in the plane of a thin metallic film and decaying on both sides of the film provide a relaxation channel for excited electric dipoles in the vicinity of the film. The electric field Green functions associated with these localized modes are derived and used to evaluate the decay rates of a single dipole and of a two-dipole system of parallel or orthogonal dipole orientations. The effects of varying the parameters, namely the metallic film, dipole oscillation frequency and dipole position on the decay characteristics are examined. Unfamiliar pair cooperative quantum effects are pointed out, especially when the two dipoles are at close proximity to each other on the same side of the film, or forming an image configuration in which they are reciprocally located at equal distances on different sides of the film. Possible experiments to explore the predictions of the paper are envisaged to make use of the monolayer assembly techniques with LB films as spacers separating polarized molecular layers on the same side or different sides of the metallic film.     

Theory and simulation of surface plasmon-coupled directional emission from fluorophores at planar structures

A theoretical approach to surface plasmon-coupled emission (SPCE) from planar structures is developed. It is used for simulations. The results are compared to experimental findings. The match is almost perfect concerning emission angles. Power relations and decay times are reproduced qualitatively. The theory is based on Fresnel plane wave refraction at planar multilayered structures and the Weyl identity for expressing the dipolar radiation in terms of plane waves. One-dimensional integrals, used for the numerical computations, are derived for the fields, powers, and decay enhancements. This theoretical approach is shown to be well suited for design of SPCE setups and for prediction and explanation of experimental results. It also shows promise for refinement and optimization of SPCE, concerning enhancement of weak fluorophores, and usage of decay times.     

A threshold electric field for acoustic emission from ferroelectric Rochelle salt

As Rochelle salt is cycled around its ferroelectric loop, copious acoustic emission (AE) is produced, predominantly as the regions of saturation polarisation at the loop extremities are approached. A threshold field for AE has been found, which has been measured throughout the temperature range (?18° to +24°C) in which Rochelle salt is in its ferroelectric state. Near both the lower and upper Curie points the threshold field becomes larger, a finding which is attributed to the higher voltage required to induce the acoustic noise generating processes, namely domain wall nucleation and annihilation, because as each Curie point is approached the domain walls become more mobile.     

Spontaneous and stimulated emission in microwave oscillators with a virtual cathode

A one-dimensional model of electron beam emission with a virtual cathode is used to show that spontaneous emission occurs in a reditron while stimulated emission is observed in vircators and negative triodes. However, at a certain stage in the latter, the radiative instability is quenched as a result of the evolution of turbulence in the electron beam. The idea is therefore put forward that this quenching may be eliminated by specially shaping the leading edge of the high-voltage supply pulse to the diode of the microwave oscillator. Pis’ma Zh. Tekh. Fiz. 24, 41–46 (February 26, 1998)     

Spontaneous emission and lame shift in photonic crystals

Being motivated by the controversial results based on two dispersion models and Weisskopf–Wigner approximation (WWA), we introduce, for the first time to our knowledge, the position-dependent photon-atom interaction into the Green function method of the evolution operator and develop a universal theoretical approach to study spontaneous emission of atoms in photonic crystals (PCs). A position-sensitive generalized Lorentzian formalism (non-Lorentzian shape) for the decay of an excited atom in PCs is derived, and an exact numerical method for calculating the local coupling strength, proportional to the photonic local density of state (LDOS), is presented. For weak interaction PCs with pseudo gaps, the generalized Lorentzian formalism may be reduced to the famous Lorentzian spectrum. In this case, we introduce a lifetime distribution function for an assembly of atoms and find that it depends strongly on the atomic configuration in space, which clarifies successfully the tremendous discrepancy between different experiments. For the PCs with large full gaps, we find that the atomic position can fundamentally change the decay behavior of an excited atom: in strong interaction positions, the atomic decay is non-classical or exhibits an envelope-damped Rabi oscillation, while in weak interaction positions the WWA is valid. Recently, we also predicted giant Lamb shifts for hydrogen atoms in PCs, and revealed that in inhomogeneous electromagnetic environment, the dominant contribution to the Lamb shift comes from real photon emission, while the contribution from emission and reabsorption of virtual photon is negligible, in vast contrast with the case of free space where the virtual photon processes play a key role.