Polariton dynamics of a disordered three-cavity system of four-level atoms

The effect of disorder in the intensity of the driving laser on the dynamics of a disordered three-cavity system of four-level atoms is investigated. This system can be described by a Bose-Hubbard Hamiltonian for dark-state polaritons. We examine the evolution of the first- and second-order correlation functions, the photon and atomic excitation numbers and the basis state occupation probabilities. We use the full Hamiltonian and the approximate Bose-Hubbard Hamiltonian with uniform and speckle disorder, as well as with different dipole couplings. We find that the results for the two Hamiltonians are in good agreement. We also find that it is possible to obtain bunching and antibunching of the polaritons by varying the dipole couplings and that polaritons can be driven into a purely photonic state by varying the laser intensity.     

Self-trapping phenomenon in exciton-polariton dynamics

The polariton dynamics in a microcavity in the parametric oscillator mode, when two pump polaritons are transformed into signal and idler polaritons and vice versa, has been studied. A nonlinear differential equation is obtained, which describes the temporal evolution of pump-polariton density, the solution of which is expressed in terms of the Jacobi elliptical functions. The amplitude and period of polaritondensity oscillations are determined by the initial polariton densities and the resonance detuning. The possibility of self-trapping in exciton-polariton dynamics is predicted.     

Dispersionless polaritons at symmetrically oriented surfaces of biaxial crystals

A set of dispersion relations is derived for surface polaritons in optically biaxial crystals at the surfaces parallel to the symmetry planes of the permittivity tensor ?. The domains of existence, as well as the sectors of the propagation directions of dispersionless surface polaritons which arise at positive components of the tensor ?, are analyzed. Three nonoverlapping domains of the dielectric-anisotropy parameters where dispersionless polaritons can exist are found for weakly anisotropic crystals. In each of these domains, polaritons exist at two different mutually orthogonal surfaces of the crystal. In optically biaxial crystals, in contrast to optically uniaxial media, polaritons arise not only in positive but also in negative crystals. The evolution of the optical-axis configuration is traced as the anisotropy parameters vary in the domains of existence of polaritons.     

Picosecond spectroscopy of polaritons in anthracene crystals II. Luminescence

The low-temperature luminescence spectrum of anthracene crystals is investigated by applying simultaneous time and frequency resolution. The complicated kinetics of the emission in the polariton bottleneck region reflects directly the evolution and relaxation of the polariton distribution in the crystal. Three distinct relaxation stages are distinguished: (1) the ultrafast decay of initial vibronic excitations, mediated by optical phonons and resulting in a broad distribution of polaritons near the band bottom; (2) the formation of a narrow distribution of polaritons with a characteristic time of 30 ps, which is caused by scattering on acoustic phonons; (3) relaxation through the bottleneck region on a subnanosecond time scale. It is suggested that the polaritons immediately below the resonance frequency are responsible for the observed excitonic energy transfer in anthracene crystals.     

On the type of a phase transition in the system of exciton polaritons in an optical microcavity

The type of a phase transition in the quasi-equilibrium system of exciton polaritons in a two-dimensional optical microcavity has been analyzed. It has been shown that, although the system contains two types of bosons undergoing mutual transformations into each other, only one phase transition to the superfluid state with the quasilong-range order occurs in the two-dimensional system. This phase transition is a Kosterlitz-Thouless phase transition. A new physical implementation—excitons in a photon crystal—has been proposed for the Bose condensation of exciton polaritons. The superfluid properties of the ordered phase are discussed, and the superfluid density and Kosterlitz-Thouless transition temperature have been calculated in the low-density approximation.     

The dynamics of a polariton dimer in a disordered coupled array of cavities

We investigate the effect of disorder in the laser intensity on the dynamics of dark-state polaritons in an array of 20 cavities, each containing an ensemble of four-level atoms that is described by a Bose-Hubbard Hamiltonian. We examine the evolution of the polariton number in the cavities starting from a state with either one or two polaritons in one of the cavities. For the case of a single polariton without disorder in the laser intensity, we calculate the wavefunction of the polariton and find that it disperses away from the initial cavity with time. The addition of disorder results in minimal suppression of the dispersal of the wavefunction. In the case of two polaritons with an on-site repulsion to hopping strength ratio of 20, we find that the polaritons form a repulsively bound state or dimer. Without disorder the dimer wavefunction disperses similarly to the single polariton wavefunction but over a longer time period. The addition of sufficiently strong disorder results in localization of the polariton dimer. The localization length is found to be described by a power law with exponent ? 1.31. We also find that we can localise the dimer at any given time by switching on the disorder.     

Nonlinear Dynamics of Parametric Oscillations of Polaritons in a Microcavity

Optics and Spectroscopy - The dynamics of polaritons in a microcavity in the parametric oscillator mode, when two pump polaritons turn into the signal and idler polaritons and vice versa, has been...     

On the mechanism of the maintenance of Rabi oscillations in the system of exciton polaritons in a microcavity

A physical mechanism of the implementation of undamped Rabi oscillations in the system of exciton polaritons in a semiconductor microcavity in the presence of nonresonant pumping has been proposed. Various mechanisms of the stimulated scattering of excitons from the reservoir have been considered. It has been shown that undamped oscillations of the population of the photon component of the condensate can be caused by the feeding of a coherent Rabi oscillator owing to the pair scattering of excitons from the reservoir to the ground state. The effect should be observed in spite of a more intense relaxation of polaritons of the upper branch observed experimentally.     

Energy relaxation of excitonlike polaritons in semiconductor microcavities: Effect on the parametric scattering of polaritons

Polariton emission in GaAs-based microcavities has been studied under variable conditions, which made it possible to excite (a) polaritons from the upper polariton branch and hot free polaritons and electrons, (b) polaritons from the lower polariton branch (LPB) and localized excitons, and (c) the mixed system. Variation of the excitation conditions leads to substantial differences in the energy distributions of polaritons and in the temperature dependences of polariton emission. It is established that the energy relaxation of resonantly excited LPB polaritons via polariton and localized exciton states at liquid helium temperatures is ineffective. Instead, the relaxation bottleneck effect is suppressed with increasing temperature by means of exciton delocalization (due to thermal excitation by phonons). The most effective mechanism of relaxation to the LPB bottom is via scattering of delocalized excitons on hot free carriers. It is found that the slow energy relaxation of polaritons excited below the free exciton energy can be significantly accelerated at low temperatures by means of additional weak generation of hot excitons and, especially, hot electrons. This acceleration of the energy relaxation of polaritons by means of additional overbarrier photoexcitation sharply decreases the barrier for stimulated parametric scattering of polaritons excited at an LPB inflection point. Therefore, additional illumination can be used to control the polariton-polariton scattering.     

Resonant infrared transmission through SiC films

Resonant transmission through metallic films is observed when a periodic array of holes is drilled. This phenomenon has been attributed to surface plasmon polaritons. We study a similar system made of an array of slits in a SiC film supporting surface phonon polaritons. We find a resonant transmission in the infrared. The role of surface waves is analyzed. We find that surface waves are excited at resonance but are not a necessary condition to obtain a resonant transmission.     

Comparison of the spectra of a blackbody and thermally stimulated surface plasmon polaritons in the infrared range

The emission spectra of thermally stimulated surface plasmon polaritons (thermally stimulated surface plasmon polaritons) and a blackbody have been analyzed and compared, and the temperature dependence of these spectra has been studied. It has been found that the total energy of the entire ensemble of surface plasmons is proportional to the cube of temperature and their spectrum is red-shifted from the blackbody spectrum. It has been shown that the spectrum of thermally stimulated surface plasmon polaritons obeys the Wien’s displacement law, yet with another constant. The fraction of the photon energy of the conducting layer transferred to the surface plasmons has been estimated. It has been demonstrated numerically by the example of a gold layer that this fraction can exceed 10% for a layer thickness of less than 1 mm.     

Multistability of the optical response in a system of quasi-two-dimensional exciton polaritons

The nonlinear dynamic properties of a system of polaritons in a planar semiconductor microcavity under conditions of external coherent photoexcitation have been investigated. It has been shown that the interaction between polaritons with identical projections of the total angular momentum (J _z ) can give rise to multistability of the response of the excited polariton state. As a result, nonequilibrium transitions between different stability branches become possible due to fluctuations or arbitrarily smooth variations of the excitation parameters and occur with abrupt changes in the intensity and optical polarization of the field in the microcavity. It has been demonstrated that a relatively weak attraction between polaritons with opposite total angular momenta J _z leads to a possibility of spontaneously breaking the symmetry of circularly polarized field components in the microcavity under strictly linear (symmetric) polarization conditions of external excitation.     

Spatial coherence properties of surface plasmon investigated by Young's slit experiment

In this Letter, we present an original method to extract the optical properties of surface plasmon polaritons (SPPs) on silver surfaces. A two Young's slit experiment combined with a leakage radiation microscope has been built. By correlating both imagery and coherence measurements on the same area, we are able to address the evolution of the SPP spatial coherence along its propagation. The proposed method could also be useful to explore the properties of complex plasmonic systems.     

Theory of the effect of a dc current on surface polaritons in n-type silicon

A theoretical investigation has been made of the effect of a drift current on surface polaritons in n-type silicon. The current direction is taken to be the same as the propagation direction of the surface polaritons. Retardation is included, but damping is neglected. In obtaining the dispersion relation, the specular-reflection/mirror-image technique of Kliewer and Fuchs is used to handle the boundary conditions. The results indicate that an interaction takes place between the current and polaritons which gives rise to polariton instabilities for certain frequency ranges. These instabilities are a consequence of the presence of the surface.     

银层超透镜光学传递函数的研究

银层超透镜对基于表面等离子体激元的超分辨光刻、 成像和生物传感有着重要作用.利用银层超透镜的光学传递函数详 细研究了银板的表面等离子体激元共振和成像特性, 并利用时域有限差分法计算模拟了银层超透镜的成像过程, 得到与理论推导公式相符合的结果, 证明了光学传递函数的可靠性, 为基于表面等离子体激元的传感器件、 超分辨成像以及辅助增强干涉光刻提供了快速参数优化方法.     

Theory of a Fabry-Perot type interferometer for surface polaritons

A theory of an interferometer for surface polaritons has been developed. Transmission and reflection coefficients have been calculated for surface polaritons crossing in interferometer on a metal surface. Two kinds of interference phenomena have been described. The experimental results by Z. Schlesginer and A.J. Sievers are discussed.     

Second-order time correlations within a polariton Bose-Einstein condensate in a CdTe microcavity

Second-order time correlations of polaritons have been measured across the condensation threshold in a CdTe microcavity. The onset of Bose-Einstein condensation is marked by the disappearance of photon bunching, demonstrating the transition from a thermal-like state to a coherent state. Coherence is, however, degraded with increasing polariton density, most probably as a result of self-interaction within the condensate and scatterings with noncondensed excitons and polaritons. Such behavior clearly differentiates polariton Bose condensation from photon lasing.     

太赫兹表面极化激元

作为束缚于表面或界面的电磁波与极性元激发的耦合模量子,表面极化激元是克服衍射极限的核心物理.在紫外、可见以及近红外波段,表面等离子极化激元展现出了亚波长特性,具有高分辨成像等应用,并发展成为"表面等离子极化激元亚波长光学"学科;在中红外波段,表面声子极化激元发挥着同样的作用.太赫兹波段曾是人类认识的空白区域,近三十年来得以高速发展,其战略意义重大.具有克服衍射极限能力的太赫兹表面极化激元同样是小型化与集成化太赫兹器件,以及太赫兹超高分辨成像的重要物理基础.近几年来,对以石墨烯为代表的二维材料的研究突飞猛进,诞生了"石墨烯表面等离子极化激元亚波长光学"这门学科,并贡献于太赫兹领域.本文对可在太赫兹波段工作的人工超构材料、掺杂半导体、二维电子气、二维材料、拓扑绝缘体等结构材料的表面极化激元进行了较为全面的总结与介绍,为研制克服衍射极限的太赫兹集成光子学器件提供可资借鉴的物理基础.     

Bose-einstein condensation of exciton polaritons in high-<Emphasis Type="Italic">Q</Emphasis> planar microcavities with GaAs quantum wells

Condensation of exciton polaritons in planar microcavities with GaAs/AlAs quantum wells in the active area has been studied. It has been found that an increase in the lifetime of polaritons up to ∼10–15 ps when the Q factor of a microcavity exceeds 7000 makes it possible to detect Bose-Einstein condensation of polaritons with a dominant (>90%) photon component. Condensation occurs under thermodynamically nonequilibrium conditions in lateral traps with diameters ∼10 μm formed due to long-range fluctuations of the polariton potential. The violet shift of the polariton emission line at the condensation threshold significantly exceeds the energy of the repulsive interaction between polaritons in the condensate. It has been shown that the shift is mainly due to a decrease in the oscillator strength of bright excitons in lateral traps, caused by the localization of photoexcited long-living dark excitons.     

Soliton instabilities and vortex street formation in a polariton quantum fluid

Exciton?polaritons have been shown to be an optimal system in order to investigate the properties of bosonic quantum fluids. We report here on the observation of dark solitons in the wake of engineered circular obstacles and their decay into streets of quantized vortices. Our experiments provide a time-resolved access to the polariton phase and density, which allows for a quantitative study of instabilities of freely evolving polaritons. The decay of solitons is quantified and identified as an effect of disorder-induced transverse perturbations in the dissipative polariton gas.