Properties Of Polaritons Research Articles

Statistics of polaritons in the nonlinear regime

We discuss the quantum statistical properties of exciton polaritons in semiconductor microcavities. The nonlinear dynamics is treated within a model of interacting bosons for the signal, pump, and idler modes. We focus on the regime of parametric amplification below threshold. We present the time evolution of the signal and idler modes towards their stationary solutions and discuss their statistical properties. In particular, we evaluate the amount of squeezing of the radiation emitted out of the microcavity in a configuration, which may be relevant for experiments.

Polaritons in microcavities containing a two-dimensional electron gas

We review the spectroscopic and dynamic properties of cavity polaritons in a λ-wide GaAs/GaAlAs microcavity (MC) structure having a single GaAs/AlAs quantum well in which a variable density two-dimensional electron gas (2DEG) is photoexcited, with a density in the range 0 < ne < 5 × 1011 cm−2. The main observed effects that will be discussed here are: (a) photoexcitation of negatively charged polaritons. These polaritons result of the coupling of the MC photon and the negatively charged excitons. They appear at low temperatures (T <25 K), in the range of low 2DEG densities (ne < 5 × 1010 cm−2), and their coupling strength increases as √ne. (b) The effect of electron–polariton scattering on the polariton spectral linewidth, its complex dependence on the detuning energy, and the electron-induced transition from strong to weak coupling regimes, as ne increases. (c) The efficient polariton transfer across the relaxation bottleneck in the lower branch induced by electron–polariton scattering, and the resulting non-linear dependence of the polariton photoluminescence intensity on ne.

Photoluminescence emission and Raman scattering polarization in birefringent organic microcavities in the strong coupling regime

We have investigated the polarization properties of photoluminescence and Raman scattering in strongly coupled organic microcavities containing cyanine dye J aggregates. The birefringence of radially aligned J aggregates results in a large energy splitting of polariton modes when the electric field of the incoming laser light is perpendicular or parallel to the alignment direction. This splitting allows the degree of polarization of doubly resonant Raman processes involving the vibrational modes of J aggregates to be controlled, where the ingoing and outgoing channels are in resonance with the lower polariton branch. As well as providing insight into the properties of polaritons in organic microcavities, these experiments are a sensitive probe of alignment effects arising during the spin-coating deposition process.

Cavity polaritons in microcavities containing disordered organic semiconductors

Many organic materials (disordered and crystalline as well) have rather broad and dispersionless electronic resonances. The excitations in these materials are localized, and thus for these excitations the wave vector is not a ``good'' quantum number. We analyze the optical properties of exciton polaritons in a microcavity, which utilize such organic materials as the optically active semiconductor. We show that as a result of strong light-matter coupling two polariton branches appear in the microcavity, which are analogous to the cavity-polariton branches observed in inorganic semiconductor structures. However, in contrast to the case of polaritons in inorganic semiconductors, the lower polariton branch exists only in a certain restricted intervals of wave vector values. We also show that in such materials the majority of the electronic excited states do not strongly couple to the cavity photon, and these states can be regarded as essentially incoherent. Applying this physical picture for the microcavities containing disordered cyanine dye J aggregates, we examine the decay of the upper cavity polaritons accompanied by the emission of an intramolecular phonon. We show that the main contribution to the upper polariton nonradiative decay rate arises from the transition to incoherent states, and the transition is very fast (of the order of 50 fs). From the results of our calculations we discuss the dynamics of excitations in a microcavity containing organic materials

Exciton polariton including continuum states: Microscopic versus additional boundary conditions

An exact method, based on microscopic boundary conditions, is developed for calculation of the optical properties of exciton polaritons with spatial dispersion. The method is formulated in a general manner for an arbitrary electron-hole potential and probed in the approximation of the one-dimensional contact interaction, in half-space and slab geometries. Another approach, based on approximate boundary conditions applied to all exciton bound and scattering states, generalizes the concept of additional boundary conditions. This approach yields analytical results for semi-infinite semiconductors and semiconductor slabs and allows us to extract and analyze the contribution of the exciton continuum states to the optical spectra of semiconductors. A correlation between reflectivity and transmission calculated in two different approaches demonstrates the crucial role of the strict boundary conditions in the correct computation of optical spectra.

Direct visualization of the Gouy phase by focusing phonon polaritons.

We report the generation of aberration-free cylindrical phonon-polariton wave packets in uniaxial LiTaO3 crystals by nonresonant impulsive stimulated Raman scattering. The unique properties of phonon polaritons with a typical carrier frequency in the THz regime allow direct measurement of the spatiotemporal amplitude and phase distributions. We demonstrate that under these conditions the phase anomaly (Gouy phase) may be visualized directly through spatiotemporal imaging as the cylindrical wave propagates through its focus.

Peculiarities of Exciton-Polaritons in GaN at Different Polarizations Studied by ?-Photoluminescence Spectroscopy

We report on polariton properties in high quality thick GaN grown by hydride vapor phase epitaxy on c-sapphire. A strong line is observed in the vicinity of the A exciton in π-polarization ( k ⊥ c, E parallel to the c-axis) by micro-photoluminescence (μ-PL). Comparison of the μ-PL and μ-reflectance spectra confirms the internal origin of the polariton emission. In the samples with low density of residual donors the enhancement of the π-polarized component is induced mostly by interbranch scattering which occurs, possibly, due to the complex structure of the exciton–polariton branches at k ⊥ c. The Γ1–Γ5 exciton splitting in the C band is determined by the μ-reflectance as ∼1 meV.

Peculiarities of Exciton–Polaritons in GaN at Different Polarizations Studied by μ-Photoluminescence Spectroscopy

We report on polariton properties in high quality thick GaN grown by hydride vapor phase epitaxy on c-sapphire. A strong line is observed in the vicinity of the A exciton in π-polarization ( k ⊥ c, E parallel to the c-axis) by micro-photoluminescence (μ-PL). Comparison of the μ-PL and μ-reflectance spectra confirms the internal origin of the polariton emission. In the samples with low density of residual donors the enhancement of the π-polarized component is induced mostly by interbranch scattering which occurs, possibly, due to the complex structure of the exciton–polariton branches at k ⊥ c. The Γ1–Γ5 exciton splitting in the C band is determined by the μ-reflectance as ∼1 meV.

Thickness dependence of exciton and polariton spectra from ZnSe films grown on GaAs substrates

ZnSe films with thicknesses from 0.05 to 1.45 μm were grown on GaAs substrates by molecular beam epitaxy. Low temperature photoluminescence (PL) and reflectance spectra are presented to show the thickness dependence of the exciton and polariton properties in the films. In addition to sharp PL peaks from free and donor bound excitons, an acceptor bound exciton peak was observed in the thin films and its intensity decreases rapidly with the film thickness. The PL characteristics show the acceptor centers being the defect states near the ZnSe/GaAs interface. The classical theory of exciton–polaritons was used to calculate the reflectance spectra and compared to the measured results. The comparison reveals the effects of strain, surface, and interface on the reflectance spectra from both heavy- and light-hole excitons. In addition to the strain-induced light- and heavy-hole splitting, the light-hole excitons show a larger damping and less sensitivity to the surface dead layer than the heavy-hole excitons. When the film thickness increases, the interference effects become more important and the contribution from the excited exciton states to the reflectance spectra may no longer be negligible.

Specific heat properties of polariton modes in quasicrystals

We investigate the thermodynamical properties of plasmon polaritons that propagate in multiple semiconductor layers arranged in a quasiperiodical fashion. This quasiperiodicity can be of the so-called deterministic (or controlled) disorder type, i.e., they are neither random nor periodic. Also, they are characterized by the nature of their Fourier spectrum, which can be dense pure point (Fibonacci sequence) or singular continuous (Thue-Morse sequence). The sequences are described in terms of a series of generations that obey peculiar recursion relations. We present both analytical and numerical studies on the temperature dependence of the polariton's specific heat associated with the generation number $n=1,2,3,\dots{}$ for their multiscale fractal energy spectra. We show that when $\stackrel{\ensuremath{\rightarrow}}{T}0,$ the specific heat displays oscillations and when $\stackrel{\ensuremath{\rightarrow}}{T}\ensuremath{\infty},$ the specific heat goes to zero with ${T}^{\ensuremath{-}2}$ (because the energy spectrum considered is bounded).

Many-Body Effects in the Polariton Properties of Semiconductors

Many-body effects between excited carriers are demonstrated to be responsible for the behavior of intensity and phase of the transmitted light in pulse propagation experiments. The optical response is described by a Bethe-Salpeter equation including the renormalization of interband selfenergy and of Coulomb interaction as the two relevant many-body effects. In contrast to previously used quasi-particle approximations these two-particle properties have to be taken into account in dependence on both wave number and energy to give a appropriate description of the spectral properties of excitonic polaritons. Furthermore the interplay with corresponding one-particle properties of the carriers is discussed.

Many-Body Effects in the Polariton Properties of Semiconductors

Many-body effects between excited carriers are demonstrated to be responsible for the behavior of intensity and phase of the transmitted light in pulse propagation experiments. The optical response is described by a Bethe-Salpeter equation including the renormalization of interband selfenergy and of Coulomb interaction as the two relevant many-body effects. In contrast to previously used quasi-particle approximations these two-particle properties have to be taken into account in dependence on both wave number and energy to give a appropriate description of the spectral properties of excitonic polaritons. Furthermore the interplay with corresponding one-particle properties of the carriers is discussed.

Polaritons in uniaxial materials propagating in hollow cylinders.

The properties of polaritons propagating in hollow dielectric and magnetic cylinders embedded in an optically inert medium are studied. We pay special attention to those solutions of Maxwell's equations that give the behavior of the nonradiative modes (confined and localized) propagating in an optically active cylindrical medium. The dispersion relation of surface (localized) modes is obtained. Numerical results are presented for cylinders constituted by magnetic and dielectric materials, such as the uniaxial Heisenberg antiferromagnet MnF2 and the dielectric TiO2.

Effect of dissipation on the properties of surface polaritons in GaAs/AlGaAs heterojunctions in a quantizing magnetic field

A study is reported of nonradiative surface and bulk polaritons in GaAs/AlxGa1−x As real heterojunctions under conditions favoring integer-quantum Hall effect (IQHE) and in the presence of dissipation in a two-dimensional electron layer. The conditions of their existence, the spectrum, and damping have been determined. It is shown that under IQHE conditions all aspects of surface and bulk polaritons are quantized. It is found that, as the wave number is varied, surface and bulk polaritons can transform continuously into one another. The possibilities of experimental observation of nonradiative polaritons are discussed.

Polaritons in anisotropic materials with cylindrical geometry

The properties of polaritons propagating in an anisotropic material with a cylindrical geometry are studied. Solving Maxwell's equations for nonradiative modes, the dispersion relation, power flows, energy densities, and the group velocity of the polaritons are obtained. It is shown that the nonradiative modes can propagate in two different modes namely confined or localized modes. The significative differences between these modes are presented. The uniaxial Heisenberg antiferromagnet ${\mathrm{MnF}}_{2}$ is used in order to obtain numerical results.

Strong coupling of exciton-polaritons in semiconductor microcavities

The most important features of the physics of microcavity-embedded quantum wells are reviewed, with particular attention to the optical properties of exciton polaritons. The strong coupling regime, in which a finite polariton mode splitting appears (also called Rabi splitting), is studied. The problem of including both homogeneous and inhomogeneous broadening effects is addressed. The effects of exciton-phonon interaction and the polariton homogeneous broadening are briefly discussed. The influence of the quantum well in-plane disorder on the spectra of strong coupling samples is then investigated in order to understand the features of the inhomogeneous broadening of the polariton spectrum. Polaritons in low disorder heterostructures display a spectral narrowing, with respect to the ideal case in absence of disorder. This effect is markedly present in state-of-the-art samples. A simplified model of microcavity polaritons which takes into account the quantum well interface roughness is presented. The results provide a satisfactory explanation of recently observed data in terms of multiple scatterings of polaritons on the quantum well disordered potential.

Dielectric Function Theory Calculations of Polaritons in GaN

Properties of polaritons (free excitons coupled with photons of similar energy) in gallium nitride are investigated by performing calculations based on dielectric function theory including all three excitons A, B and C (char- acteristic for the wurtzite structure). Moreover the excited states of excitons have been taken into account by adding Elliott's components to dielectric function. Energies, polarizabilities and damping constants of excitons are determined. It is shown that due to inter-exciton interactions the B and C excitons are strongly damped. It is estimated that the characteristic time of B to A relaxation is tBA = 1 ps. The exciton C lifetime is estimated τc= 0.2ps.

Numerical algorithms for modeling hybrid surface plasmon polaritons guided by metal films

This paper presents an application of the numerical algorithms, based on Davidenko's method. The method has been found to be an efficient technique used to model the properties of hybird surface plasmon polaritons guided by an ultra-thin metal film. A general computer program capable of providing the modeling of the mode effective index and the propagation loss (normalized attenuation constant) is written and implemented. Davidenko's algorithms allows us to obtain accurate numerical results in a very reasonable CPU time. The presented results could be useful in designing guided-wave photonic devices based on materials with relatively large absorptive losses. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 122–124, 1997.

Simulation of radiation effects on three-dimensional computer optical memories.

A model was developed to simulate the effects of heavy charged-particle (HCP) radiation on the information stored in three-dimensional computer optical memories. The model is based on (i) the HCP track radial dose distribution, (ii) the spatial and temporal distribution of temperature in the track, (iii) the matrix-specific radiation-induced changes that will affect the response, and (iv) the kinetics of transition of photochromic molecules from the colored to the colorless isomeric form (bit flip). It is shown that information stored in a volume of several nanometers radius around the particle's track axis may be lost. The magnitude of the effect is dependent on the particle's track structure.

The effective-medium theory of magnetoplasma superlattices

The expression for the effective-medium dielectric tensor of a superlattice in which the dielectric tensors of the constituent media are taken in general form (all elements non-zero) is employed to describe a plasma/non-plasma, e.g. doped/undoped semiconductor superlattice in a magnetic field B0 at an arbitrary angle to the interface. The properties of surface polaritons are discussed in detail for the perpendicular (B0 normal to interfaces) and Faraday (B0 parallel to interfaces, propagation vector along B0) configurations.