Parametric scattering in a system of quasi-two-dimensional exciton polaritons under photoexcitation near the bottom of the upper polariton branch

Cascade processes of exciton-polariton scattering in a planar semiconductor microcavity taking place under resonance pumping near the bottom of the upper polariton branch are studied theoretically. When the conservation laws allow the decay of the resonantly excited state into two modes that belong to different (the upper and lower) polariton branches, the distribution of scattering directions has the general shape of two rings that correspond to the cross sections of the lower and upper polariton dispersion surfaces by constantenergy planes. Due to the interactions between the particles, instability develops in the system of scattered modes, which is accompanied by marked inhomogeneities in the distribution of the cavity photoluminescence signal. Self-organization in such a system leads to the appearance of solutions of an essentially collective nature. As the critical (threshold) pump power is attained, macroscopic occupancy of a predominant signal mode near the bottom of the lower polariton branch sets in. The characteristics of the signal for different powers and optical polarizations of the pump are analyzed.     

Dynamics of a Spinor Exciton–Polariton System in Laterally Strained GaAs Microcavities under Resonant Photoexcitation

The evolution of the spatial coherence and the polarization has been studied in a freely decaying polariton condensate that is resonantly excited by linearly polarized picosecond laser pulses at the lower and upper sublevels of the lower polariton branch in a high-Q GaAs-based microcavity with a reduced lateral symmetry without excitation of the exciton reservoir. It is found that the condensate inherits the coherence of the exciting laser pulse at both sublevels in a wide range of excitation densities and retains it for several dozen picoseconds. The linear polarization of the photoexcited condensate is retained only in the condensate at the lower sublevel. The linearly polarized condensate excited at the upper sublevel loses its stability at the excitation densities higher a threshold value: it enters a regime of internal Josephson oscillations with strongly oscillating circular and diagonal linear degrees of polarization. The polariton–polariton interaction leads to the nonlinear Josephson effects at high condensate densities. All the effects are well described in terms of the spinor Gross–Pitaevskii equations. The cause of the polarization instability of the condensate is shown to be the spin anisotropy of the polariton–polariton interaction.     

One-dimensional polariton solitons and soliton waveguiding in microcavities

We extend our recent results [O.A. Egorov et al. Phys. Rev. Lett. 102, 153904 (2009)] on half-light–half-matter polariton solitons in planar semiconductor microcavities operating in the strong coupling regime. We initiate discussion on the structure of the solitons in the momentum space and its link to the instability of the upper branch of the polariton bistability loop. Numerical results showing the soliton excitation by a seed pulse are presented.     

Phonon-induced polariton superlattices

We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.     

Quantum degeneracy of microcavity polaritons

We investigate experimentally one of the main features of a quantum fluid constituted by exciton polaritons in a semiconductor microcavity, that is, quantum degeneracy of a macroscopic fraction of the particles. We show that resonant pumping allows us to create a macroscopic population of polaritons in one quantum state. Furthermore, we demonstrate that parametric polariton scattering results in the transfer of a macroscopic population of polariton from one single quantum state into another one. Finally, we briefly outline a simple method which provides direct evidence of the first-order spatial coherence of the transferred population.     

Evolution of surface plasmon–polariton wave in a thin metal film: The modulation‐instability effect

The modulation instability development of intensive surface plasmon–polariton waves in a thin metal film is studied. It is shown both analytically and numerically that the modulation‐instability effect can give rise to spatial redistribution and longitudinal localization of surface plasmon–polariton wave energy on the subwavelength scale. Analytical expressions for the driving parameters of the modulation instability process ? nonlinearity and dispersion ? are derived. The impact of the film thickness and dielectric permittivities of constituents on the dynamics of surface plasmon–polariton wave transformation is considered. Numerical simulations show that in the layer structure comprising a silver film of subwavelength thickness a train of subpicosecond optical pulses with high repetition rate can be generated.

     

Theory of surface polaritons in n-type silicon in the presence of a DC current

A theoretical investigation has been carried out on the effect of a drift current on surface polaritons in n-type silicon. The current direction is taken to be parallel to the direction of propagation of the surface polaritons. From the dispersion curves, there is evidence that an interaction takes place between the current and the polaritons which gives rise to polariton instability or amplification for certain frequency ranges. These instabilities are believed to be due to the presence of the surface.     

On the stability of electromagnetic field in inverted media

The dispersion equation in the problem of electromagnetic field stability in an infinite inverted homogeneous medium is analyzed rigorously. The instability region for small quantum numbers k is established. It is found that, in contrast to the prevailing opinion, a continuous transition is also possible between polariton waves and electromagnetic waves upon a gradual variation of k; in this case, the two types of waves cannot be separated.     

Time resolved scattering relaxation mechanisms of microcavity polaritons

We study the polariton relaxation dynamics for different scattering mechanisms as: Phonon and electron scattering procesess. The relaxation polariton is obtained at very short times by solving the Boltzman equation. Instead of the well-known relaxation process by phonons, we show that the bottleneck effect relaxes to the ground state more efficiently at low pump power intensity when the electron relaxation process is included. In this way, we clearly demonstrate that different relaxation times exist, for which any of these two mechanism is more efficient to relax the polariton population to the ground state.     

Josephson dynamics for coupled polariton modes under the atom–field interaction in the cavity

We consider a new approach to the problem of Bose–Einstein condensation (BEC) of polaritons for atom–field interaction under the strong coupling regime in the cavity. We investigate the dynamics of two macroscopically populated polariton modes corresponding to the upper and lower branch energy states coupled via Kerr-like nonlinearity of atomic medium. We found out the dispersion relations for new type of collective excitations in the system under consideration. Various temporal regimes like linear (nonlinear) Josephson transition and/or Rabi oscillations, macroscopic quantum self-trapping (MQST) dynamics for population imbalance of polariton modes are predicted. We also examine the switching properties for time-averaged population imbalance depending on initial conditions, effective nonlinear parameter of atomic medium and kinetic energy of low-branch polaritons. PACS 03.75.Lm; 71.36.+c; 42.50.Fx     

Polariton trap in microcavities with metallic mirrors

In planar microcavities with metallic mirrors the spectra of cavity polaritons may be strongly modified by the presence of a surface plasmon interacting with transverse-magnetic (TM)-polarized cavity modes. In particular, for certain parameters of the cavity, a minimum in the dispersion of the TM-polarized polariton may develop, which is located in the non-radiative part of the spectrum. This minimum may serve as a very effective trap for polariton population at high non-resonant excitation of the cavity.     

Coherent control of polariton parametric scattering in semiconductor microcavities

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k=0, even for delays much longer than the pulse width. The control of a large population at k=0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the scattering get faster. Just above threshold the parametric scattering process shows unexpected long coherence times, whereas when pump power is risen the contrast decays due to a significant pump reservoir depletion. The weak pulses at normal incidence control the whole angular emission pattern of the microcavity.     

Importance of the polariton viewpoint concerning the exciton luminescence at low temperatures

Large LO-phonon sideband and broad zero-phonon line in the free-exciton luminescence spectra of semiconductors are never explained with the assumption of the thermal equilibrium for excitons especially at low temperatures. They are satisfactorily explained in the polariton framework with polariton accumulation at the bottleneck in polariton decay.     

Room-temperature polariton parametric scattering driven by a one-dimensional polariton condensate

We demonstrate a novel way to realize room-temperature polariton parametric scattering in a one-dimensional ZnO microcavity. The polariton parametric scattering is driven by a polariton condensate, with a balanced polariton pair generated at the adjacent polariton mode. This parametric scattering is experimentally investigated by the angle-resolved photoluminescence spectroscopy technique under different pump powers and it is well described by the rate equation of interacting bosons. The direct relation between the intensity of the scattered polariton signal and that of the polariton reservoir is acquired under nonresonant excitation, exhibiting the explicit nonlinear characteristic of this room-temperature polariton parametric process.     

Dynamics of microcavity polaritons in the Markovian limit

A master equation for the reduced density matrix of the microcavity polaritons coupled with the reservoir of high energy excitons is derived. It is allowed both the polaritons and the excitons to be self-interacting systems. Long time asymptotic properties of the polariton population is studied in the whole range of the reservoir temperatures and the corresponding decoherence effects are reported.     

Quantization of the surface polariton field and the decay of an atom in the presence of a dielectric

The surface polariton field due to the presence of an anisotropic dielectric occupying a semi-infinite domain has been quantized is this letter. The quantized field expressions are used to calculate the probability that an atom in the vicinity of a dielectric decays with the emission of a surface polariton.     

Statistical properties of polariton states

Summary The unitary transformation that relates free polarization and photon states to polariton states is constructed. The time evolution of an arbitrary initial state in terms of the polariton Hamiltonian is presented. The many-photon components of polariton states as well as the transition probabilities to polariton states and the intrinsec and time-dependent polariton squeezing are discussed.     

The influence of critical points on polariton dispersion in the band of two-particle states

The presence of critical points in the two-phonon band in conditions of the Fermi resonance on a polariton may result in a considerable polariton dispersion inside the band of two-particle states. Moreover, the polariton linewidth, conditioned by the decay into two particles, is shown to become zero near critical points; this fact holds certain promise for the determination of the positions of critical points in side the band of two-particle states.     

Optical polariton properties in ZnSe-based planar and pillar structured microcavities

Strong coupling is demonstrated in monolithic ZnSe-based microcavities. Under nonresonant excitation the polariton dispersion has been investigated in dependence on the photon-exciton detuning for different excitation densities at low temperatures. For zero detuning indications of a polariton lasing threshold are observed like a k-space and energy dispersion narrowing of the lower polariton branch with increasing excitation density. Furthermore, it is observed that this effect is hampered for measurements at negative detunings as a result of the less effective polariton relaxation to the ground state. Latter results in the formation of a discrete polariton distribution at finite k values as known for the polariton bottleneck. In order to investigate the influence of a three-dimensional optical confinement on the polariton relaxation, pillar structured microcavities were fabricated. The formation of discrete polariton states in the k-space distribution is observed. Furthermore, indications for a softening of the k-conservation arising from the structural confinement are found leading to a more effective polariton relaxation. This process would be beneficial for the realization of efficient polariton lasing processes.     

Polariton parametric amplifier pump dynamics in the coherent regime

We studied the pump coherent dynamics in a II-VI microcavity parametric amplifier, using angle-resolved four-wave mixing. The polariton parametric amplification is found to result in a strong quenching and saturation of the pump coherence lifetime above the threshold. For the polariton scattering processes that remain below the amplification threshold, we find an angle-dependent collision broadening associated with the efficiency of the polariton scattering towards the excitonic reservoir.