On a new mechanism of polariton–polariton scattering

Condensate states of a two-dimensional exciton–polariton system have been considered under the conditions of direct resonant photoexcitation. It has been theoretically predicted that splitting of eigenmodes with orthogonal polarizations leads to the emergence of a new channel of parametric scattering. A polariton condensate spontaneously decays into a set of states in a finite region of the momentum space, thus leading to a strong inhomogeneity in the distributions of the intensity and polarization even in the case of a strictly constant amplitude and zero in-plane momentum of the external field. The new scattering mechanism makes possible self-oscillating and chaotic states of polariton systems.     

Spin-dependent polariton–polariton scattering in planar microcavities

We present a microscopic theory of polariton–polariton (PP) scattering in quantum microcavities, which is developed with allowance for the composite nature of polaritons. Analytical estimations of the effective scattering rate for PP scattering with parallel spin configuration are presented, and the role of dark excitons in the opposite spin configuration is discussed.     

Exciton–polariton condensation

We review, aiming at an audience of final year undergraduates, the phenomena observed in, and properties of, microcavity exciton–polariton condensates. These are condensates of mixed light and matter, consisting of superpositions of photons in semiconductor microcavities and excitons in quantum wells. Because of the imperfect confinement of the photon component, exciton–polaritons have a finite lifetime, and have to be continuously re-populated. Therefore, exciton–polariton condensates lie somewhere between equilibrium Bose–Einstein condensates and lasers. We review in particular the evidence for condensation, the coherence properties studied experimentally, and the wide variety of spatial structures either observed or predicted to exist in exciton–polariton condensates, including quantised vortices and other coherent structures. We also discuss the question of superfluidity in a non-equilibrium system, reviewing both the experimental attempts to investigate superfluidity to date, and the theoretical suggestions of how it may be further elucidated.     

Controllability of shock waves in one-dimensional polariton condensates

In one-dimensional incoherent pumped exciton–polariton condensates, we realize the generation and control of supersonic shock waves. By choosing a suitable initial input wave, we obtain the region of existence of various shock waves as a function of the phase of the initial wave, the coefficient of polariton interaction, the coefficient of the interaction between polariton and reservoir and the condensation rate and intensity of pumping. Using these results, we discuss the effect of different pa...     

Controlled spin pattern formation in multistable cavity–polariton systems

Theoretical studies are performed of planar cavity–polariton systems under resonant optical excitation. We show that if the cavity is spatially anisotropic, the polariton spin is highly sensitive to the pump polarization direction, which can be used to modulate the circular polarization of the output light. In particular, when the right- and left-circular components of the incident wave have equal intensities and mutually opposite angular momenta, the pump has strictly linear yet angle-dependent polarization and as such brings about a periodic angular variation of the polariton spin. Free motion of polaritons is the other factor determining the shape of the cavity-field distribution. Such externally driven and highly tunable spin patterns represent a counterpart of spin shaping in nonresonantly excited Bose–Einstein condensates of cavity polaritons.     

Dielectric-loaded surface plasmon–polariton nanowaveguides fabricated by two-photon polymerization

The design, fabrication, and characterization of dielectric-loaded surface plasmon–polariton nanowave-guides on a gold film are presented. The nanostructures are produced by two-photon polymerization with femtosecond laser pulses, and the minimum ridge height is ∼170 nm. Leakage radiation microscopy shows that these surface plasmon–polariton waveguides are single mode with strong mode confinement at the wavelength of 830 nm. The experimental results are in good agreement with the simulation by the effective-index method.     

Coherent phase contrast imaging of THz phonon–polariton tunneling

We report on coherent spatiotemporal imaging of single-cycle THz waves in frustrated total internal reflection geometry. Our technique yields images of the spatiotemporal electric field distribution before and after tunneling through an air gap in between two LiNbO₃ crystals. Measurements of the reflected and the transmitted THz waveforms for different tunnel distances allow for a direct comparison with results from a causal linear dispersion theory and excellent agreement is found.     

Near-field Moiré effect mediated by surface plasmon polariton excitation

We have demonstrated a surface plasmon polariton mediated optical Moiré effect by inserting a silver slab between two subwavelength gratings. Enhancement of the evanescent fields by the surface plasmon excitations on the silver slab leads to a remarkable contrast improvement in the Moiré fringes from two subwavelength gratings. Numerical calculations, which agree very well with the experimental observation of evanescent-wave Moiré fringes, elucidate the crucial role of the surface plasmon polaritons. The near-field Moiré effect has potential applications to extend the existing Moiré techniques to subwavelength characterization of nanostructures.     

Rogue waves in exciton–polariton condensates under homogeneous pumping

We predict the emergence of rogue wave solutions in one-dimensional exciton–polariton condensates under homogeneous pumping. We model the condensate dynamics in a microwire using the dissipative Gross–Pitaevskii equation for the polariton field, with considers attractive nonlinearity, coupled to the rate equation of the excitonic reservoir density. With the help of the direct ansatz method and similarity transformation, deformed first order rogue wave solutions are constructed and its dynamics analyzed. We show that the deformed rogue wave has a curved background controlled by the pump power and the strength of the nonlinear interaction of polaritons. Moreover, the maximal population of the polaritons appears where high energy of rogue wave is concentrated.     

Half-quantum vortices in exciton–polariton condensates in applied magnetic field

We study the behavior of half-quantum vortices (HQVs) in exciton–polariton condensates in planar semiconductor microcavities in applied magnetic field. Below the critical magnetic field, that is defined by the polariton–polariton interaction constant, the condensate is elliptically polarized and there are two types of HQVs, deep and shallow. They correspond to singularities in majority and minority circular components of the condensate wave function, respectively. The core radius (healing length) of the deep HQVs decreases and the core radius of the shallow HQVs increases with increase of magnetic field. The shallow HQVs disappear and the deep HQVs transform into the integer vortices in the circularly polarized condensate when the applied magnetic field exceeds the critical one.     

Exciton–polariton formation at room temperature in a planar ZnO resonator structure

We show the dispersion of exciton–polaritons in an all oxide planar resonator structure. A quasi-bulk ZnO film acts as active medium and as cavity. The mirrors are made of Bragg reflectors consisting of ZrO₂ and MgO layers. Despite a limited structural perfection, we have observed a giant energy splitting of the exciton–polariton branches of about 78 meV at maximum using reflectivity and photoluminescence measurements.     

Damping of the localized surface plasmon polariton resonance of gold nanoparticles

We report on a strong damping of the localized surface plasmon polariton resonance of gold nanoparticles. The ultra-fast dephasing time of localized surface plasmon polariton resonances in gold nanoparticles was systematically studied as a function of the particle size at a fixed photon energy of h ν=1.85 eV. Dephasing times ranging from T₂^expT_{2}^{\mathrm{exp}} = 5.5 fs to 15.0 fs were extracted and an influence of the reduced dimensions was detected. We have identified two dominant damping mechanisms: the well-known surface scattering and, for the first time, band structure changes. We have quantified the influence of these band structure changes on the optical properties by determining the essential damping parameter A to be A ^exp=0.32 nm/fs.     

Shear Bloch waves and coupled phonon–polariton in periodic piezoelectric waveguides

Coupled electro-elastic SH waves propagating in a periodic piezoelectric finite-width waveguide are considered in the framework of the full system of Maxwell’s electrodynamic equations. We investigate Bloch–Floquet waves under homogeneous or alternating boundary conditions for the elastic and electromagnetic fields along the guide walls. Zero frequency stop bands, trapped modes as well as some anomalous features due to piezoelectricity are identified. For mixed boundary conditions, by modulating the ratio of the length of the unit cell to the width of the waveguide, the minimum widths of the stop bands can be moved to the middle of the Brillouin zone. The dispersion equation has been investigated also for phonon–polariton band gaps. It is shown that for waveguides at acoustic frequencies, acousto-optic coupling gives rise to polariton behavior at wavelengths much larger than the length of the unit cell but at optical frequencies polariton resonance occurs at wavelengths comparable with the period of the waveguide.     

Direct time domain observation of exciton–polariton oscillation in a semiconductor microcavity

We measured temporal evolution of the coherent emission from a semiconductor microcavity by an ac-balanced homodyne detector with high sensitivity and wide dynamic range. The experimental results can be well explained by the coupled exciton–photon model.     

Scattering of a surface plasmon polariton beam by chains of dipole nanoparticles

Scattering and splitting of surface plasmon polaritons (SPPs) by a chain of strongly interacting nanoparticles located near a metal surface are numerically studied. The applied numerical model is based on the Green’s function formalism and point–dipole approximation for scattering by nanoparticles. Dependencies of the splitting efficiency on the inter-particle distance in the chain and on the angle of incidence of the SPP Gaussian beam are considered. It is found that the splitting efficiency depends on the inter-particle distances especially when the angle between the SPP beam and the chain is relatively small. The role of multiple scattering in the SPP splitting by the chains of nanoparticles is also discussed.     

Control of near-field radiative heat transfer via surface phonon–polariton coupling in thin films

The possibility of controlling near-field radiative heat transfer with the use of silicon carbide thin films supporting surface phonon–polaritons in the infrared spectrum is explored. For this purpose, the local density of electromagnetic states is calculated and analyzed within the nanometric gap formed between two SiC films as well as the radiative heat flux exchanged between the thin layers.     

Apertureless SNOM imaging of the surface phonon polariton waves: what do we measure?

The apertureless scanning near-field microscope (ASNOM) mapping of surface phonon polariton (SPP) waves being excited at the surface of the SiC polar crystal at a frequency corresponding to the lattice resonance was investigated. The wave with well-defined direction and source position, as well as a well-known propagation law, was used to calibrate the signal of an ASNOM. An experimental proof is presented showing that the signal collected by the ASNOM in such a case is proportional (as a complex number) to the local field amplitude above the surface, regardless of the tip response model. It is shown that the expression describing an ASNOM response, which is, in general case, rather complicated nonlinear function of a surface/tip dielectric constants, wavelength, tip vibration amplitude, tip shape etc., can be dramatically simplified in the case of the SPP waves mapping in a mid-IR range, due to a lucky combination of the tip and surface parameters for the case being considered. A tip vibration amplitude is much less than a running SPP wave field decay height in a normal direction. At the same time, the tip amplitude is larger than a characteristic distance at which a tip–surface electromagnetic near-field interaction plays a significant role.     

Dielectric loaded surface plasmon polariton properties of the Al_2O_3–Al nanostructure

Surface plasmons(SPs) in ultraviolet(UV) have attracted a great deal of attention because of their emerging applications in energy resources, environmental protection, and biotechnology. In this article, the dielectric loaded surface plasmon polariton(DLSPP) properties of the Al_2O_3–Al nanostructure are investigated theoretically. Sharp SP responses can be obtained in deep UV by setting an insulator grating on the aluminum film. It is found that the height of the grating element,the lattice parameter, and the filling factor can all modulate the DLSPPs of the Al_2O_3–Al nanostructure. We further find that this structure is sensitive to the embedding medium and can serve as a refractive index sensor in the UV region. The corresponding sensitivity increases with the decrease of the filling factor. The Al_2O_3–Al nanostructure may be useful for medical diagnostics and biotechnology in deep UV.     

Direct laser-writing of dielectric-loaded surface plasmon–polariton waveguides for the visible and near infrared

We demonstrate flexible and low-cost fabrication of dielectric-loaded surface plasmon–polariton waveguides. The waveguide structures are fabricated by two-photon polymerization of commercially available, spin-coatable epoxy-based UV-lithographic resist on a metal covered glass slide. The excitation and guiding properties of the plasmonic waveguides are investigated in the far-field at a wavelength of 632.8 nm by imaging the leakage radiation from the waveguide modes. The optimum bending radius for right angle bends is measured to 6 μm providing a transmission of up to 70%. The functionality of more complex Y-splitters is demonstrated.