Polariton Model Research Articles

Efficient material treatment by axi-symmetrically polarized laser radiation

Recent years the increased interest is to the problem of interaction of nontraditionally polarized laser radiation with condensed media. The experiments with axisymmetrical polarization attract more attention. The peculiarities of interaction of axisymmetrical laser radiation with condensed matter are considered in framework of universal polariton model. It is shown that more effective is interaction of radially polarized laser radiation with surface active media. The optical schemes for efficient material treatment by radially polarized radiation are sketched.

Simple Model for Gold Nano Particles Concentration Dependence of Resonance Energy Transfer Intensity

Gold nano particles (GNPs) concentration dependence of the energy transfer occurs between the fluorophores and GNPs is investigated. In the case of theses pairs, GNPs can enhance or quench the fluorescence of fluorophores depending upon the relative magnitudes of two energy transfer mechanisms: i) the plasmonic field enhancement at the fluorophores emission frequencies (plasmon coupled fluorescence enhancement) and ii) the localized plasmon coupled Forster energy transfer from fluorescent particles to gold particles, which quenches the fluorescence. The competition of these mechanisms is depending on the spectral overlap of fluorophores and GNPs, their relative concentration, excitation wavelength. Simple two branches surface plasmon polariton model for GNPs concentration dependence of the energy transfer is proposed. The experimental data and theoretical results confirm our findings.

Generalized Bogoliubov Polariton Model: An Application to Stock Exchange Market

A generalized Bogoliubov method for investigation non-simple and complex systems was developed. We take two branch polariton Hamiltonian model in second quantization representation and replace the energies of quasi-particles by two distribution functions of research objects. Application to stock exchange market was taken as an example, where the changing the form of return distribution functions from Boltzmann-like to Gaussian-like was studied.

Topological polaritons with squeezed photons

In this paper, we demonstrate that the topological polaritonic states of a two-dimensional coupled matter–light system can be optically controlled. By introducing a squeezed light field, we generalized the model of topological polaritons, where the matter–light coupling constant winds in momentum space, leading to the nontrivial topology. The bulk excitation spectrum, polariton wave function, topological invariant, and edge mode spectrum are calculated. It is found that mixing the excitons with nonsqueezing photons will result in a time-reversal-symmetry-breaking quantum-spin-Hall-like polaritonic state. However, the quantum-Hall-like state arises when the photonic part of the polaritons is squeezed. Driven by the varying degree of squeezing, there is a topological phase transition with the closing of the bulk excitation gap. Across the phase transition, the direction of edge mode propagation is reversed, which is demonstrated by an edge mode simulation. Such a feature may provide an opportunity for realizing one-way edge channels with adjustable directionality.

Localized surface plasmon polaritons and nonlinear overcoming of the diffraction optical limit

Experimental results on the formation of ordered structures on the surface and in the near-surface layer of condensed media under the action of linearly polarized laser radiation pulses are analyzed. The formation of subdiffraction nanostructure gratings with anomalous orientation is discussed in the context of the universal polariton model. A physical model of the formation of anomalous structure gratings with periods much less than the laser radiation wavelength is proposed and experimentally verified. The model is based on excitation and mutual interference of channel (wedge) surface plasmon polaritons.

Ground-state and spectral signatures of cavity exciton-polariton condensates

We propose a projector-based renormalization framework to study exciton-polariton Bose-Einstein condensation in a microcavity matter-light system. Treating Coulomb interaction and electron-hole/photon coupling effects on an equal footing we analyze the ground-state properties of the exciton polariton model according to the detuning and the excitation density. We demonstrate that the condensate by its nature shows a crossover from an excitonic insulator (of Bose-Einstein respectively BCS type) to a polariton and finally photonic condensed state as the excitation density increases at large detuning. If the detuning is weak polariton or photonic phases dominate. While in both cases a notable renormalization of the quasiparticle band structure occurs that strongly affects the coherent part of the excitonic luminescence, the incoherent wavevector-resolved luminescence spectrum develops a flat bottom only for small detuning.

A functional approach to polariton quantum crystals

We study a generalized Dicke model of polaritons, with a pair-potential interaction between excited states of the spin component, in the functional integral formalism. With a potential that is attractive over a finite momentum range and otherwise repulsive, we determine stability conditions for a spatially homogeneous state. We find that depending on the potential, the interaction may induce an instability in the sound mode of the polariton condensate, or destroy the condensate altogether. In the case of an instability, we study the existence and excitations of weakly periodic states in a triangular lattice.

Plasmonic formation mechanism of periodic 100-nm-structures upon femtosecond laser irradiation of silicon in water

The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon by multiple (N = 100) linearly polarized Ti:sapphire femtosecond laser pulses (duration τ = 30 fs, center wavelength λ0 ∼ 790 nm) is studied experimentally in air and water environment. The LIPSS surface morphologies are characterized by scanning electron microscopy and their spatial periods are quantified by two-dimensional Fourier analyses. It is demonstrated that the irradiation environment significantly influences the periodicity of the LIPSS. In air, so-called low-spatial frequency LIPSS (LSFL) were found with periods somewhat smaller than the laser wavelength (ΛLSFL ∼ 0.7 × λ0) and an orientation perpendicular to the laser polarization. In contrast, for laser processing in water a reduced ablation threshold and LIPSS with approximately five times smaller periods ΛLIPSS ∼ 0.15 × λ0 were observed in the same direction as in air. The results are discussed within the frame of recent LIPSS theories and complemented by a thin film based surface plasmon polariton model, which successfully describes the tremendously reduced LIPSS periods in water.

Periodic nanostructures on titanium dioxide film produced using femtosecond laser with wavelengths of 388 nm and 775 nm.

Titanium dioxide (TiO2) film is an important biomaterial used to improve the biocompatibility of titanium (Ti). We have used a film coating method with an aerosol beam and femtosecond laser irradiation to form periodic structures on biomaterials for control of the cell spreading. The control of cell spreading on biomaterials is important for the development of advanced biomaterials. In this study, nanostructures with periods of 130 and 230 nm were formed on a film using a femtosecond laser with wavelengths of 388 and 775 nm, respectively. The nanostructure period on the film was 30% of the laser wavelengths. Periods produced with wavelengths of 388 and 775 nm were calculated using a surface plasmon polariton (SPP) model and the experimental results for both wavelengths were in the range of the calculated periods, which suggests that the mechanism for the formation of the periodic nanostructures on the film with a femtosecond laser was due to the excitation of SPPs.

Interaction of laser radiation with an axially symmetric polarization with condensed media

The interaction of laser radiation with an axially symmetric polarization with condensed media is studied theoretically. The interaction results in the formation of ordered micro- and nanoscale structures that can be described in terms of the universal polariton model of laser-induced media damage. It is shown that the radially polarized radiation induces a periodic ring resonance grating that focuses the excited surface plasmon-polaritons, thus increasing the total light intensity in the center of the irradiated zone.

Control of terahertz transmission through sub-wavelength copper film gratings deposited on RF-4 substrates

Low cost terahertz filters (copper gratings) have been fabricated by using plastic substrates and printed circuit board processes. The optical properties of these gratings have been investigated. These sub-wavelength copper film gratings with various periods display remarkably enhanced transmission over the terahertz wavelength range. The maximum amplitude transmission efficiency reaches 86% for the grating with a period of 500 μm. The resonance peaks shift to lower frequencies on increasing the period of the gratings. By analyzing three kinds of models, we demonstrate that the excitation of surface plasmons on the upper and lower interfaces of the grating is the prime mechanism responsible for the extraordinary transmission. Various phase shifts between samples and the bare substrate have been detected, leading to the transmission dip frequencies of our experimental results deviating from the theoretical predictions of a surface plasmon polariton model. In addition, apparent angle-dependent behaviors have been observed in the transmission spectra of the grating with the period of 500 μm and the slit width of 180 μm, which confirms that the copper film grating is a promising geometry for producing terahertz polarizers.

Surface plasmon polariton model of high-spatial frequency laser-induced periodic surface structure generation in silicon

In recent years, high-spatial frequency laser-induced surfaces structures have been generated in a large variety of dielectrics. In silicon subwavelength ripples, some of which featured periodicities below 100 nm, were formed using ultrafast lasers. We demonstrate for Si(100) surfaces that generation of a dense electron-hole plasma in the focal spot of ultrashort-pulsed laser light followed by massive excitation of plasma waves provides an explanation for the formation of such high-spatial frequency surface structures. The applied Drude-like model includes carrier-carrier collisions and is in excellent agreement with the experimentally observed ripple period.

Thermal waveguide and fine-scale periodic relief on the semiconductor’s surface induced by TEA CO2 laser radiation

The results of experimental study of linear CO2 laser radiation interaction with semiconductor monocrystals (silicon, germanium, gallium arsenide,) are presented. It was shown that produced surface relief of micro- and nano-structures with spatial periods d ~ ?/n, d ~ ?/2n and d ~ ?/8n (for germanium) are well explained in the framework of universal polariton model of laser-induced condensed-matter damage.

Polariton Mott insulator with trapped ions or circuit QED

We consider variants of the Jaynes-Cummings-Hubbard model of lattice polaritons, taking into account next-nearest-neighbor, diagonal, and long-range photon hopping in one and two dimensions. These models are relevant for potential experimental realizations of polariton Mott insulators based on trapped ions or microwave stripline resonators. We obtain the Mott-superfluid phase boundary and calculate excitation spectra in the Mott phase using numerical and analytical methods. Including the additional hopping terms leads to a larger Mott phase in the case of trapped ions, and to a smaller Mott phase in the case of stripline resonators, compared to the original model with nearest-neighbor hopping only. The critical hopping for the transition changes by up to about 50 percent in one dimension and by up to about 20 percent in two dimensions. In contrast, the excitation spectra remain largely unaffected.

Spatially Modulated Two-Photon Luminescence from Si−Au Core−Shell Nanowires

Si−Au core−shell nanowires were synthesized with a two-step strategy combining chemical vapor deposition and wet chemistry methods. Si core diameter, Au shell thickness, and wire length were controlled during synthesis. Under a far-field two-photon excitation scanning microscope, spatially modulated two-photon luminescence (TPL) was observed from the core−shell nanowires prepared with several micrometers in length. The mode spacing scales linearly with the length of nanowires for samples with 15 and 40 nm Au shells. The spatial modulation pattern was found to be independent of the excitation wavelength. The TPL intensity displayed a cos2 dependence on the excitation field polarization, indicating a sequential two-photon excitation process enhanced by the longitudinal plasmon field. The spatially modulated TPL is interpreted by a standing wave model of surface plasmon polaritons along the core−shell nanowire which acts as a Fabry−Perot resonator. These results suggest TPL imaging of Si−Au core−shell nanowi...

Directly Probing the Anisotropic Optical Emission of Individual ZnO Nanorods

We report on the anisotropic optical emission of individual ZnO nanorods directly measured by angular-resolved photoluminescence imaging and spectroscopy with independent excitation and detection optics. A reduced diameter at the subwavelength scale results in degraded waveguiding efficiency and more divergent emission at the top ends of individual ZnO nanorods grown by chemical vapor deposition. The near-band-edge (NBE) emission from the nanorod ends exhibits strong angular dependence in both emission intensity and spectral line shape. A continuous intensity increase and spectral red shift of the NBE emission have been observed as the detection direction varies from the radial direction to the axial direction. The pronounced red shift (>60 meV) is primarily attributed to the transition from free exciton (FX) emission to its 2LO phonon replica (FX-2LO) emission. Our results support an exciton−polariton model for the waveguiding behavior of ZnO nanorods and demonstrate the dominant role of the FX-2LO exciton−phonon interaction in the waveguiding process. We also show that the excitation angle has little influence on the NBE emission but can greatly modify the deep level emissions.

Hybrid Plasmonic Waveguide Based on Tapered Dielectric Nanoribbon: Excitation and Focusing

The nanofocusing of light source was proposed and simulated using the dielectric-loaded surface plasmon polariton (SPP) model with various laterally tapered planar dielectric architectures on the top surface of the metal. By using finite-difference time-domain method, enhancement factor for the local electric field under distinctive incident polarization was analyzed with different taper apexes under various incident wavelengths and incident angles of the excitation laser. The SPP dispersion and the effect of dissipation on adiabatic nanofocusing of SPP in a sharp taper structure were used to predict the optimal taper angles of the structure and to explain the phenomena of SPP wave slowing down as it propagating toward the taper end. This SPP nanofocusing process was also experimentally realized by illuminating the structure of a tapered CdS nanoribbon deposited on the Ag surface. As the emission of the focused SPP at the taper end, the proposed plasmonic structure can be severed as a light nanosource emitter in the future optical integrated circuits.

Surface plasmon waves generated by nanogrooves through spectral interference

A pure surface plasmon polariton (SPP) model predicted that the SPP excitation in a slit-groove structure at metallodielectric interfaces exhibits an intricate dependence on the groove width P. Lalanne et al. [Phys. Rev. Lett. 95, 263902 (2005); P. Lalanne et al.Nat. Phys. 2, 551 (2006)]. In this paper, we present a simple far-field experiment to test and validate this interesting theoretical prediction. The measurement results clearly demonstrate the predicted functional dependence of the SPP coupling efficiency on groove width, in good agreement with the SPP picture.

Excitation spectra of strongly correlated lattice bosons and polaritons

Spectral properties of the Bose-Hubbard model and a recently proposed coupled-cavity model are studied by means of quantum Monte Carlo simulations in one dimension. Both models exhibit a quantum phase transition from a Mott insulator to a superfluid phase. The dynamic structure factor $S(k,\ensuremath{\omega})$ and the single-particle spectrum $A(k,\ensuremath{\omega})$ are calculated, focusing on the parameter region around the phase transition from the Mott insulator with density one to the superfluid phase, where correlations are important. The strongly interacting nature of the superfluid phase manifests itself in terms of additional gapped modes in the spectra. Comparison is made to recent analytical work on the Bose-Hubbard model. Despite some subtle differences due to the polaritonic particles in the cavity model, the gross features are found to be very similar to the Bose-Hubbard case. For the polariton model, emergent particle-hole symmetry near the Mott lobe tip is demonstrated and temperature and detuning effects are analyzed. A scaling analysis for the generic transition suggests mean-field exponents, in accordance with field-theory results.

Plasmon-polariton surface modes and nanostructuring of semiconductors by femtosecond laser pulses

This paper analyzes the published experimental data on the surface breakdown of semiconductors as a result of the action of a series of pulses of polarized femtosecond laser radiation, accompanied by the formation of regular and disordered micro- and nanostructures. The detected features of the ordered breakdown of transparent and opaque semiconductors and insulators are explained in terms of an extended universal polariton model of laser-induced breakdown of condensed media, including the excitation and interference of cylindrical surface plasmon-polaritons.