Surface plasmon polariton contributions to strokes emission from molecular monolayers on periodic Ag surfaces

Surface enhanced Raman scattering from molecular monolayers adsorbed on a holographic grating and covered by Ag has been studied. The coupling of surface plasmon polaritons to light through the grating produces emission similar to the continuum observed in other surface Raman experiments. The angular dependence of the surface Raman scattering shows that enhanced Raman cross-sections can arise from scattering of surface plasmon polaritons into light by the localized molecular vibrations.     

Angular Dependences of the Intensity of the Raman Light Scattering on Polaritons in a Gallium Phosphide Crystal

Optics and Spectroscopy - Raman light scattering on phonons and polaritons is measured in a gallium phosphide sample. An unfocused beam of a 532-nm single-mode laser was used for excitation. A...     

Light scattering by extraordinarily polarized polaritons

The objective of this work is to investigate how the anisotropy of the interaction between dipole-active vibrations of a crystal lattice and infrared electromagnetic waves is manifested in the spontaneous parametric light scattering spectra of polaritons (Raman scattering by small angles). The case where scattering occurs by extraordinarily polarized polaritons—quasiparticles formed as a result of the coupling of the wave polarized in the symmetry plane of a biaxial crystal simultaneously with two phonons possessing orthogonal dipolar moments—is studied. A series of spectra of equilibrium fluctuations of the electromagnetic (infrared) field, each of which represents an intensity distribution in frequency-wave number coordinates for a fixed direction of the wave vector, are constructed on the basis of a scattering model that takes account of the tensor character of the permittivity and the quadratic and cubic susceptibilities of the crystal. Analysis of the computed spectra identified the basic laws and dependences which are determined by the anisotropy of the electromagnetic susceptibilities of various orders and made it possible to explain previous experimental results which cannot be interpreted on the basis of the generally accepted model of transversely polarized polaritons. A method is proposed for determining the contributions of the dipole-active vibrations of the crystal lattice to the permittivity and the quadratic and cubic susceptibilities, as well as the absorption of the material from the spectra of the extraordinarily polarized polaritons.     

Anomalous light scattering on polaritons in the region of phase transition in α-LiJO3 single-crystals

The experimental investigation of the temperature dependence of spectra of spontaneous Raman light scattering on polaritons in α-LiJO₃ crystal has been carried out. An anomalous broadening of the frequency-angular spectrum of scattered radiation was found in the region of phase transition α→γ→β at 256°C. It is assumed that this phenomenon is due to an anomalous increase of non-linearity of the third order and, hence, of the probability of the four-particle scattering process at which a pumping photon is decayed into a photon and two polaritons during a common act.     

Why metallic surfaces with grooves a few nanometers deep and wide may strongly absorb visible light

It is theoretically shown that nanometric silver lamellar gratings present very strong visible light absorption inside the grooves, leading to electric field enhancement of several orders of magnitude. It is due to the excitation of quasistatic surface plasmon polaritons with particular small penetration depth in the metal. This may explain the abnormal optical absorption observed a long time ago on almost flat Ag films. Surface enhanced Raman scattering in rough metallic films could also be due to the excitation of such quasistatic plasmon polaritons in grain boundaries or notches of the films.     

Relaxation processes at high excitation levels and Bose-Einstein condensation of excitons in ZnTe crystals

The singularities of low-temperature emission spectra obtained for ZnTe crystals excited resonantly by a strongly monochromatic source are investigated. The possibility of attaining the coherent luminescent emission due to the exciton-exciton interaction under these conditions is proved. The appearance of the non-polarized needle-like peak and the processes of inelastic interaction of polaritons of the upper polariton branch (UPB) as well as the disappearance of the Raman component are interpreted as the spectral attributes of Bose-Einstein condensation of UPB polaritons.     

Resonant Raman scattering and luminescence of excitonic polaritons

Resonant light scattering spectra of excitonic polaritons are calculated with a model system consisting of one exciton band and LO and LA phonons by solving a balance equation describing the kinetic energy relaxation of polariton. The relative intensity of Raman sattering and luminescence changes with varying the incident photon energy because of the competition among various decay mechanisms of polariton. The results are in qualitative agreement with recent experimental observations.     

Resonant Raman Scattering by excitonic polaritons in semiconductors

We report results on Resonant Raman Scattering (RRS) mediated by excitonic polaritons in a high-purity semiconductor (CdTe) at low temperatures. For the first time ingoing and outgoing resonances at the n = 1, 2, 3 exciton states are detected on the one and two LO-phonon RRS. The transformation at resonance of sharp Raman peaks into well-thermalized exciton luminescence bands is observed for every ingoing, outgoing or intermediate state resonance.     

Dispersion of Exciton Polaritons in Terbium Nitrate Hexahydrate

The dispersion relations of exciton polariton waves in terbium nitrate hexahydrate are determined based on the model of the interaction of electromagnetic waves with resonant electronic states of Tb³⁺ ions at the ⁵D₄–⁷F₆ transition. Frequencies of unitary polaritons characterized by refractive indices equal to unity are determined. It is shown that the group velocity of electromagnetic waves in the region of unitary polaritons is lower than the speed of light in vacuum by several orders of magnitude. A sharp increase in the efficiency of photoluminescence and Raman scattering is predicted in the case where the excitation radiation frequency approaches the unitary polaritons frequency.     

Observation of increase in Raman intensity of surface phonon polaritons on rough surfaces of ZnTe

An increase in Raman intensity of surface phonon polaritons has been observed in free-standing thin slabs (thickness ～ 7 μm) of single- crystal ZnTe with rough surfaces by a conventional Raman-scattering technique at room temperature. The samples with various root-mean- square roughness heights have been prepared by making use of final polishing powders with different mean-grit sizes, and the surface roughness has been confirmed by measuring the intensities of the diffuse scattering of the laser light. The increase of the Raman intensity is proportional to the mean-square height of the surface roughness, and the shift of the dispersion relation is also proportional to it. The frequency shift is explained by a perturbation theory of the surface-roughness-induced scattering.     

Dynamic amplification and generation of entangled polaritons in doped media

We have developed a theory that describes the formation of probe-field polaritons under the conditions of strong coupling in the Raman ??-scheme interaction in a Y₂SiO₅ crystal doped with ⁵⁹Pr atoms. The threshold optical pump power for efficient amplification of the probe-field polaritons in a medium consisting of three-level atoms is determined. The onset of strong nonclassical correlations (entanglement) between the light- and dark-state polaritons at the near-threshold pump power is established.     

Bose-Einstein condensation of stationary-light polaritons

We propose and analyze a mechanism for Bose-Einstein condensation of stationary dark-state polaritons. Dark-state polaritons (DSPs) are formed in the interaction of light with laser-driven 3-level Lambda-type atoms and are the basis of phenomena such as electromagnetically induced transparency, ultraslow, and stored light. They have long intrinsic lifetimes and in a stationary setup, a 3D quadratic dispersion profile with variable effective mass. Since DSPs are bosons, they can undergo a Bose-Einstein condensation at a critical temperature which can be many orders of magnitude larger than that of atoms. We show that thermalization of polaritons can occur via elastic collisions mediated by a resonantly enhanced optical Kerr nonlinearity on a time scale short compared to the decay time. Finally, condensation can be observed by turning stationary into propagating polaritons and monitoring the emitted light.     

Raman scattering by hot and thermal polaritons in crystal quartz

Summary Nonlinear mixing of IR and visible radiation,i.e. coherent Raman scattering by polaritons driven by a CO₂ laser, has been used to obtain the dispersion curve and its width inq-space of the polariton associated to theE-phonon at 1065 cm⁻¹ in crystal quartz. It is shown in this paper that a direct method to determine indipendently, with high precision, the refractive index and absorbance of a crystal can be obtained in this way. The results are compared with accurate data obtained from Raman scattering by polaritions in thermal equilibrium and very good agreement is found between the two measurements. It is finally shown that nonlinear-mixing techniques turn out to be completely consistent with the simple picture of scattering of light by hot polaritons. This work was supported by the Italian Consiglio Nazionale delle Ricerche del Ministero della Pubblica Istruzione.     

Back-propagating surface polaritons of a one-dimensional photonic crystal containing single negative metamaterials

The existence of the surface polaritons at the interface separating a semi-infinite uniform left-handed metamaterial and a one-dimensional photonic crystal composed of alternating layers of two kinds of single-negative materials is theoretically investigated. The dispersion characteristics of the surface polaritons are analyzed and demonstrated that in the presence of metamaterial, the surface polaritons are sensitive to light polarization, so that there exist only backward TM-polarized (or TE-polarized) kind of the surface polaritons depending on the ratio of the thicknesses of the two periodic stacking layers. The existence regions of the surface polariton modes are determined for both TM-polarized and TE-polarized surface polariton modes.     

Temperature-dependent polarization of resonance Raman scattering in CdS

Temperature-dependent polarization of the 4658 Å—3LO Raman line was studied together with that of the 4727 Å—2LO Raman line in resonance Raman scattering (RRS) in CdS. Temperature-dependent polarization is strongly related to the A-exciton in CdS as a resonant intermediate state. Experimental results are well understood when RRS around the A-exciton is considered as the inelastic scattering of exciton—polaritons by LO phonons.     

Subwavelength propagation and localization of light using surface plasmons: A brief perspective

Surface plasmons at the metal–dielectric interface have emerged as an important candidate to propagate and localize light at subwavelength scales. By tailoring the geometry and arrangement of metallic nanoarchitectures, propagating and localized surface plasmons can be obtained. In this brief perspective, we discuss: (1) how surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) can be optically excited in metallic nanoarchitectures by employing a variety of optical microscopy methods; (2) how SPPs and LSPs in plasmonic nanowires can be utilized for subwavelength polarization optics and single-molecule surface-enhanced Raman scattering (SERS) on a photonic chip; and (3) how individual plasmonic nanowire can be optically manipulated using optical trapping methods.     

半导体微腔中腔模、重空穴激子模和轻空穴激子模耦合

采用传输矩阵方法利用半经典的线性色散模型,计算半导体微腔内同时存在重空穴激子、轻空穴激子时,在不同入射角度下的反射谱,同时,利用三简谐振子耦合模型计算了在不同入射角度下,腔模同时和重空穴激子模、轻空穴激子模耦合所形成的三支腔极化激元的能量,以及腔模、重空穴激子模、轻空穴激子模分别在三支腔极化激元中所占的权重,结果表明随着入射角的增加腔极化激元的高能支和两个低能支之间存在明显的反交叉现象,同时,腔模和重空穴激子模、轻空穴激子模在腔极化激元中所占的权重呈现增加或减小的趋势 关键词： 半导体微腔 腔极化激元 激子     

Theoretical Treatment of Nonstationary Scattering by Phonons and Polaritons Part II. Transient Raman Scattering by Polaritons and Dipole Active Phonons

The stimulated Raman scattering by polaritons and phonons generated by the fluctuations of the crystal vibrations is investigated for the transient regime. The transient gain and the scattering energy is given for the case of retarded or advanced Stokes and polariton pulses in relation to the laser pulse. Moreover, the influence of phase modulation of the laser pulse on the transient SRS by polaritons is discussed.     

Generation of terahertz radiation in cubic non-centrosymmetric crystals

The conditions of parametric radiation generation on polaritons in cubic noncentrosymmetric crystals are studied. The possibility of such generation is theoretically justified. The polariton radiation frequencies are calculated for GaP, ZnSe, ZnTe, and GaAs crystals. The obtained generation frequencies are compared to the experimental results on Raman scattering on polaritons. The block diagram of the terahertz radiation generator operation using a GaP crystal and a pulsed laser with high peak power at low energy of laser pump pulses is presented. The lasing frequency shift is analyzed depending on the scattering geometry. The coefficient of exciting radiation conversion to the terahertz range is determined.     

Quantum theory of the polariton of the bounded semiconductor

The quantization of the polariton field is carried out for the semiconductor bounded by the surface. The orthonormalized set of the normal mode of the vacuum-semiconductor system is explicitly given for the case of the excitonic polarization field with the standard form of the spatial dispersion and the additional boundary condition of the elastic type. The scheme is employed to interpret the several experiments: optical reflectance and transmission, resonant Raman and Brillouin scattering, and the induced absorption of the polariton. Particularly, a recent experiment on CuCl which shows the existence of correlation among the polaritons and reflected light is discussed in view of the quantum picture.