Specific features of the spectral properties of a cholesteric liquid crystal with a resonance defective nanocomposite layer

This paper reports on studying the spectral properties of a cholesteric liquid crystal with a defective layer of a nanocomposite consisting of metallic nanoballs dispersed in a transparent matrix and characterized by an effective resonance dielectric permittivity. The transmission, reflection, and absorption spectra of waves of both circular polarizations have been calculated, and the spectral splitting of the defective mode when its frequency coincides with the resonance frequency of the nanocomposite has been studied. An essential dependence of the splitting on the nanoball concentration in the defect has been established. It has been shown that, depending on the position of the resonance frequency with respect to the boundaries of the cholesteric band gap, an additional passband appears in the transmission spectrum, which corresponds to waves of the diffracting circular polarization, or an additional band gap for waves of both circular polarizations, which are substantially modified with variations of both the incidence angle of light and the cholesteric helix pitch.     

Ray splitting in the reflection and refraction of surface acoustic waves in anisotropic solids

This paper examines the conditions for, and provides examples of, ray splitting in the reflection and refraction of surface acoustic waves (SAW) in elastically anisotropic solids at straight obstacles such as edges, surface breaking cracks, and interfaces between different solids. The concern here is not with the partial scattering of an incident SAW's energy into bulk waves, but with the occurrence of more than one SAW ray in the reflected and/or transmitted wave fields, by analogy with birefringence in optics and mode conversion of bulk elastic waves at interfaces. SAW ray splitting is dependent on the SAW slowness curve possessing concave regions, which within the constraint of wave vector conservation parallel to the obstacle allows multiple outgoing SAW modes for certain directions of incidence and orientation of obstacle. The existence of pseudo-SAW for a given surface provides a further channel for ray splitting. This paper discusses some typical material configurations for which SAW ray splitting occurs. An example is provided of mode conversion entailing backward reflection or negative refraction. Experimental demonstration of ray splitting in the reflection of a laser generated SAW in GaAs(111) is provided. The calculation of SAW mode conversion amplitudes lies outside the scope of this paper.     

Traveling of light through a 1D photonic crystal containing a defect layer with resonant dispersion

Spectral properties of a 1D photonic crystal that is comprised of two multilayered dielectric mirrors and a nanocomposite layer between them as a structural defect are studied. The nanocomposite consists of silver nanoballs dispersed in a transparent matrix and is characterized by an effective resonant permittivity. The spectral manifestation of the defect mode splitting for the s-polarized waves is studied as a function of the angle of incidence and concentration of nanoballs. Specific features of the transmission spectra for the s- and p-polarized waves are established for the angle of incidence equal to the Brewster angle of the seeding photonic crystal. It is shown, in particular, that, in the region of the continuous transmission spectrum of the spolarized waves, there arises an additional bandgap caused by mixing of the resonant mode with photonic modes.     

Spectrum of magnetostatic waves in a ferromagnet with a moving superlattice of domain walls

The spectral properties of magnetostatic waves in a ferromagnet with a moving periodic domain structure are considered within the exchange-free magnetostatic approximation. It is demonstrated that the Doppler frequency shift caused by the domain-wall motion leads to the splitting of the spectrum of each magnetostatic wave mode into two dispersion branches, namely, into high-frequency and low-frequency branches. It is established that the larger the mode number, the larger the separation between these branches with respect to the mode spectrum in the presence of the static domain structure.     

Optical properties of nanostructured 2D metal-dielectric photonic crystals with a lattice defect

Optical properties of 2D nanocomposite-based photonic crystals with a lattice defect are studied. The nanocomposite comprises metallic nanospheres dispersed in a transparent matrix and is characterized by an effective resonant permittivity. Transmission spectrum for s-polarized waves at oblique incidence is calculated. Spectral manifestation of the splitting of the defect mode when its frequency coincides with the resonant frequency of the nanocomposite is studied. The essential dependence of the splitting on the angle of incidence and concentration of metallic nanospheres in the nanocomposite matrix is established. Specific features of spatial distribution of the electric field intensity in defect modes of crystals are analyzed.     

Spectral properties of electroacoustic waves in a ferroelectric with a moving periodic domain structure

The propagation of shear waves in a tetragonal ferroelectric with a moving superlattice of 180° domain walls (DW) is considered in a quasistatic approximation. It is found that the spectrum of shear waves consists of alternating allowed and forbidden bands in both cases of static and moving superlattices. It is shown that, due to the Doppler shift in the wave eigenfrequencies, the motion of the DW superlattice causes the degenerate roots of the dispersion equation to split and the splitting increases with the vibration mode number. The acoustic nonreciprocity induced by the moving DW superlattice in the ferroelectric is discussed.     

Interactions of spin waves with a magnetic vortex

We have investigated azimuthal spin-wave modes in magnetic vortex structures using time-resolved Kerr microscopy. Spatially resolved phase and amplitude spectra of ferromagnetic disks with diameters from 5 microm down to 500 nm reveal that the lowest order azimuthal spin-wave mode splits into a doublet as the disk size decreases. We demonstrate that the splitting is due to the coupling between spin waves and the gyrotropic motion of the vortex core.     

Bidirectional oscillations in Er-doped fiber ring cavity with polarization splitting for rotation sensing

The structure of an all-fiber Erbium-doped fiber ring cavity with bidirectional single-mode oscillations and a rotation-sensitive beat signal for gyro applications is reported in this letter. The structure is achieved by introducing a polarization splitting method to filter the bidirectional oscillations and to control the mode coupling of the counter-propagating waves. Two distinct behaviors of the beat signal are identified, namely, the linear mode coupling situation caused by the back-reflection of the optical elements and the nonlinear mode coupling situation attributed to spatially non-uniform saturation in gain medium. Experiments are conducted to show the cavity rotation rate dependence of the beat frequency shift. The results are in good agreement with the theoretical predictions.     

On the interaction of counterrunning radiation in a mirrorless device

The interaction of counterrunning light waves which are coupled via backward Bragg scattering from the self-induced structure in an active medium is investigated. The self-induced coupling of the waves presents a negative feedback and leads to the departure of the waves' frequencies from each other. The departure is limited by the finite width of the gain curve and has an optimum value, which corresponds to the maximum intensity of the waves. The amplification of the counterrunning waves is unstable with respect to the departure of the waves intensities from each other, and the eventual result is the one-directional amplification in a mirrorless device. The frequency splitting of the superradiant spectra is discussed as well.     

Electromagnetically induced transparency in a molecular gas

The dynamic Stark effect on the as Q(5,4) transition of the 0 → 1 vibrational band of the ν₂ mode of ammonia ¹⁵NH₃ was studied by the method of copropagating waves of radiation of two ¹³CO₂ lasers operating at the R(18)_I line. For waves with mutually orthogonal polarizations, which propagated in a waveguide cell, the intensity of the saturating radiation reached 225 W/cm², and the absorption line of the probing radiation had the form of a two-hump curve with a splitting that was consistent with the Rabi frequency for the ammonia transition being investigated. At the maximum intensity of the saturating radiation, complete transparency was observed at the center of the absorption line of ¹⁵NH₃. When identically polarized saturating and probing waves propagating in a cell at a small angle with respect to each other were used, the splitting was more weakly manifested. The effect of a spatial inhomogeneity of the optical fields on the shape of the line of saturated absorption is discussed.     

The influence of a phase transition on the shock wave dynamics in nuclear matter

The propagation of shock waves in nuclear matter undergoing a phase transition is considered in the framework of hydrodynamical approach. It is shown that as a result of phase transition the splitting of the shock wave in two waves occurs in a certain region of energy of the colliding nuclei. Such a splitting may be manifested in energy and angular distributions of the reaction products.     

Propagation and interaction of nonlinear waves in a liquid with gas bubbles

The propagation and interaction of nonlinear solitonlike waves in a liquid with gas bubbles are considered using the Nakoryakov-Pokusaev-Shreiber two-wave equation. It is shown that these waves exist within the “opacity” window for linear waves. The interaction of such waves propagating in opposite directions may lead to their splitting into secondary localized waves.     

一种新型的光子晶体偏振光分束器的设计

基于光波在直波导和复合结构光子晶体中的传播特性,结合平面波展开法和时域有限差分法,提出并讨论了一种新型的超紧凑的光子晶体偏振光分束器. 它是由输入波导,分束结构和输出波导三部分组成. 对这种结构的三角晶格光子晶体光分束器的数值计算与模拟结果表明,该结构可以实现TE模和TM模的高效大角度分离,并且在通信波段设计尺寸小,这些特性使其在未来的集成光回路中有着重要的应用前景. 关键词： 偏振光分束器 能带结构 平面波展开法 时域有限差分法     

Optomechanical dynamics in detuned whispering-gallery modes cavity

The dynamics of a microresonator in detuned whispering-gallery modes (WGM) cavity opto-mechanical system are investigated by the quantum Langevin equation. A WGM cavity coupling to two parallel waveguides is devised to study the transmission and reflection of this system. In single mode WGM cavity, without optomechanical coupling, both the transmission and reflection of the cavity present a Lorentzian dip and peak. When the coupling between the cavity mode and mechanical mode is considered, the transmission and reflection of the optomechanical cavity show “W” and “M” shape mode splitting. Moreover, under the action of a controlling and a probe laser, the output field at the probe frequency presents electromagnetically induced transparency (EIT)-like spectrum in the system. We give the physical origin of EIT-like and the pump-probe response for the WGM shares all the features of the Λ system in atoms. Further, due to backscattering, the two traveling waves in WGM are coupled with a rate γ. The transmission and reflection of the optomechanical cavity display three modes splitting in the spectra with optomechanical coupling between the two cavity modes and the mechanical mode.     

Incredible negative values of effective electromechanical coupling coefficient for surface acoustic waves in piezoelectrics

The extraordinary case of increase in velocity of surface acoustic waves (SAW) caused by electrical shorting of the surface of the superstrong piezoelectric crystal potassium niobate, KNbO3, is numerically found. The explanation of this effect is based on considering SAWs as coupled Rayleigh and Bleustein-Gulyaev modes. A general procedure of approximate decoupling of the modes is suggested for piezoelectric crystals of arbitrary anisotropy. The effect under study takes place when the phase velocity of uncoupled sagittally polarized Rayleigh waves is intermediate between the phase velocities of uncoupled shear-horizontal Bleustein Gulyaev waves at the free and metallized surfaces. In this case, the metallization of the surface by an infinitely thin layer may cause a crossover of the velocity curves of the uncoupled waves. The presence of the mode coupling results in splitting of the curves with transition from one uncoupled branch to the other. This transition is responsible for the increase in SAW velocity, which appears to be greater than its common decrease produced by electrical shorting of the substrate surface.     

Specifics of electromagnetic TE waves splitting and combining under the conditions of frustrated total internal reflection in a thin dielectric layer

The possibility of designing optical beam splitters based on frustrated total internal reflection (FTIR) is considered. A theory describing splitting of a single light wave into two waves and interference of two light waves in a thin dielectric gap under the FTIR conditions is presented. The resulting expressions are analyzed, and the curves describing the behavior of light beams in the process of their splitting and combining in a thin dielectric layer under the FTIR conditions are plotted.     

Quantum processes in a two-mode laser field

The probabilities of the emission of a photon by an electron and e ⁺ e ^?-pair photoproduction in a field which is a superposition of two electromagnetic plane waves with different frequencies and propagating in the same direction are obtained. The case where the frequencies of the two modes are commensurate is studied in detail. This case is interesting primarily because of the existence of effects due to the interference of amplitudes, corresponding to a different number of photons absorbed from different modes but having the same total 4-momentum. It is shown that the optimal field for observing interference effects is a field such that the ratio of the mode frequencies is 3. The probabilities of radiation and pair-photoproduction processes in the field of a monochromatic plane wave and in a two-mode field, obtained by splitting the initial wave into two waves, are compared. It is shown that the total probability of the emission of a photon by an electron in a two-mode field is lower than and the probability of pair photoproduction is higher than the probabilities of the same processes in the initial wave. The increase in the pair-photoproduction probability is explained by the fact that additional channels for reactions which are forbidden in the initial monochromatic field open up in a two-mode field.     

Normal mode splitting and ground state cooling in a Fabry-Perot optical cavity and transmission line resonator

Optomechanical dynamics in two systems which are a transmission line resonator and Fabrya-Perot optical cavity via radiation-pressure are investigated by linearized quantum Langevin equation. We work in the resolved sideband regime where the oscillator resonance frequency exceeds the cavity linewidth. Normal mode splittings of the mechanical resonator as a pure result of the coupling interaction in the two optomechanical systems is studied, and we make a comparison of normal mode splitting of mechanical resonator between the two systems. In the optical cavity, the normal mode splitting of the movable mirror approaches the latest experiment very well. In addition, an approximation scheme is introduced to demonstrate the ground state cooling, and we make a comparison of cooling between the two systems dominated by two key factors, which are the initial bath temperature and the mechanical quality factor. Since both the normal mode splitting and cooling require working in the resolved sideband regime, whether the normal mode splitting influences the cooling of the mirror is considered. Considering the size of the mechanical resonator and precooling the system, the mechanical resonator in the transmission line resonator system is easier to achieve the ground state cooling than in optical cavity.     

Optical data transfer by switching waves in bistable interferometers with a specified optical thickness distribution

The evolution of switching wave fronts in thin-layer bistable Fabry-Perot interferometers with a specified topology of the transverse distribution of the optical thickness of an intermediate layer is studied. The conditions of passage of switching waves through the boundary between regions with different thicknesses and of tunneling of waves through a barrier of a variable thickness and width formed by two such boundaries are determined by numerical modeling. The possibilities of the formation of planar waveguide channels, regions of retardation and acceleration of the motion of switching waves, and points of the splitting and joining of their fronts are demonstrated, as well as the possibility of creating planar structures on this basis that can perform optical logic operations.     

Microscopic theory of dipole-exchange spin waves in magnetic multilayers

A microscopic model is employed to calculate the spectrum of dipole-exchange spin waves in multilayers in which thin ferromagnetic films are separated by non-magnetic spacers. Two configurations are considered: in one the films have magnetizations parallel to each other, in the other the magnetizations are antiparallel. The calculations extend a previous microscopic formalism that allows the calculation of the dipole-exchange spin wave spectrum in thin films. The results show the splitting of the frequency bands and the mode mixing caused by the dipolar interaction between the films as a function of spacer thickness.Received: 26 May 2004, Published online: 12 August 2004PACS: 75.30.Ds Spin waves - 75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.) - 75.70.-i Magnetic properties of thin films, surfaces, and interfaces