Dispersion Law Of Waves Research Articles

Experimental investigation on three-dimensional structures of wind wave surfaces

This study experimentally investigated the three-dimensional features of wind wave surfaces in a laboratory. Free surfaces of wind waves under five types of wind velocities at four wind fetches were reconstructed by a stereo camera system. The dispersion law of wind waves was obtained from the spatio–temporal spectrum and showed a Doppler shift owing to the drift current. The wavenumber spectrum in the crosswind and wind direction follow the same power law of k−3 in the equilibrium range. Dynamic mode decomposition (DMD) was used to investigate the three-dimensional structures of the wave surface. Two different modes—the parallel mode and the net mode—were defined to characterize the structure of the wave surface. The parallel mode represents the average wave behavior over time, whereas the net mode represents the three-dimensional characteristics of the wind waves. The ratio of the wave number in the crosswind to the wind direction decreases with increasing wind fetch and converges to approximately 0.5. The wind wave spectrum in the wavenumber space had an elliptical distribution. Using the dispersion law, the wind wave spectrum in the (ω,k) domain can be predicted by a quartic surface.

Emission of conical THz radiation induced by bichromatic pumpXwaves in an air plasma

The $X$-wave formation during the propagation of bichromatic femtosecond laser pulses in an air plasma filament and THz radiation generation has been investigated both experimentally and theoretically. We found that in this case the pump waves as well as THz radiation propagate as $X$ waves at the same group velocity. Therefore, the cone angle of generated THz radiation could be estimated using the $X$-wave dispersion law. Hence, the proposed model allows an alternative characterization of generated THz radiation based on the frequency-angular spectra of pump waves registered after propagation in the created plasma filament.

Поверхностные электромагнитные волны Дьяконова на границе раздела анизотропных двуосных кристаллов

A general approach to analysis of Dyakonov surface waves at the interfaces of anisotropic biaxial crystals is proposed, taking into account arbitrary spatial orientation of the media tensors principal axes. This approach is based on the operator representation of macroscopic Maxwell equations corresponding to the quantum-mechanical equations for photon states in an inhomogeneous anisotropic media. Surface wave dispersion law is investigated in the most general case. It is established that the interface eigenmode dispersion is closely related to the dispersion of bulk waves in the partnering media, which is a specific feature of Dyakonov waves. The electromagnetic field spatial distribution is investigated in the direction orthogonal to the boundary plane. The surface wave angular existence domain is determined. It’s dependencies on the rotation angles of the media optical axes are studied as well.

Dyakonov Surface Waves at the Boundary of Anisotropic Biaxial Crystals

A general approach to analysis of Dyakonov surface waves at the interfaces of anisotropic biaxial crystals is proposed, taking into account arbitrary spatial orientation of the media tensors principal axes. This approach is based on the operator representation of macroscopic Maxwell equations corresponding to the quantum-mechanical equations for photon states in an inhomogeneous anisotropic media. Surface wave dispersion law is investigated in the most general case. It is established that the interface eigenmode dispersion is closely related to the dispersion of bulk waves in the partnering media, which is a specific feature of Dyakonov waves. The electromagnetic field spatial distribution is investigated in the direction orthogonal to the boundary plane. The surface wave angular existence domain is determined. It's dependencies on the rotation angles of the media optical axes are studied as well. Keywords: electromagnetic surface waves, interface photon states, anisotropic media, biaxial materials.

Dzyaloshinskii–Moriya interaction determined from spin wave nonreciprocity and magnetic bubble asymmetry in Pt/Co/Ir/Co/Pt synthetic ferrimagnets

We present analysis of the effect of Dzyaloshinskii–Moriya interaction (DMI) on spin wave nonreciprocity and bubble expansion asymmetry in Pt/Co/Ir/Co/Pt synthetic ferrimagnets with perpendicular magnetic anisotropy. We propose analysis of the DMI by Brillouin light scattering technique (BLS) and Kerr microscopy (MOKE) in the presence of interlayer exchange coupling strongly changing spin wave dispersion law and field dependences of domain wall velocity in comparison with those observed earlier in Ir/Co/Pt structures with a single Co layer. We have determined DMI values of each Co layer from unusually inverted dependence of velocity of the domain wall on in-plane magnetic field. Opposite signs of effective fields and DMI fields in the two Co layers invert field dependence of the domain wall velocity. DMI energy determined from BLS is higher than values, determined by bubble expansion.

Resonant four-photon scattering of collinear laser pulses in plasma.

Exact four-photon resonance of collinear planar laser pulses is known to be prohibited by the classical dispersion law of electromagnetic waves in plasma. We show here that the renormalization produced by an arbitrarily small relativistic electron nonlinearity removes this prohibition. The laser frequency shifts in collinear resonant four-photon scattering increase with laser intensities. For laser pulses of frequencies much greater than the electron plasma frequency, the shifts can also be much greater than the plasma frequency and even nearly double the input laser frequency at still small relativistic electron nonlinearities. This may enable broad range tunable lasers of very high frequencies and powers. Since the four-photon scattering does not rely on the Langmuir wave, which is very sensitive to plasma homogeneity, such lasers would also be able to operate at much larger plasma inhomogeneities than lasers based on stimulated Raman scattering in plasma.

Dispersion Laws, Nonlinear Solitary Waves, and Modeling of Kernels of Integro-Differential Equations Describing Perturbations in Hydrodynamic-Type Media With Strong Spatial Dispersion

An integro-differential equation simulating a medium with strong spatial dispersion and hydrodynamic-type nonlinearities (the Whitham equation) is considered. A method is proposed for constructing the kernel of the integral term that makes it possible to qualitatively take into account the specifics of the dispersion laws of linear waves in media with spatial dispersion. The case where the kernel contains two independent parameters characterizing its amplitude and width is considered in detail. The dispersion laws of linear waves, as well as solutions in the form of solitary waves with limiting and small amplitudes, are obtained and analyzed. In particular, it is shown that the appropriate choice of parameters makes it possible to obtain the value of the tapering angle at the peak of a solitary wave with limiting amplitude on the surface of a fluid layer; this value is equal to the Stokes angle.

Hamiltonian formalism for nonlinear spin wave dynamics under antisymmetric interactions: Application to Dzyaloshinskii-Moriya interaction

A Hamiltonian formalism is applied for the investigation of nonlinear spin wave dynamics under the influence of antisymmetric magnetic interactions. In the framework of this formalism we account not only for symmetric magnetic interactions (exchange, dipole-dipole, magnetocrystalline anisotropy), but also for antisymmetric interactions, such as Dzyaloshinskii-Moriya exchange interaction. The account of antisymmetric exchange, in general, could lead to the appearance of an additive nonreciprocal term in the spin wave dispersion law. We present the generalization of the linear transformation for the diagonalization of quadratic part of the Hamiltonian (so-called ``third Holstein-Primakoff transformation'') for the antisymmetric case, which allowed us to obtain generalized expressions for the coefficients of the nonlinear three- and four-magnon interactions. As an example, nonlinear spin wave interactions in ultrathin ferromagnetic nanowires and films subjected to interfacial Dzyaloshinskii-Moriya interaction (IDMI) are considered. It was found that three-magnon interaction coefficients in the ``Damon-Eshbach'' geometry are nonzero only in the case of the noncollinear interacting spin waves, and vanish in the case of the collinear spin waves. It was also found that the nonlinear spin wave frequency shift caused by the four-magnon interaction is nonreciprocal, and has the sign opposite to that of the nonreciprocal term in linear spin wave dispersion, so that the IDMI-induced nonreciprocity of the spin wave spectrum decreases with the increase of the spin wave amplitude.

Магнитозвуковые волны в двумерной электронной ферми-жидкости

The properties of highly viscous fluids at high frequencies become similar to the properties of amorphous solids. In particular, it becomes possible to propagate not only longitudinal sound waves (plasmons for the case of an electron fluid), but also transverse sound waves associated with shear deformations. In this work, transverse sound waves at high frequencies in a twodimensional electron liquid in a magnetic field are studied. The consideration was carried out in the framework of the Landau Fermi-liquid model. It is shown that for a sufficiently large interaction between quasiparticles, the dynamics of excitations of a Fermi liquid is described by the equations of hydrodynamics. The Navier-Stokes equation and expressions for high-frequency shear viscosity coefficients are derived. Based on the equations obtained, the dispersion laws are calculated for transverse and longitudinal magnetosonic waves. It is shown that the cyclotron frequency, which enters in the viscosity coefficients and the dispersion law of transverse magnetosonic waves, is renormalized and typically becomes less than the usual cyclotron frequency, which determines the cyclotron resonance. The latter fact was apparently observed in the photoresistance of highly mobile GaAs quantum wells, in which two-dimensional electrons form a viscous fluid.

Modified dispersion law for spin waves coupled to a superconductor

In this work, we consider dispersion laws of spin waves that propagate in a ferromagnet/superconductor bilayer, specifically in a ferromagnetic film coupled inductively to a superconductor. The coupling is viewed as an interaction of a spin wave in a ferromagnetic film with its mirrored image generated by the superconductor. We show that, in general, the coupling enhances substantially the phase velocity of magnons in in-plane spin wave geometries. In addition, a heavy nonreciprocity of the dispersion law is observed in the magnetostatic surface spin wave geometry where the phase velocity depends on the direction of the wave propagation.

Large-Scale Compressibility in Rotating Flows of Astrophysical Plasma in the Shallow Water Approximation

Two systems of magnetohydrodynamic equations in the shallow water approximation are proposed as a basis for studies in the field of plasma astrophysics: the system of equations with a full allowance for the Coriolis force and the system of equations on the β-plane in which the changes of the Coriolis parameter are linear in coordinate. Both systems of equations take into account such fundamentally important phenomena in plasma astrophysics as the compressibility and external magnetic field effects, increasing significantly the potential for applying these equations to study astrophysical objects. Compressibility in plasma astrophysics is shown to change significantly the dispersion laws for magneto-Poincare, magnetostrophic, and magneto-Rossby waves. The same nonlinear interactions as those in the absence of compressibility have been found to be realized in the case of a compressible rotating plasma. Three-wave equations in the weak nonlinearity approximation, in which the interaction coefficients depend on plasma large-scale compressibility and thermodynamic characteristics, have been derived by the method of multiscale expansions. Expressions for the growth rates of the parametric instabilities of three-wave interactions with large-scale compressibility have been derived.

Magnetoelastic Waves in Ferromagnets in the Vicinity of Lattice Structural Phase Transitions

The dispersion laws for coupled magnetoelastic waves in ferromagnets with uniaxial or cubic symmetry have been calculated. The features of obtained dispersion laws in the vicinity of spin-reorientation phase transitions are analyzed. The interaction between elastic and spin waves is shown to depend on the direction of the ferromagnet magnetic moment. The influence of the magnetoelastic interaction on the dispersion law of quasispin waves in the degenerate ground state of a uniaxial “easy plane” ferromagnet is studied. The results of calculations show that the magnetoelastic interaction eliminates the degeneration and leads to the appearance of a magnetoacoustic gap in the ferromagnet spectrum. The behavior of the spectra of coupled magnetoelastic waves in the vicinity of lattice phase transitions, namely, in the vicinity of martensitic phase transformations in materials with the shape memory effect, is analyzed. The obtained results are used to interpret experimental data obtained for the Ni–Mn–Ga alloy. The phenomenon of a drastic decrease of the elastic moduli for this alloy, when approaching the martensitic phase transition point is explained theoretically. It is shown that the inhomogeneous magnetostriction is the main factor affecting the elastic characteristics of the material concerned. A model dissipative function describing the relaxation processes associated with a damping of coupled magnetoelastic waves in ferromagnets with cubic or uniaxial symmetry is developed. It takes the symmetry of a ferromagnet into account and describes both the exchange and relativistic interactions in the crystal.

High-Frequency Quasi-Potential Waves in the Plasma Formed under Tunnel Ionization of Atoms

The dispersion law and collisionless damping rate of quasi-potential waves in the plasma formed upon tunnel ionization of gas atoms in the field of a short pulse of circularly or linearly polarized radiation are found. It is shown how the frequency and damping rate of quasi-potential waves depend on the wave propagation direction relative to the symmetry axis of the photoelectron distribution. It is established that, in plasma with a toroidal photoelectron velocity distribution, weakly damped waves with a linear dispersion law and frequency above the electron plasma frequency can propagate in a wide range of angles. In the case of a bi-Maxwellian photoelectron distribution, the frequency of weakly damped waves is comparable with the electron plasma frequency and the anisotropy of electron motion manifests itself in relatively small corrections to the dispersion law.

Photoluminescence and polariton dispersion law in terbium nitrate hydrate crystals

The article examines the dispersion law of polariton waves in terbium nitrate hydrate crystals. We have calculated the values of the unitary polaritons frequencies corresponding to the refractive index equal to unit as well as the velocity and the effective mass of the unitary polaritons. The diagram of terms splitting in the low symmetric crystalline field is constructed. It is shown that the abnormal decrease of the polariton waves’ group velocity occurs due to the splitting of the terbium ions spectral terms in the crystalline field. We consider the conditions for the essential increase of the photoluminescence intensity and decrease of the lasing threshold in terbium nitrate hydrate crystals.

Electron modes of plasma generated at tunnel ionization of atoms by a circularly polarized radiation

The collective modes of photoionized plasmas are studied using the model description of electron velocity distribution formed at tunnel ionization of atoms by circularly polarized radiation. The dispersion laws of transverse and approximately longitudinal high-frequency waves propagating at an arbitrary angle to the anisotropy axis of photoelectron distribution are obtained. The dispersion law of potential surface waves is derived. It is shown that the frequency of these waves may be greater than plasma frequency. The aperiodic instability of photoionized plasmas is described.

Interaction between a surface acoustic wave and adsorbed atoms

Within nonlocal elastic interaction between an adsorbed atom and matrix atoms and in consideration of the mirror image forces, a dispersion law of elastic surface acoustic waves is found to the long-wavelength approximation depending on the concentration of adsorbed atoms and the deformation potential of the adatom. The energy width of the surface acoustic mode is calculated depending on the concentration of adsorbed atoms.

Crystallographic features of magnetostatic waves spectra in ferrite films

Influence of crystallographic magnetic anisotropy on dispersion laws of magnetostatic spin waves is discussed. Classification of waves spectra in single crystal films of ferrites is given. The scale of magnetic anisotropy influence on spectra of volume and surface types of waves is investigated. The film model with cubic magnetic anisotropy is constructed and expressions for components of a tensor of the effective demagnetization anisotropy factors are deduced. Results of spectra calculation of magnetostatic waves in a film of yttrium iron garnet are given.

On the dispersion law of neutrons in accelerated matter

In recent experiments with ultracold neutrons, a change in the energy occurring when neutrons pass through an accelerated reflecting sample was detected. The results are in good agreement with theoretical predictions obtained under the assumption that the dispersion law of neutron waves in accelerated matter is the same as that in a sample at rest. Some reasons that this assumption is valid only when the acceleration is below a certain critical value have been presented. A possible experimental test of these reasons has been discussed.

Damping of Sound Waves in Strong Centrifugal Field

A method for numerical calculation of the sound wave damping and dispersion law in a strong centrifugal field of the order of 106 g is considered. The damping is defined from the width of the resonance peak for different wave vectors. In the strong centrifugal field damping of the sound waves essentially exceeds the damping in the quiescent gas.

Quantum field theory based on birefringent modified Maxwell theory

In the current paper the properties of a birefringent Lorentz-violating extension of quantum electrodynamics is considered. The theory results from coupling modified Maxwell theory, which is a CPT-even Lorentz-violating extension of the photon sector, to a Dirac theory of standard spin-1/2 particles. It is then restricted to a special birefringent case with one nonzero Lorentz-violating coefficient. The modified dispersion laws of electromagnetic waves are obtained plus their phase and group velocities are considered. After deriving the photon propagator and the polarization vectors for a special momentum configuration we prove both unitarity at tree-level and microcausality for the quantum field theory based on this Lorentz-violating modification. These analytical proofs are done for a spatial momentum with two vanishing components and the proof of unitarity is supported by numerical investigations in case all components are nonvanishing. The upshot is that the theory is well-behaved within the framework of our assumptions where there is a possible issue for negative Lorentz-violating coefficients. The paper shall provide a basis for the future analysis of alternative birefringent quantum field theories.