Self-and cross-phase modulation accompanying third-harmonic generation in a hollow waveguide

The influence of self-and cross-phase modulation on third-harmonic generation in a hollow waveguide is investigated. Analytic solutions of the coupled equations for the slowly varying amplitudes of the pump pulse and the third harmonic in a gas-filled hollow waveguide are obtained with consideration of self-and cross-phase modulation and first-order dispersion effects. The possibility of controlling the nonlinear phase trajectory of the third harmonic by cross-phase modulation is demonstrated. Zh. éksp. Teor. Fiz. 115, 1561–1579 (May 1999)     

Induced modulation instability of spin waves in ferromagnetic films

Induced modulation instability of backward volume spin waves in ferromagnetic films is investigated. It is found that the nonlinearity of the spin system of a ferromagnetic sample can greatly enrich the spectrum by excitation of spin waves at close frequencies and, in consequence, result in the appearance of a sequence of soliton-like pulses. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 828–832 (10 December 1998)     

Wavelength Converter Using Semiconductor Optical Amplifier Mach-Zehnder Interferometer Based on XPM at 40 Gb/s for Future Transport Networks

Abstract

We have simulated, for the first time, wavelength converter for future broadcast networks at 40 Gb/s using low-cost semiconductor optical amplifiers. The performance analysis is carried out for an all-optical frequency converter based on cross-phase modulation in two semiconductor optical amplifiers arranged in a Mach-Zehnder interferometer configuration to evaluate the efficiency of conversion. The results, evaluated analytically for input, return to zero signal at a bit rate of 40 Gb/s show that conversion is possible over a wavelength separation of 1 nm between the pump and the input wavelength. Increasing the driving current can decrease the cross-phase modulation effect. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths.     

Generation of multicolor vector Kerr solitons by cross-phase modulation, four-wave mixing, and stimulated Raman scattering

We numerically and experimentally show the existence of multicolor vector spatial solitons in a Kerr planar waveguide through the combined effects of cross-phase modulation, four-wave mixing, and stimulated Raman scattering. Mutual spatial guiding of the Raman-Stokes, anti-Stokes, and pump waves is achieved in the high-conversion regime mainly by cross-phase modulation and phase-matched four-wave mixing induced by a power imbalance between Stokes and anti-Stokes components, leading to the generation of a clear-cut sech-shape three-frequency spatial soliton.     

Influence of the cross-phase modulation effect on the polarization states of waves transmitted through a non-linear Fabry–Pe´rot cavity

An analysis of the influence of the cross-phase modulation effect on the polarization states of waves transmitted through a non-linear Fabry–Pe′rot resonator with a self- focusing and self-defocusing Kerr medium is presented. The case is considered of two plane waves with different wavelengths incident on a non-linear Fabry–Pe′rot cavity. It is shown that the polarization states of the transmitted waves change bistably or multistably and depend on the parameters of incident waves and the resonator. This revised version was published online in November 2006 with corrections to the Cover Date.     

Ultrasound in spin glasses II

General expressions are derived for the change of the sound velocity Δv(ω,T) and the damping of sound waves γ(ω,T) in spin glasses for all temperatures and without assuming a specific spin dynamics. The calculation is based on the modulation of the exchange interactions by the sound waves. Explicit results are obtained for diffusive or relaxing spin excitations.     

Transverse spin dynamics of a spin-polarized Fermi liquid

A microscopic derivation of the equations of transverse spin dynamics of a spin-polarized Fermi liquid at zero temperature is given in the leading-order approximation in the frequencies and wave vectors characterizing the spin motion. The equations are applicable for arbitrary degree of polarization and arbitrary deviations of the spin direction from the equilibrium orientation. The solutions describing a coherently precessing two-domain structure and spin waves are examined. In contrast to the assertion discussed in the literature that spin waves are damped at zero temperature, spin waves are found to be undamped in the long-wavelength limit. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 9, 717–721 (10 May 1997)     

Scattering of spin waves by a rectilinear edge dislocation

The propagation of volume spin waves in an unbounded easy-axis magnet containing a rectilinear edge dislocation is studied theoretically. The spin-wave scattering amplitudes are calculated in the Born approximation. It is shown that the spin-wave scattering amplitude vanishes for certain values of the scattering angle. The dependence of the scattering angle on the angle of incidence of the spin waves is found for this case. The transport scattering cross section of spin waves is found. Fiz. Tverd. Tela (St. Petersburg) 40, 2056–2058 (November 1998)     

Analytical description of cross-phase modulation in dispersive optical fibers

The effect of intensity distortion induced by cross-phase modulation in dispersive optical fibers is studied. It is shown that, in most configurations in which distortions that are due to cross-phase modulation can become significant to optical communications, the effect of cross-phase modulation can be described with excellent accuracy by simple analytical expressions. The presented analysis also suggests that intensity distortions owing to cross-phase modulation can be efficiently reduced by linear dispersion compensation.     

Intrapulse depolarization in optical fibers: a classical analog of spin decoherence

We show that the combination of cross-phase modulation and polarization-mode dispersion inside optical fibers leads to a novel phenomenon of intrapulse depolarization manifested as different random states of polarization across the pulse profile. Such polarization evolution of optical pulses is directly analogous to the phenomenon of spin decoherence in semiconductors or pseudospin relaxation in atoms.     

A model for strongly coupled spin waves

The connection between a model of coupled oscillators and the system of coupled spin waves is discussed. Also the region ofk-space is estimated in which the spin-wave amplitudes have appreciable magnitude when a normal mode of coupled spin waves is excited.     

Parametric excitation of spin waves in uniaxial ferrites

Parametric excitation of spin waves in uniaxial ferrites with large anisotropy is investigated theoretically. First-order processes in a sphere with arbitrary orientation of an external static magnetic field, in which case the pumping is oblique, are studied. The threshold field and the parameters of the excited spin waves are calculated numerically for two ferrites — easy-axis and easy-plane. Zh. Tekh. Fiz. 68, 65–71 (May 1998)     

Modulational instability of bright solitary waves in incoherently coupled nonlinear Schrödinger equations

We present a detailed analysis of the modulational instability (MI) of ground-state bright solitary solutions of two incoherently coupled nonlinear Schr?dinger equations. Varying the relative strength of cross-phase and self-phase effects we show the existence and origin of four branches of MI of the two-wave solitary solutions. We give a physical interpretation of our results in terms of the group-velocity-dispersion- (GVD-) induced polarization dynamics of spatial solitary waves. In particular, we show that in media with normal GVD spatial symmetry breaking changes to polarization symmetry breaking when the relative strength of the cross-phase modulation exceeds a certain threshold value. The analytical and numerical stability analyses are fully supported by an extensive series of numerical simulations of the full model.     

Acoustic excitation of nuclear spin waves in the easy-plane antiferromagnetic material KMnF3

Ultrasound damping at T=4.2 K in single crystal easy-plane antiferromagnetic KMnF₃ is studied experimentally as a function of the magnitude and direction of a constant magnetic field H at frequencies of 640–670 MHz, corresponding to the frequencies of nuclear spin waves. Two experimental situations are examined: in the first, the vector H lies in the easy magnetization plane (001), and in the second, H forms an angle with (001). For longitudinal ultrasound waves propagating along the hard magnetization axis [001], it is found that the damping depends resonantly on the magnitude of the field H. In the first case a single damping maximum is observed, and in the second, two damping peaks that are well resolved with respect to the field. The angular dependence of the resonance damping signals on the direction of the constant magnetic field is found to have a 90° periodicity in all cases. The observed effects are explained by resonant ultrasonic excitation of nuclear spin waves. On the basis of an analysis of the magnetoacoustic interaction energy, it is shown that in the first case, nonzero oscillations of the antiferromagnetism vector L occur only in the basal plane, while in the second, oscillations of L occur both in the basal and a vertical plane, which are associated, respectively, with two branches of the nuclear spin waves. It is also shown that the 90° periodicity in the angular dependence of the damping signals is associated with a fourth order [001] axis. Zh. éksp. Teor. Fiz. 112, 1830–1840 (November 1997)     

Spin-wave spectrum of an ideal multilayer magnet upon modulation of all parameters of the Landau-Lifshitz equation

The spectrum of exchange spin waves in a multilayer magnet is theoretically investigated without regard for dissipation upon periodic modulation of all magnetic material parameters (uniaxial anisotropy constant, exchange interaction constant, saturation magnetization, gyromagnetic ratio) entering into the Landau-Lifshitz equation. A graphical method is proposed for analyzing the dependence of the propagation of spin waves on the depth of modulation of the material parameters. Practical application of the results obtained and the effect of dissipation on the propagation of spin waves in the system are discussed.     

Phase effects at second harmonic generation of powerful laser radiation in noncentrosymmetrical media

There has been developed the theory of second harmonic generation of the intensive laser fields in the existence of both quadratic and cubic polarization in medium in the constant-intensity approximation accounting for the reverse effect of the excited wave on the exciting one and simultaneously allowing us to take into account phase mismatch and the damping of all the interacting waves. It is shown that the changes of pump intensity through self-phase and cross-phase modulation processes effect optimum phase relationship between interacting waves, the change of the spatial beating period. The conditions of compensating undesirable phase shifts between interacting waves have been determined, the analytical expressions for calculation of optimum values of phase mismatch, length of noncentrosymmetrical medium and the spatial beating period are offered. It is shown that in the absence of linear phase mismatch with an increase of basic radiation intensity the spatial beating period is being reduced. The numerous analysis has been made of frequency doubling process efficiency for KDP and LiNbO₃ crystals.     

Magnetoacoustic resonance on nuclear spin waves in the cubic antiferromagnet RbMnF3

Magnetoacoustic resonance on nuclear spin waves is measured in the cubic antiferromagnet RbMnF₃. A resonance change with respect to a constant magnetic field H ₀ with maximum damping at H ₀≈4×10³ Oe is observed in the amplitude of an acoustic pulse passing through a sample owing to excitation of nuclear spin waves under nuclear magnetoacoustic resonance conditions. A study of the angular dependence of the damping revealed a 90° periodicity consistent with the fact that the [001] direction, around which the rotation takes place, is a four-fold axis of the crystal. An analysis of the dispersion law for nuclear spin waves shows that longitudinal ultrasound propagating along the [001] axis perpendicular to H ₀ excites a branch of nuclear spin waves whose frequency depends on the magnitude of the constant magnetic field. Fiz. Tverd. Tela (St. Petersburg) 41, 297–300 (February 1999)     

Spin-wave diffraction in a homogeneous ferromagnetic layer

The authors report theoretical and experimental research on diffraction effects associated with the excitation and propagation of surface spin waves. Expressions are derived for the Green's matrix of a point source of surface spin waves in the far-field region, and a simple scalar form of notation for the Green's function of a point source in an anisotropic medium is proposed. This form can be used to calculate the far diffraction field of an arbitrary planar antenna. The Green's functions obtained for the point source are used to calculate the radiation patterns of linear microstrip transducers, as well as the fraction of energy picked up by an analogous transducer positioned opposite the radiating transducer in the far-field region. The computational method is used to reduce the error in local monitoring of the quality of yttrium-iron garnet (YIG) films by the double-measurement method. The authors present the results of an experimental study of the dispersion characteristics of surface spin waves for different angles between andH _i, as well as a theoretical and experimental study of transducers that focus surface spin waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 32–48, April, 1989.The authors would like to thank S. G. Suchkov and Yu. A. Zyuryukin for valuable comments during a discussion of the results.     

Magnetic contributions to the low-temperature specific heat of the ferromagnetic insulator Pr 0.8 Ca 0.2 MnO 3

The Pr _1-x Ca_xMnO₃ system exhibits a ferromagnetic insulating state for the composition range x ? 0.25. A metallic ferromagnetic state is never realized because of the low hole concentration and the very small averaged A-site cation radius. In the present study, the nature of the magnetic excitations at low temperature has been investigated by specific heat measurements on a Pr _0.8 Ca_0.2MnO₃ single crystal. The decrease of the specific heat under magnetic field is qualitatively consistent with a suppression of ferromagnetic spin waves in a magnetic field. However, at low temperature, the qualitative agreement with the ferromagnetic spin waves picture is poor. It appears that the large reduction of the specific heat due to the spin waves is compensated by a Schottky-like contribution possibly arising from a Zeeman splitting of the ground state multiplet of the Pr³⁺ ions. Received 21 May 2001 and Received in final form 14 December 2001     

Collective effects in spin-polarized Boltzmann gases

As a result of an investigation of the real collision integral for paramagnetic atoms, we have obtained a criterion for propagation of spin waves in a spin-polarized Boltzmann gas. The main condition for propagation of weakly damped spin waves is a high anisotropy of the atomic scattering amplitude with predominance of the forward scattering. This condition is different from those suggested in earlier publications. Our results indicate that the range of paramagnetic gases where weakly damped spin waves can propagate at the room temperature is considerably wider than it was assumed previously. One example is vapors of alkali metals (Na, Cs, and Rb), where the degree of electron spin polarization can be very high. Zh. éksp. Teor. Fiz. 115, 865–876 (March 1999)