Dynamics of two-mode radiation in optical waveguides with strong mode coupling

Amplitude equations, as well as the effective dispersion and nonlinearity parameters, which define the dynamics of a wave packet formed by two strongly coupled modes, are derived with allowance for the frequency dependence of the linear mode coupling coefficient. These equations are used to study the onset of the modulation instability of the two-mode wave packet, soliton-like pulses, and compression modes. Unlike single-mode systems, the last two effects in optical waveguides may arise for both a negative and positive disper-sion of the waveguide material.     

Transformation and shift of a Gaussian light beam upon reflection from a resonant medium

The specific features of the transformation and shift of a Gaussian beam reflected from a resonant absorbing medium are analyzed numerically. The study is based on the expansion of the field of the incident Gaussian beam into plane-wave components by using the Fourier integral transform. The calculations are performed for a frequency range covering the resonance region. The conditions for the splitting of the profile of the reflected beam and for its negative shift are established.     

High-amplitude precession and dynamic unsusceptibility of magnetic moments of a two-layer film

The precession motion of magnetization in a longitudinal alternating magnetic field for a system of two antiferromagnetically coupled magnetoactive layers is studied. New dynamic modes characterized by large precession amplitudes and doubling of the period are found. The modes can be efficiently controlled using an external magnetic bias field. A new effect consisting in the unsusceptibility of a magnetic subsystem to excitation by an alternating field has been revealed.     

Modulation instability in systems of coupled waves with nonlinearity dispersion

Conditions for the appearance of modulation instability of an optical wave packet formed by one or two unidirectional strongly interacting waves are studied taking into account the influence of the temporal dispersion of a nonlinear response of the medium on this process. The regions of values of the frequency, input radiation intensity, and dispersion parameters in which the wave perturbations are increased are found. It is shown that the initial conditions for excitation of optical fibers of this type significantly affect the dynamics of the modulation instability.     

Influence of the surface anisotropy on the ground state of thin ferromagnetic films

A study is made of the ground state of a ferromagnetic film with a surface anisotropy which varies within wide limits from the easy-plane to the easy-axis type (– < 4) and with a bulk anisotropy of the easy-axis type ( 4). A rigorous analytic solution of the problem is given. The formulas obtained make it possible to calculate the distribution of the magnetization across the thickness of the film as a function of the parameters of the system. It is shown that there are two phase transitions from an inhomogeneous to a homogeneous state.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 71–76, July, 1980.The authors are grateful to B. A. Ivanov for his valuable comments and discussion of the results obtained.     

Equilibrium configurations and transitions between them in annular magnetic nanodipole systems

The equilibrium states of annular systems of magnetic dipoles have been studied by computer simulation. The bistability conditions under which the total magnetic moment of one of equilibrium configurations is zero, while the magnetic moment of another equilibrium configuration lies in the ring plane and is close to the sum of the magnetic moments of dipoles in the system, have been determined. The realization of other equilibrium configurations has also been demonstrated. We analyze transitions between equilibrium configurations by acting on the system by longitudinal and circular static fields, as well as transitions from the configuration with the maximal magnetic moment of the system to the configuration with zero total magnetic moment after the relaxation of oscillatory regimes excited by a varying field.     

Dispersion of Bulk Waves in a Graphene–Dielectric–Graphene Structure

Optics and Spectroscopy - We investigate the dispersion properties of the first waveguide modes in a dielectric film that is coated with graphene layers having different chemical potential values....     

Tunneling of Microwave Radiation through Three-Layer Structures Containing Ferrite Layer

Technical Physics - Tunneling of microwave radiation through a symmetric three-layer structure in which the central ferrite layer is interfaced with two layers of a material with negative...     

Amplification and generation of surface plasmon polaritons in a dielectric−HTS film−dielectric structure

Propagation of surface polaritons in the dielectric?HTS?dielectric structure is investigated in the temperature region of T <T _c/2, where the structure can be considered nonabsorbing. It is shown that in the region where the polariton wave is appreciably slowed down it can effectively interact with a flux of charged particles and be amplified due to the energy transfer from the drift current wave. It is also shown that a periodic substrate can cause generation of the surface polariton wave in the structure.     

Nonlinear Dynamics of a Two-Mode Wave Packet with Strong Linear Intermode

We investigate the dynamics of the wave packet formed by two codirected strongly interacting waves propagating in a medium with cubic nonlinearity. We obtain a soliton solution of the nonlinear Schrödinger equation in the degenerate case where the wave packet is described by a single partial momentum. In the nondegenerate case, we use the variational method to find the equation for the pulse duration, which turns out to be analogous to the equation for the coordinate in the Kepler problem. Solving it, we find the dependences of the pulse duration on the propagation distance in the cases of finite and infinite propagation regimes.