Single Pump Wave Research Articles

Role of convective cell in nonlinear interaction of kinetic Alfvén waves

Gyrokinetic particle simulations show that electrostatic convective cell (CC) can be generated by kinetic Alfvén waves and plays a dominant role in the nonlinear interactions underlying perpendicular spectral cascade. The CC growth rate increases linearly with the field amplitude of the pump waves and has a small but finite threshold, and decreases with the parallel wavevector. The CC growth is proportional to the perpendicular wavevector when there are two pump waves, but proportional to the square of the perpendicular wavevector when there is a single pump wave.

On temporal dynamics of Sn_2P_2S_6 oscillation in semi-linear cavity

Experimental measurements and calculations revealed an unusual type of oscillation dynamics of Sn(2)P(2)S(6) in the semi-linear cavity. It consists of a pronounced saw-tooth modulation of oscillation intensity--although it is not 100% in contrast--with the cw component being shifted in frequency with respect to the pump wave. This effect is attributed to the hybrid mode of two semi-linear oscillation geometries, one with a single pump wave and the other with two counterpropagating pump waves.

Spontaneous hexagon formation in photorefractive crystal with a single pump wave

A new scheme for spontaneous formation of hexagonal optical patterns in photorefractive crystals with dominant reflection gratings and a single pump wave is proposed and realized experimentally. It is shown theoretically that spontaneous hexagon formation results from random small-angle scattering of the pump wave inside the crystal. The threshold of spontaneous hexagon formation is found.

Theory of optical phase conjugation in disordered media: Coherent properties of the backscattered field.

Recently it was shown that in disordered media, nonlinear backscattering of phase-conjugated signal light is possible in the presence of only a single pump wave, in contrast to the case of an ordered medium where two counterpropagating pump waves are necessary. Formally, this disorder-induced nonlinear process corresponds to the cooperon-channel (back)scattering of the signal wave in the presence of diffusion propagation of the pump wave. (The cooperon is the Cooper particle-particle diffusion propagator.) In this contribution, the question is considered whether the disorder-induced backscattering of phase-conjugated light can restore the disturbed signal wave front as it does in the ordered case. Examining correlations of the outgoing waves corresponding to different incoming signal waves, it is shown that the backscattered waves possess a ``phase memory'' even for a large difference of the angles of incidence of incoming waves. This is in contrast to the case of linear backscattering, where such correlations take place only at a very small difference of the angles of incidence (of the order of backscattering peak width). Thus the phase conjugation in disordered media does possess the peculiar coherent properties of that in ordered media.

Theory of phase conjugation of light in disordered nonlinear media.

In the case of disordered nonlinear media, it is shown that in four-wave mixing a phenomena analogous to phase conjugation may occur. In contrast to the case of transparent media in which two counterpropagating pump waves (with frequency ${\ensuremath{\omega}}_{p}$) are required, phase conjugation may occur in the presence of a single pump wave injected into the disordered nonlinear material. We find that in the angular distribution of radiation of frequency ${\ensuremath{\omega}}_{s}$ (${\ensuremath{\omega}}_{s}$=2${\ensuremath{\omega}}_{p}$-${\ensuremath{\omega}}_{i}$, where ${\ensuremath{\omega}}_{i}$ is the frequency of probe wave) there is a narrow peak in the backscattered direction associated with the probe wave. The intensity of this peak may be some orders of magnitude larger than the diffuse background at the frequency ${\ensuremath{\omega}}_{s}$.

Weak localization and disorder induced phase conjugation of light

It is shown that the phase conjugation phenomenon may occur at multiple scattering of light in presence of a single pump wave injected into the disordered nonlinear medium. We find that in the angular distribution of generated light there is a narrow peak in the backscattered direction (with respect to the probe wave). The intensity of this peak may be considerably larger than the diffuse background at the same frequency.

Nonlinear behaviour of a finite amplitude electron plasma wave - II. Wave–wave interactions

Nonlinear behaviour of plasma due to resonant three-wave interactions is considered, both as a decay instability arising from a single pump wave and as resonant mixing when two waves are initially present in the plasma. Observations of both processes involving longitudinal electron (Lang-muir) waves and ion waves are reported and quantitative measurements given. The interaction between coherent waves is related to that between random-phase waves and in this way the cross-section for plasmon-plasmon interaction derived. In a finite plasma, resonant three-wave interactions in which all waves are Langmuir waves are possible and quantitative results for this process are given. The new results of this paper and an earlier one are summarized and combined in relation to the dispersion diagram of Langmuir waves.

Parametric interaction in electron beam waves—A system function characterization

In this paper we develop a technique for characterizing parametric interaction in electron beam waves in terms of a system transfer function. We consider systems in which the parametric interaction is described by a matrix equation of the form (∂/∂t + u <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> ∂/∂ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</inf> )a = -iH a where a is a state vector of the system and H is the matrix characterizing the interaction. Solutions in the time domain can be expressed in the form a(z, t) = M(z, t) a(O, t - z/u <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> ) where M (a matrix) is called the system function in the time domain. Solutions in the frequency domain can be expressed in the form â(z, ω) = ∫ M(z, ω - ω')â(O, ω')dω' where â(z, ω) is the Fourier transform of a(z, t) and M(z, ω) is the transform of M(z, t). Solutions for parametric interaction in transverse beam waves are worked out for two cases: In Case I we derive the well-known result that describes the behavior of a single pump wave, electron beam parametric amplifier. In Case II we consider a parametric interaction involving two pump waves in which an infinite number of frequencies are parametrically coupled.