Four-wave Parametric Processes Research Articles

Analysis of the broadband chaotic spin-wave excitations in an active ring oscillator based on a metalized ferrite film

This paper reports the first experimental study of broadband chaotic nonlinear spin- wave excitations which is formed through development of four-wave parametric processes in active ring oscillator based on metallized ferrite film. We find that an increase in the oscillation power leads to Hopf bifurcations sequence. Monochromatic, periodic quasi-periodic and chaotic excitations are observed. Spectra of the chaotic excitations consist of series of chaotic bands separated well in frequency. Parameters of the chaotic attractors are discussed.

Monoclinic m-LaVO4—a novel high Raman gain SRS-active crystal

Monoclinic m-LaVO4, having a monazite-type structure and being known as a host crystal for Nd3+-lasants, is an attractive χ(3)-nonlinear optical material for Raman laser converters. This paper presents the stimulated Raman scattering (SRS) spectroscopy of m-LaVO4 in the visible and near-IR spectral range using picosecond laser excitation. High-order SRS and Raman-induced four-wave parametric mixing processes result in an almost two-octave-wide Stokes and anti-Stokes frequency comb. All the measured spectral lines were assigned to the participating molecular vibration modes of the studied vanadate. Finally, an estimation of the steady-state Raman gain coefficient for first Stokes generation in near-IR was performed.

Observation of the modulation instability and spin wave solitons in ferromagnetic films under the conditions of coexistence of four-wave and three-wave parametric processes

Nonlinear phenomena that arise during the propagation of spin waves in thin ferromagnetic films under conditions of the simultaneous existence of three-wave and four-wave parametric processes have been investigated. Investigations have been performed for single-frequency and double-frequency regimes of excitation of intense spin waves. The spontaneous modulation instability of the monochromatic running spin wave has been revealed for the first time at frequencies at which three-wave decay processes are allowed. The pronounced generation of a periodic sequence of bright spin wave solitons has been observed under excitation of two monochromatic spin waves at the same frequencies.

Nonlinear response of ferromagnetic film resonator under conditions of nonlinear damping of magnetization oscillations

Nonlinear response of a tangentially magnetized ferromagnetic film resonator has been experimentally studied under the conditions where the nonlinear effects in the resonator are related to four-wave parametric processes. It is shown that an increase in the microwave power supplied to the resonator leads to a nonlinear shift of the eigenfrequencies and broadening of the resonant absorption peaks. The latter phenomenon is related to the nonlinear damping of magnetization in the resonator. It is established that the nonlinear shift of the frequency is thresholdless, while the nonlinear damping has a threshold, the appearance of which also leads to limitation of the nonlinear shift of the resonator frequency.

Four-wave parametric processes in multicascade SRS conversion of neodymium laser radiation into an eye-safe region

Four-wave parametric processes in multicascade SRS conversion of neodymium laser radiation into an eye-safe region are studied in relation to the phase mismatch of parametric coupling, which is determined by the refractive index dispersion of the SRS medium. The numerical simulation showed that the generation of multicascade SRS at a particular wavelength in the IR region can be even more efficient than the single-cascade conversion if the parametric coupling between the first Stokes and anti-Stokes components is weak and higher Stokes components are strongly parametrically coupled with each other. This situation is observed in the eye-safe IR region, where the refractive index dispersion of solid-state SRS media is minimal, which allows one to optimize the SRS conversion by choosing an SRS medium and its length.

Self-Generation of Chaotic Solitary Spin Wave Pulses in Magnetic Film Active Feedback Rings

The chaotic self-generation of short solitary spin wave pulses has been observed for the first time. The pulses were produced from parametrically excited spin waves in an yttrium-iron-garnet film in an active feedback ring under conditions where both three-wave and four-wave parametric processes were allowed. The power-frequency spectrum was broadband and chaotic.

Theoretical and Numerical Simulation Investigation of Parametric Processes Associated with Up-shifted Ionospheric Stimulated Radiation

Stimulated Electromagnetic Emission SEE produced by heating the earth's ionosphere with high powered radiowaves is currently a topic of significant interest in ionospheric modification physics since it has tremendous potential as an ionospheric diagnostic tool. SEE is also a fundamental nonlinear process in plasma physics that is not currently well understood on a theoretical basis. SEE is believed to be produced by nonlinear wave-wave interactions involving the electromagnetic and electrostatic plasma waves in the altitude region where the pump wave frequency is near the upper hybrid resonance frequency. The most prominent up-shifted feature in the SEE spectrum is the broad up-shifted maximum BUM. From characteristics of this feature, a four-wave parametric decay process has been proposed as a viable mechanism for its production. The object of this work is to (1) investigate the nonlinear development of the four-wave decay instability by using theoretical and numerical simulation models and (2) access its possible role in the production of the BUM spectral feature. Results of this investigation show that there is good agreement between predictions of the proposed theoretical model and the numerical simulation experiments. The simulation frequency spectrum exhibits many of the important features of the experimental observations. The numerical results show that consideration of the full nonlinear development of the four-wave parametric instability is crucial in providing insight into the asymmetric nature of the wave frequency spectrum observed during the experiments.

Quasi-rotational spectral structure of optical radiation due to stimulated Raman scattering and parametric processes in high-pressure hydrogen

Optical radiation from IR to UV with a quasi- rotational spectral structure was obtained, when 1:06-mm lin- early polarized pulses of duration 30 ps and energy 40 mJ were focused into a cell filled with hydrogen under high pres- sure. A luminous channel of up to 12 cm in length was ob- served in the focal region. The quasi-rotational lines exhibit a substructure made up of components produced in hydrogen by the combined action of stimulated vibrational and rota- tional Raman scattering and cascaded four-wave parametric processes. In the visible, the integral energy of each spectral line does not differ greatly from the average value of 10 mJ.

Parametric frequency conversion with amplification of a weak spin wave in a ferrite film

We report on experiments of parametric frequency conversion of a weak signal spin wave by a copropagating strong pump spin wave. An effective spin-wave frequency conversion with amplification occurred when the carrier frequencies of the co-propagating waves were in the spectral region of high negative dispersion in the dipole-exchange spin-wave spectrum of the film. A theoretical explanation of the observed phenomenon is given in terms of a four-wave parametric interaction process.

Theoretical and simulation studies of broad up‐shifted sideband generation in ionospheric stimulated radiation

A second order four‐wave parametric process proposed to be responsible for the generation of the broad up‐shifted sideband in ionospheric stimulated radiation is studied by using a theoretical model and one dimensional electrostatic particle‐in‐cell simulations. The results indicate that (1) the initial evolution in nonlinear simulations is well described by the proposed theoretical model, (2) the simulation frequency power spectrum in a saturated nonlinear state exhibits important characteristics of the experimental observations and (3) the full nonlinear evolution of this four‐wave process is crucial in interpreting the asymmetric nature of the wave frequency spectrum observed during experiments.

Nonlinear alignment between conical emissions generated in a four-wave parametric mixing process

P levels. A numerical model developed to describe mechanisms involved in the conical emission generation processes indicates that the saturation observed is due to the opposite angular tuning of the near-infrared and yellow conical emission generated in the same process. The mechanisms responsible are assigned to (self)induced phase modulation processes of the waves involved.

Spectral and spatial evolution of a conical emission in Na vapor

A detailed study on yellow conical emission observed in dense sodium vapor following near-resonant one-photon excitation of the Na 42P levels was performed. The origins of conical emission are suggested to be due to Raman resonant four-wave parametric mixing processes. In order to describe spectral and spatial features of off-axis emission, we introduce self-phase modulation and induced-phase modulation as important additional nonlinear processes, explaining the nonmonotonic detuning of the wavelength of the conical radiation with the exiting laser wavelength in the vicinity of resonance transitions. The spatial evolution of emission generated via four-wave mixing is modeled by solving the two-dimensional nonlinear Schrodinger equation describing the spatial evolution of light beams in a nonlinear media. Experimental and theoretical results are presented and discussed.

Parametric Amplification of Propagating Spin Waves in Ferrite Films

Amplification of a weak signal spin wave by a strong pump spin wave propagating in yttrium iron garnet film was observed for the first time. A theoretical explanation of this effect is given on the basis of the four-wave parametric processes.

Observation of parametric amplification of propagating dipole-exchange spin waves in yttrium iron garnet films

Amplification of a weak-signal spin wave by a strong pump spin wave propagating in an yttrium iron garnet film is observed for the first time. A theoretical explanation of the amplification phenomenon is suggested on the basis of the four-wave parametric processes.

Acousto-optic modulation in diffusive semiconductors

The modulation of an intense electromagnetic beam induced by the acousto-optic (AO) effect has been analyzed in a strain-dependent semiconductor crystal. The effect of the diffusion of charge carriers due to the doping of the medium has been investigated using the coupled-mode theory. The origin of the AO interaction is assumed to lie in the induced nonlinear current density of the medium. The AO modulation process has been treated as a four-wave parametric mixing process and the effective third-order acousto-optic susceptibility characterizing the instability process has been deduced. The AO modulation is greatly modified by propagation characteristics such as dispersion and diffraction due to dielectric relaxation of the acoustic mode. The threshold characteristics and the steady state growth rates are estimated from the acousto-optic polarization of the medium. Analytical estimation reveals that the modulated beam can be amplified in a dispersionless acoustic wave interaction regime in the presence of enhanced diffusion due to excess charge carriers. The relative magnitude of the pump field at various doping levels exhibits entirely different steady-state gain characteristics. A particular pump field Er exhibits maximum gain in the lightly doped regime while the same field exhibits a minimum due to reverse energy flow from electromagnetic fields to the collision dominated space-charge field in a heavily doped medium. At very high densities with the electron plasma frequency of the medium close to the pump frequency or under the influence of very high (drift) pump field the acoustoelectric domains are washed out due to domination of the drift process over diffusion instability process. This leads either to gain saturation in lightly doped regime or explosive increment of the gain constant in heavily doped regime. The magnitude of the third-order nonlinear optical susceptibility for III-V semiconductors obtained from our theoretical analyses is found to agree well with the previously reported values.

Relativistic and nonrelativistic modulational instability of a laser radiation in an unmagnetized laser-produced plasma: Kinetic theory

This paper presents a rigorous theoretical investigation of the relativistic and nonrelativistic modulational instability of a high-power laser radiation propagating in a collisionless and unmagnetized laser-produced plasma. The kinetic equationviz. the relativistic Vlasov equation has been employed to find the nonlinear response of electrons for this four-wave parametric process in the plasma. The actual motivation behind this theoretical investigation is to find the relativistic effect on this four-wave paremetric processviz. the modulational instability. Here, it can be noted that the modulational instability of the laser radiation under our situation has not a large but considerable relativistic effect and for the same set of plasma parameters the growth rate of the instability in ultrarelativistic consideration is approximately three times higher than that in the nonrelativistic consideration.

Parametric decay of an electron-Bernstein wave excited by the optical mixing of two microwave beams

Nonlinear theory of an electron-Bernstein wave at lower-hybrid frequency is developed. Fluid theory is applied for the excitation of a lower-hybrid wave whereas a kinetic model is used for the electron-Bernstein mode as fluid theory breaks down for short-wavelength perturbations, and the propagation of these waves depends upon the cyclotron motion of the electrons about the field lines. The nonlinearity arises because of electrons motion, introduced through ponderomotive force. The electron-Bernstein wave is assumed to be excited by optical mixing of two microwave beams. The nonlinear dispersion relation and growth rates are calculated for three-wave and four-wave parametric interaction processes. Since the electron-Bernstein wave is nonlinearly excited by two intense beams, there is no power threshold and the excited power increases proportionally to the product of the incident powers. The investigation appears to be of great potential because of recent significant developments in gyrotron technology.

Transport due to ηi modes in the presence of radiofrequency fields

The influence of a radiofrequency (RF) wave in the ion cyclotron range of frequencies (ICRF) on the toroidal ion temperature gradient driven drift mode (ηi mode) is presented. The four-wave parametric process involving a fast magnetosonic source wave and ion cyclotron sidebands is considered. Explicit expressions for the non-linear growth rate and the associated ion thermal conductivity are derived. The stability and transport properties are found to be sensitive to the sign of, where and are the pump and the ηi mode wave vectors, respectively.

Dynamic chaos in the case of parametric interactions of light waves

An investigation is made of the spatial evolution of a system of constant-frequency light waves, each of which participates in two four-wave parametric interaction processes simultaneously. It is shown that the competition between the parametric processes may result in spatial chaos. The chaotic evolution regime is established if the wave amplitudes at the boundary of a nonlinear medium differ sufficiently from the values corresponding to an integrable limit, the existence of which depends on the symmetry of the system. The other condition for the appearance of chaos—strong interwave energy exchange—is obeyed when the parameters of the medium and of the radiation are of the same orders of magnitude as in the case of reflection accompanied by amplification in phase conjugation of a laser radiation wavefront on the basis of a degenerate four-wave mixing. The characteristic features of the appearance of a stochastic instability of a system of interacting light waves under experimental conditions are considered.

Theory of transient hyper-Raman scattering in gases

A theory is developed for transient hyper-Raman scattering and four-wave parametric processes in a gaseous medium subjected to an ultrashort pump pulse field. Investigations are made of the intensity and spectrum of the infrared and ultraviolet radiation generated in a medium as a result of these processes, bearing in mind the transient properties of the pump (phase modulation, pulse profile). It is shown that the initial nonlinearity of the pump field and the parametric processes result in new effects not observed in transient stimulated Raman scattering. For a large two-photon detuning, the hyper-Raman forward scattering is suppressed because of destructive interference with stimulated parametric generation of ultraviolet radiation. The gain of the infrared and ultraviolet radiation depends on the pump pulse profile. Under exact two-photon resonance conditions in the absence of any phase modulation of the pump, infrared and ultraviolet pulses are coherently split into various subpulses and a time-dependent Autler–Townes doublet is observed in their spectrum.