Four-wave Interaction Processes Research Articles

Correlation-Enhanced Interaction of a Bose-Einstein Condensate with Parametric Magnon Pairs and Virtual Magnons.

Nonlinear interactions are crucial in science and engineering. Here, we investigate wave interactions in a highly nonlinear magnetic system driven by parametric pumping leading to Bose-Einstein condensation of spin-wave quanta-magnons. Using Brillouin light scattering spectroscopy in yttrium-iron garnet films, we found and identified a set of nonlinear processes resulting in off-resonant spin-wave excitations-virtual magnons. In particular, we discovered a dynamically strong, correlation-enhanced four-wave interaction process of the magnon condensate with pairs of parametric magnons having opposite wave vectors and fully correlated phases.

Squeezing in the Difference of the Fields in Degenerate Four-and Five-wave Interaction Processes

Squeezing in the difference of the fields in degenerate four- and five-wave interaction processes is studied. It is shown that the difference squeezing can be led to normal squeezing of the field for uncorrelated modes. It is found that the amplitude-squared squeezing of the fundamental mode directly converted into the normal squeezing of the signal mode in the four-wave interaction process and amplitude-cubed of the fundamental directly converted into the normal squeezing of the signal mode in the five-wave interaction process. Detection of higher-order squeezing in these processes is also studied. It is observed that difference squeezing responds nonlinearly to the number of pump photons and found greater in the stimulated process than in spontaneous one. Difference squeezing exists only in certain domain value of pump photons. It is inferred that the multi-photon absorption process is more suitable for the generation of optimum squeezed light.

Generation and detection of whistler wave induced space plasma turbulence at Gakona, Alaska

We report on high-frequency wave injection experiments using the beat wave technique to study the generation of very-low-frequency (VLF) whistler waves in the ionosphere above Gakona, Alaska. This work is aimed at investigating whistler wave interactions with ionospheric plasmas and radiation belts. The beat wave technique involves injecting two X-mode waves at a difference frequency in the VLF range using the High-frequency Active Auroral Research Program (HAARP) heating facility. A sequence of beat wave-generated whistler waves at 2, 6.5, 7.5, 8.5, 9.5, 11.5, 15.5, 22.5, 28.5 and 40.5 kHz were detected in our 2011 experiments. We present Modular Ultra-high-frequency Ionospheric Radar (MUIR) (446 MHz) measurements of ion lines as the primary diagnosis of ionospheric plasma effects caused by beat wave-generated whistler waves. A magnetometer and digisonde were used to monitor the background ionospheric plasma conditions throughout the experiments. Our theoretical and data analyses show that VLF whistler waves can effectively interact with ionospheric plasmas via two different four-wave interaction processes leading to energization of electrons and ions. These preliminary results support our Arecibo experiments to study NAU-launched 40.75 kHz whistler wave interactions with space plasmas.

Whistler wave-induced ionospheric plasma turbulence: Source mechanisms and remote sensing

We report a series of experiments conducted at Arecibo Observatory in the past, aimed at the investigation of 40.75kHz whistler wave interactions with ionospheric plasmas and the inner radiation belts at L=1.35. The whistler waves are launched from a Naval transmitter (code-named NAU) operating in Aguadilla, Puerto Rico at the frequency and power of 40.75kHz and 100kW, respectively. Arecibo radar, CADI, and optical instruments were used to monitor the background ionospheric conditions and detect the induced ionospheric plasma effects. Four-wave interaction processes produced by whistler waves in the ionosphere can excite lower hybrid waves, which can accelerate ionospheric electrons. Furthermore, whistler waves propagating into the magnetosphere can trigger precipitation of energetic electrons from the radiation belts. Radar and optical measurements can distinguish wave–wave and wave–particle interaction processes occurring at different altitudes. Electron acceleration by different mechanisms can be verified from the radar measurements of plasma lines. To facilitate the coupling of NAU-launched 40.75kHz whistler waves into the ionosphere, we can rely on naturally occurring spread F irregularities to serve as ionospheric ducts. We can also use HF wave-created ducts/artificial waveguides, as demonstrated in our earlier Arecibo experiments and recent Gakona experiments at HAARP. The newly constructed Arecibo HF heater will be employed in our future experiments, which can extend the study of whistler wave interactions with the ionosphere and the magnetosphere/radiation belts as well as the whistler wave conjugate propagation between Arecibo and Puerto Madryn, Argentina.

Parametric instability producing broad symmetrical structure in the spectrum of ionospheric heating-induced radiation

A four-wave interaction process in which an O-mode electromagnetic pump decays parametrically into a lower hybrid decay mode and two-electron Bernstein sidebands is analyzed. It is shown that the instability can be excited in a spatial region near the electron Bernstein/upper hybrid double resonance and in a narrow pump frequency range slightly below the third harmonic electron cyclotron resonance. The two electron Bernstein sidebands have about the same intensity and thus, produce Broad Symmetrical Structure (BSS) in the emission spectrum after being converted into electromagnetic radiation by scattering off background field-aligned density irregularities. The results also show that the size of the instability zone becomes very small as the pump frequency operates near a cyclotron harmonic higher than the third. Thus, the converted emission will be too weak to be detected. This explains why the BSS feature in the spectrum of stimulated electromagnetic emissions (SEEs) has only been observed in the third harmonic case.

Nonlinear Microwave Phenomena in Ferrite Films : Basic Physics and Applications (Invited)

A short overview of the theory and applications of nonlinear spin wave phenomena in ferrite films at microwave frequencies is given. A method of classical Hamiltonian formalism for spin waves in bulk ferrimagnets in combination with the theory of spin wave spectrum for thin magnetic films is used for theoretical description of nonlinear spin wave phenomena in films. Comparative roles of three-wave and four-wave interaction processes in the nonlinear dynamics of spin waves in films are discussed. A local character of spin wave excitation by the magnetic field of a strip-line antenna is taken into account. Several examples of nonlinear microwave signal processing devices based on the nonlinear dynamics of spin waves in ferrite films (frequency-selective limiter, signal-to-noise enhancer, convolver, and a soliton delay line) are presented.

Quantum theory of the resonance interaction of an intense monochromatic electromagnetic wave with arbitrary polarization composition

A theory describing the absorption and emission spectra of an atomic transition in the field of an intense monochromatic wave with arbitrary polarization composition is developed. The theory includes a quantum description of forward-directed four-wave interaction processes. Expressions are obtained for describing the absorption and emission spectra in transitions adjacent to the working transition. The description developed includes the perturbation of the atomic subsystem by a constant magnetic field. The spectral characteristics, polarization composition, and angular distribution of the resonance fluorescence are investigated. The nonlinear Faraday effect and the properties of resonance fluorescence are investigated for the transition J=1→J=0.

Phase-matching considerations of four-wave interaction processes in biaxial crystals

In light of the principle of phase matching (PM) in biaxial crystals, PM types for four-wave interaction processes are discussed. The relationships among the refractive indices of the four interacting waves are analyzed to classify PM topologies. A computer program is developed to characterize and obtain PM directions and their loci. As examples, PM loci for direct third-harmonic generation in four biaxial crystals are presented.

Four-wave interaction phenomena contributing to holographic scattering in LiNbO<inf>3</inf>and LiTaO<inf>3</inf>

Experimental results are presented which indicate the importance of four-wave interactions for holographic scattering. In contrast to three-wave interactions there are no changes in the polarization of the scattered beams. But similar to three-wave interactions the rays are scattered in a cone emerging in the forward and backward directions from the sample. The cone angle is equal to the angle of reflection at the rear side of the sample. Reflected rays are necessary to initiate the scattering process. We present an explanation for the geometry of the pattern produced by the incident, reflected, and scattered beams. Furthermore, experimental results on the angular and time dependence of the scattered radiation are given for LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> :Fe and LiTaO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> :Fe crystals, demonstrating the predominance of four-wave interaction processes.

Observation of Acoustically Induced Phase-Matched Optical Harmonic Generation in GaAs

Radiation near 5.3 \ensuremath{\mu}m arising from the collinear phase-matched mixing of a 10.6-\ensuremath{\mu}m $Q$-switched laser beam and a pulsed ultrasonic shear wave has been observed in GaAs. Phase matching occurs when the crystal momentum of the acoustic phonon is adjusted to equal the familiar momentum mismatch observed in conventional second-harmonic generation in cubic GaAs. Three components of the susceptibility governing the four-wave interaction process were measured.