Observation Of Nonlinear Phenomena Research Articles

Nonlinear optical effects in epsilon-near-zero media

Efficient nonlinear optical interactions are essential for many applications in modern photonics. However, they typically require intense laser sources and long interaction lengths, requirements that often render nonlinear optics incompatible with new nanophotonic architectures in integrated optics and metasurface devices. Obtaining materials with stronger nonlinear properties is a crucial step towards applications that require lower powers and smaller footprints. Recently, a new class of materials with a vanishing permittivity, known as epsilon-near-zero (ENZ) materials, has been reported to exhibit unprecedented ultrafast nonlinear efficiencies within sub-wavelength propagation lengths. In this Review, we survey the work that has been performed on ENZ materials and the related near-zero-index materials, focusing on the observation of various nonlinear phenomena (such as intensity-dependent refraction, four-wave mixing and harmonic generation), the identification of unique field-enhancement mechanisms and the study of non-equilibrium dynamics. Degenerately doped semiconductors (such as tin-doped indium oxide and aluminium-doped zinc oxide) are particularly promising candidates for ENZ-enhanced nonlinear optical applications. We conclude by pointing towards possible future research directions, such as the search for ENZ materials with low optical losses and the elucidation of the mechanisms underlying nonlinear enhancements. Materials with vanishingly small dielectric permittivity, known as epsilon-near-zero materials, enable strong ultrafast optical nonlinear responses within a sub-wavelength propagation length. This Review surveys the various observations of nonlinear phenomena in this class of materials.

Three-Dimensional Instability of Opposite Polarity Nonthermal Dusty Plasma

Abstract Nonlinearity properties of obliquely wave propagation and instability in collisionless magnetized nonthermal dusty plasmas containing fluid of negative-positive grains are investigated. Zakharov-Kuznetsov equation is obtained and the three-dimensional wave instability is studied. The parameters such as polarity charge ratio, cyclotron frequency and fast nonthermal effectiveness of the instability properties and growth rate are theoretically studied. It is found that both positive and negative soliton profiles are formed depending on the fraction ratio of electron-ion nonthermality. Also, the growth rate was dependent nonlinearly on the direction cosines, the cyclotron frequency and the positive (negative) grain charge ratio, but independent of the fractional ratio of electron-ion nonthermality. Present discussion may be very significant regarding the observations of nonlinear phenomena in space.

Nonlinear Pulse Propagation and Modulation Instability in Periodic Media with and without Defects

The nonlinear propagation of EMW in periodic media is of great interest due to the possibility to accumulate energy in periodic media within the stop band and, therefore, the input intensity levels for observation of nonlinear phenomena are quite low [1]. For resonant interactions, also it is possible to realize matching conditions, which are not possible in uniform media. Both resonant multiwave interactions and selfaction of EMW in nonlinear periodic media have been analyzed [1, 2]. Also, a method based on a slow variation in time was proposed, which seems more adequate than others based on coupled equations [3]. The presence of defects in periodic structure leads to narrow regions of transmission within the stop-band. In this case, the application of coupled equations for counter propagating waves becomes doubtful, and a more general approach is needed [3]. Also, the influence of defects on the dynamics of modulation instability of long pulses is of a great interest. The present paper considers numerical simulations of the pointed above phenomena. For a correct description of the nonlinear dynamics, it is necessary also to take into account the wave dissipation and possible transverse diffraction. The results of simulations demonstrated the essential influence of defects within the periodic structure on the nonlinear propagation of EM pulses, even if the carrier frequency is chosen within the stop band of the structure with a defect. This fact can be explained by a quite wide spectrum of the input pulse, and the “tail” of such a spectrum is within the transmission region due to the defect. This situation is analogous to the nonlinear propagation of short spin-dipole waves in the vicinity of the cut-off frequency [4]. The dynamics of modulation instability also changes in the presence of the defect. The diffraction can affect essentially the modulation instability dynamics.

Observation of nonlinear phenomena in ferromagnetic transmission resonance

In this paper we present the nonlinear effects we obtained so far through ferromagnetic-transmission-resonance experiments in iron and nickel. The experiments were performed in the geometry in which both the applied and microwave fields are mutually parallel and also parallel to the sample surface at the input cavity. In this geometry, we have found two interesting transmitted waves through ferromagnetic samples several microns thick. One is polarized parallel to and has the same frequency as the applied microwave field. The other, polarized perpendicular to the applied field, has a frequency half that of the applied field and is generated in the ferromagnetic sample. The results are compared to the nonlinear theory presented in the previous paper. The agreement between the experimental and theoretical results is reasonable. The theory shows that the nonlinear phenomena are very sensitive to the exchange stiffness constant. It is thus hoped that these phenomena will be useful in determining the exchange stiffness constant, and ultimately the exchange integral, as a function of temperature. Further, they might provide new information on spin-relaxation processes.