Shuttle wave experiments

Wave experiments on shuttle are needed to verify dispersion relations, to study nonlinear and exotic phenomena, to support other plasma experiments, and to test engineering designs. Techniques based on coherent detection and bistatic geometry are described. New instrumentation required to provide modules for a variety of missions and to incorporate advanced signal processing and control techniques is discussed. An experiment for Z to 0 coupling is included

Double accumulation and anisotropic transport of magneto-elastic bosons in yttrium iron garnet films

Interaction between quasiparticles of a different nature, such as magnons and phonons in a magnetic medium, leads to the mixing of their properties and the formation of hybrid states in the areas of intersection of individual spectral branches. We recently reported the discovery of a new phenomenon mediated by the magnon-phonon interaction: the spontaneous bottleneck accumulation of magneto-elastic bosons under electromagnetic pumping of pure magnons into a ferrimagnetic yttrium iron garnet film. Here, by studying the transport properties of the accumulated magneto-elastic bosons, we reveal that such accumulation occurs in two frequency-distant groups of quasiparticles: quasi-phonons and quasi-magnons. They propagate with different speeds in different directions relative to the magnetization field. The theoretical model we propose qualitatively describes the double accumulation effect, and the analysis of the two-dimensional spectrum of quasiparticles in the hybridization region allows us to determine the wavevectors and frequencies of each of the groups

Nonreciprocal Electromagnetics of Layered Media

In plasmonic systems, interaction of light and surface plasmons leads to excitation of surface plasmon polaritons (SPPs) carrying energy on the surface. In an isotropic plasmonic system, the SPPs optical response is reciprocal, which means that the forward and backward surface waves have identical propagation behaviors and SPPs refract when they encounter a discontinuity on the surface. In order to excite SPPs resilient to the surface disorders, the system reciprocity needs to be broken by different techniques such as applying an external magnetic bias. In this case, the plasmonic system becomes a gyrotropic medium. Recently, it has been shown that magnetized continuous plasmonic systems such as semiconductors and graphene support unidirectional SPPs, the surface waves that are propagating only in one direction and are robust to the surface impurities. This topic has attracted the attention of many researchers, including our group. In this work, we study the properties of unidirectional SPPs in different plasmonic configurations. Our findings set a solid foundation for future active nonreciprocal plasmonic devices based on unidirectional SPPs. First, we study SPPs in the well-known topological Voigt configuration. Since indium antimonide (InSb) crystal is often cited as a suitable magneto-optics platform that supports unidirectional SPPs, we evaluate the functionality of this crystal as a topological platform by considering realistic conditions. So, using the far-field time-domain THz spectroscopy measurement, our group, along with colleagues at the University of West Virginia, examine the magneto-optical effects of the undoped InSb crystal at different temperatures varied from 5K to 300K. We apply a multi-carrier material model to consider the effect of both electrons and holes charge carriers. Then, using the measured data we examine the unidirectional SPPs and discuss the constrains that limit applications. We design a grating metallic coupler on the surface of the magnetized InSb to launch unidirectional SPPs. The measured reflection data reveals strongly nonreciprocal SPPs that are tunable by temperature and magnetic field intensity. The patterned InSb sample is tilted to examine topological behavior. The measured data are consistent with the theoretical predictions. Next, via simulation we study unidirectional SPPs on the surfaces of a magnetized plasma slab coated by a dielectric material below the plasma frequency. The equi-frequency contours are extracted from dispersion surface which follows by obtaining the group velocity vectors to estimate the SPP propagation behaviors at different operation frequencies. We mainly focus on a frequency window wherein there exists narrow-beam unidirectional SPPs. We present a Green\u27s function model for a gyrotropic slab to examine the effect of thickness on the narrow SPP beams. We observe that when the slab is thin, in addition of two excited narrow beams at the top interface, two other narrow beams form at the bottom interface due to energy coupling. We characterize them by an asymptotic dispersion relation derived from a quasi-static approach. Then, we study the nonlocality effects and Chern numbers in a continuous plasma medium. Topological SPPs are characterized by integer Chern invariants. When a continuous plasma systems is model by the (overly simplistic, but often used) local Drude model, there is a dispersion band that is ill-behaved at large wavenumbers and assigned by a non-integer Chern number. In this case, the number of unidirectional edge modes cannot be determined using the bulk-edge correspondence principle. This problem has been previously solved by introducing an ad hoc material model which includes a spatial cutoff wavenumber in the model. However, the proposed nonlocal model leads to some difficulties such as non-realistic material response at large wavenumbers and the need to interpolate the interfaced materials so that the Chern numbers sum to zero as they must. To overcome this issue, we instead suggest applying the hydrodynamic material model which is a more realistic, physical, nonlocal model. In this case, we evaluate the Chern numbers and dispersion bands. We show that this model form a complete, self consistent model that clarifies the topological physics of plasma continua. In the next work, we propose a new plasmonic configuration to excite nonreciprocal curved SPPs. We demonstrate that by applying radial bias in a plasma system, one-way SPPs travel on a circular path, unlike in an axially-biased system which supports SPPs with linear trajectory. We derive a Green\u27s function model for a radially-biased plasma system to examine curved SPPs. A nonreciprocal circular junction is proposed to effectively guide SPPs on the curvature. Finally, we examine the unidirectional SPPs in two-dimensional plasmonic platform. It has been previously shown that graphene monolayer biased by external magnets supports unidirectional edge modes. Here, we evaluate the magneto-optical effects of graphene/chromium triiodide (CrI3) heterostructure. The exchange field between layers provides an effective out of magnetic field. The optical conductivity is a tensor with non-zero off-diagonal elements which manifest the nonreciprocal response. We obtain one-way edge modes and Faraday rotation in this multi-layer structure. However, we argue that the nonreciprocal response of this heterostructure is weaker than the isolated graphene biased by external magnets. Therefore, CrI3 magnetic monolayer does not work as an alternative magnetic source that causes strong non-reciprocity

Hybrid resonance and long-time asymptotic of the solution to Maxwell's equations

We study the long-time asymptotic of the solutions to Maxwell's equation in the case of a upper-hybrid resonance in the cold plasma model. We base our analysis in the transfer to the time domain of the recent results of B. Despr\'es, L.M. Imbert-G\'erard and R. Weder, J. Math. Pures Appl. {\bf 101} ( 2014) 623-659, where the singular solutions to Maxwell's equations in the frequency domain were constructed by means of a limiting absorption principle and a formula for the heating of the plasma in the limit of vanishing collision frequency was obtained. Currently there is considerable interest in these problems, in particular, because upper-hybrid resonances are a possible scenario for the heating of plasmas, and since they can be a model for the diagnostics involving wave scattering in plasmas.Comment: This published version has been edited to improve the presentation of the result

Astrophysics of Super-massive Black Hole Mergers

We present here an overview of recent work in the subject of astrophysical manifestations of super-massive black hole (SMBH) mergers. This is a field that has been traditionally driven by theoretical work, but in recent years has also generated a great deal of interest and excitement in the observational astronomy community. In particular, the electromagnetic (EM) counterparts to SMBH mergers provide the means to detect and characterize these highly energetic events at cosmological distances, even in the absence of a space-based gravitational-wave observatory. In addition to providing a mechanism for observing SMBH mergers, EM counterparts also give important information about the environments in which these remarkable events take place, thus teaching us about the mechanisms through which galaxies form and evolve symbiotically with their central black holes.Comment: Invited article for the focus issue on astrophysical black holes in Classical and Quantum Gravity, guest editors: D. Merritt and L. Rezzoll

Alfvén 'resonance' reconsidered: Exact equations for wave propagation across a cold inhomogeneous plasma

Previous discussions of Alfvén wave propagation across an inhomogeneous plasma predicted that shear Alfvén waves become singular (resonant) at the omega = k(z)v(A) layer and that there is a strong wave absorption at this layer giving localized ion heating. In this paper the three standard derivations of the Alfvén 'resonance' (incompressible magnetohydrodynamics, compressible magnetohydrodynamics, and two-fluid) are re-examined and shown to have errors and be mutually inconsistent. Exact two-fluid differential equations for waves propagating across a cold inhomogeneous plasma are derived; these show that waves in an ideal cold plasma do not become 'resonant' at the Alfvén layer so that there is no wave absorption or localized heating. These equations also show that the real 'shear' Alfvén wave differs in substance from both the ideal MHD and earlier two-fluid predictions and, in the low density, high field region away from the omega = k(z)v(A) layer, is actually a quasielectrostatic resonance cone mode. For omega much-lesser-than omega(ci) and k(y) = 0, the omega = k(z)v(A) layer turns out to be a cutoff (reflecting) layer for both the 'shear' and compressional modes (and not a resonance layer). For finite omega/omega(ci) and k(y) = 0 this layer becomes a region of wave inaccessibility. For omega much-lesser-than omega(ci) and finite k(y) there is strong coupling between shear and compressional modes, but still no resonance