Transmission characteristics of terahertz Bessel vortex beams through a multi-layered anisotropic magnetized plasma slab

The transmission of terahertz (THz) Bessel vortex beams through a multi-layered anisotropic magnetized plasma slab is investigated by using a hybrid method of cylindrical vector wave functions (CVWFs) and Fourier transform. On the basis of the electromagnetic boundary conditions on each interface, a cascade form of expansion coefficients of the reflected and transmitted fields is obtained. Taking a double Gaussian distribution of the plasma density as an example, the influences of the applied magnetic field, the incident angle and polarization mode of the incident beams on the magnitude, OAM mode and polarization of the transmitted beams are analyzed in detail. The results indicate that the applied magnetic field has a major effect upon the polarization state of the transmitted fields but not upon the transmitted OAM spectrum. The incident angle has a powerful influence upon both the amplitude profile and the OAM spectrum of the transmitted beam. Furthermore, for multiple coaxial vortex beams, an increase of the maximum value of the plasma density causes more remarkable distortion of both the profile and OAM spectrum of the transmitted beam. This research makes a stable foundation for the THz OAM multiplexing/demultiplexing technology in magnetized plasma environment.

Coupling of Upper Hybrid Surface Plasmon Modes in Magnetoplasma Waveguide Structure

We investigate the spectra of high-frequency electrostatic surface electron plasmon oscillations propagating normal to a dc-magnetic field. These oscillations are supported by two identical magnetoplasma slabs separated by a vacuum slab. Propagation characteristics of surface magnetoplasma oscillations and their coupling are studied by simultaneously solving the homogeneous system of equations obtained by matching the electrostatic fields at the interfaces together with the warm plasma dielectric function of upper hybrid waves. We demonstrate the existence of two propagating magnetoplasma electrostatic surface modes (backward and forward modes). The backward mode emerges at frequency ω=ω_uh=√(ω_pe^2+ω_ce^2 ), where ω_pe and ω_ce are the electron plasma frequency and the electron cyclotron frequency, respectivily, and the forward propagating mode emerges at a lower frequency ω=ω_uh-ω_pe. The forward and backward surface modes become coupled and form a single mode at upper hybrid resonance quasi-static value ω=ω_uh/√2. Keywords: Upper hybrid modes, Plasma slab waveguide, Coupled plasmon surface modes.

Self-modulation of fast radio bursts

ABSTRACT Fast radio bursts (FRBs) are extreme astrophysical phenomena entering the realm of non-linear optics, a field developed in laser physics. A classical non-linear effect is self-modulation. We examine the propagation of FRBs through the circumburst environment using the idealized setup of a monochromatic linearly polarized GHz wave propagating through a uniform plasma slab of density N at distance R from the source. We find that self-modulation occurs if the slab is located within a critical radius Rcrit ∼ 1017(N/102 cm−3)(L/1042 erg s−1) cm, where L is the isotropic equivalent of the FRB luminosity. Self-modulation breaks the burst into pancakes transverse to the radial direction. When R ≲ Rcrit, the transverse size of the pancakes is smaller than the Fresnel scale. The pancakes are strongly diffracted as the burst exits the slab, and interference between the pancakes produces a frequency modulation of the observed intensity with a sub-GHz bandwidth. When R ∼ Rcrit, the transverse size of the pancakes becomes comparable with the Fresnel scale, and the effect of diffraction is weaker. The observed intensity is modulated on a time-scale of 10 µm, which corresponds to the radial width of the pancakes. Our results suggest that self-modulation may cause the temporal and frequency structure observed in FRBs.