Acoustic vortex beams in synthetic magnetic fields

Abstract

We analyze propagation of acoustic vortex beams in longitudinal synthetic magnetic fields. We show how to generate two field configurations using a fluid contained in circulating cylinders: a uniform synthetic magnetic field hosting Laguerre-Gauss modes, and an Aharonov-Bohm flux tube hosting Bessel beams. For non-paraxial beams we find qualitative differences from the well-studied case of electron vortex beams in magnetic fields, arising due to the vectorial nature of the acoustic wave's velocity field. In particular, the pressure and velocity components of the acoustic wave can be individually sensitive to the relative sign of the beam orbital angular momentum and the magnetic field. Our findings illustrate how analogies between optical, electron, and acoustic vortex beams can break down in the presence of external vector potentials. arXiv:1908.08278v1 [physics.class-ph]

An analytical approximation to measure the extinction cross-section using: Localized Waves

“…Also, considering the vector effect [24] in the extinction. Several interesting acoustic scattering problems as spin propagation [44], orbital angular momentum [45], vortex modes in synthetic fluids [46], evanescent Bessel waves [47] could be studied using LW. This method can suit to study experimentally new structured beams, such as carving beams recently reported [48].…”

Polarization singularities and Möbius strips in sound and water-surface waves

“…This work was motivated by recent strong interest in (i) polarization Möbius strips in 3D polarized optical fields [27][28][29][30][31][32][33][34][35][36] and (ii) vectorial spin properties of acoustic and water-surface waves [4][5][6][7][8][9][10][11][12]. We have shown that these research directions can be naturally coupled, and that polarization singularities, such as C-points and polarization Möbius strips, are ubiquitous for inhomogeneous (yet monochromatic) acoustic and water-surface waves.…”

“…where k = k/𝑘, k is the wavevector, 𝑘 = 𝜔/𝑐 is the wavenumber, 𝑐 = 1/ √ 𝜌𝛽 is the speed of sound, and 𝑃 0 = √︀ 𝜌/𝛽 𝑉 0 . Sound waves are longitudinal because V ‖ k, but still have a vector nature described by the velocity field V [4,[6][7][8][9][10]. In what follows, we will focus on the polarization properties of this vector wave field: the real velocity field 𝒱(r, 𝑡) at a given point r traces a polarization ellipse.…”

“…These are typically associated with classical electromagnetic/optical fields or quantum particles with spin [1][2][3]. Recently, it was noticed that sound waves in fluids or gases [4][5][6][7][8][9][10] as well as water-surface (e.g., gravity) waves [11,12] also possess inherent vector properties, and the notions of polarization and spin are naturally involved there. These properties are related to waveinduced motion of the medium particles in fluids and gases.…”

Acoustic spin and orbital angular momentum using evanescent Bessel beams

“…A complete review of the theoretical foundations for the acoustic and electromagnetic field theory has also been reported [12]. Applications in acoustic plasmon propagation in waveguides making analogies with electromagnetic fields [13], acoustic surface waves [14], acoustic radiation forces [15,16,17,18,19], enhanced manipulation in near fields [20], in fluids physics propagating vortex [21], in inhomogeneous media [22] using meta-surface waveguides have been demonstrated applications on spinrelated robust transport [23], and the importance to explore symmetry properties to enhanced acoustic propagation in the near field [24].…”