Subwavelength Acoustic Vortex Beams Using Self-Demodulation (original) (raw)
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Journal of Applied Physics, 2021
Here, we present a class of metamaterial-based acoustic vortex generators which are both geometrically simple and broadly tunable. The aperture overcomes the significant limitations of both active phasing systems and existing passive coded apertures. The metamaterial approach generates topologically diverse acoustic vortex waves motivated by recent advances in leaky wave antennas by wrapping the antenna back upon itself to produce an acoustic vortex wave antenna. We demonstrate both experimentally and analytically that this single analog structure is capable of creating multiple orthogonal orbital angular momentum modes using only a single transducer. The metamaterial design makes the aperture compact, with a diameter nearly equal to the excitation wavelength and can thus be easily integrated into high-density systems. Applications range from acoustic communications for high bit-rate multiplexing to biomedical devices such as microfluidic mixers.
Acoustic vortex beams in synthetic magnetic fields
Journal of Physics: Condensed Matter, 2019
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.
Generation of optical vortex dipole from superposition of two transversely scaled Gaussian beams
Applied optics, 2016
We propose a distinct concept on the generation of optical vortex through coupling between the amplitude and phase differences of the superposing beams. For the proof-of-concept demonstration, we propose a simple free-space optics recipe for the controlled synthesis of an optical beam with a vortex dipole by superposing two transversely scaled Gaussian beams. The experimental demonstration using a Sagnac interferometer introduces the desired amount of radial shear and linear phase difference between the two out-of-phase Gaussian beams to create a vortex pair of opposite topological charge in the superposed beam. Flexibility to tune their location and separation using the choice of direction of the linear phase difference and the amount of amplitude difference between the superposing beams has potential applications in optical tweezers and traps utilizing the local variation in angular momentum across the beam cross section.
Evanescent vortex: Optical subwavelength spanner
Applied Physics Letters, 2016
Conventional optical spanners based on free-space focused vortex beams are very difficult to manipulate subwavelength objects due to the diffraction limit, while optical subwavelength spanners are not explored. Evanescent wave is one potential tool to realize subwavelength trapping. By combining vortex with evanescent field, we find that the evanescent vortex can function as an optical subwavelength spanner. We investigate the factors that will affect the generation/function of this subwavelength spanner, including numerical aperture and topological charge. Further, by calculating the optical force and potential on the illuminated objects, we have demonstrated that the evanescent optical vortex field is able to trap 200 nm polystyrene spherical particles and to rotate them around the ring-shaped field at the same time, making it a subwavelength optical spanner. This mechanism can be used as a tool to study the behaviour of very small objects in physics and biology.
Pseudo Angular Momentum and Topological Charge Conservation for Nonlinear Acoustical Vortices
We study acoustical vortices (AVs) and their connection with optical vortices (OVs). We show that AVs and OVs have the same properties if the concept of pseudomomentum is used. Radiation stress and conservation of topological charge are obtained with the pseudomomentum rule. In a weak nonlinear regime, the conservation of pseudo angular momentum imposes a linear increase of the topological charge with the harmonic order. This last result is experimentally verified.
Note: A simple experimental arrangement to generate optical vortex beams
Review of Scientific Instruments, 2013
Effective quantum teleportation of an atomic state between two cavities with the cross-Kerr nonlinearity by interference of polarized photons J. Appl. Phys. 109, 103111 (2011) Transient interference implications on the subpicosecond laser damage of multidielectrics Appl. Phys. Lett. 97, 051112 (2010) Additional information on Rev. Sci. Instrum. Kumar, Das, and Boruah Rev. Sci. Instrum. 84, 026103 (2013) FIG. 2. The computed holograms corresponding to topological charge, (a) m = 0, (b) m = 1, and (c) m = 2, each printed over a circular area of the transparent sheet of diameter 1.7 cm.
Transmission of sound through a single vortex
The European Physical Journal B - Condensed Matter, 2003
We investigate experimentally the deformation of acoustic wavefronts after crossing of a single, isolated vortex in free space. The incident sound wavelength can be varied in a large domain. We study the wavefronts at variable distance after transmission through the vortex, when the wavelength and the vortex strength are varied. For small wavelength (λ a, the vortex core size) our results are in very good agreement with predictions and simulations based on geometrical acoustics principles. However, as the sound wavelength increases to value comparable with the vortex diameter, the deformation of the wavefronts show the development of scattering contributions, with characteristics in agreement with recent theoretical and numerical studies.
Generating and analyzing non-diffracting vector vortex beams
Laser Beam Shaping XIV, 2013
We experimentally generate non-diffracting vector vortex beams by using a Spatial Light Modulator (SLM) and an azimuthal birefringent plate (q-plate). The SLM generates scalar Bessel beams and the q-plate converts them to vector vortex beams. Both single order Bessel beam and superposition cases are studied. The polarization and the azimuthal modes of the generated beams are analyzed. The results of modal decompositions on polarization components are in good agreement with theory. We demonstrate that the generated beams have cylindrical polarization and carry polarization dependent Orbital Angular Momentum (OAM).
Cyclones and attractive streaming generated by acoustical vortices
2014
Acoustical and optical vortices have attracted large interest due to their ability in capturing and manipulating particles with the use of the radiation pressure. Here we show that acoustical vortices can also induce axial vortical flow reminiscent of cyclones whose topology can be controlled by adjusting the properties of the acoustical beam. In confined geometry, the phase singularity enables generating "attractive streaming" with a flow directed toward the transducer. This opens perspectives for contact-less vortical flow control.