Characterization of phased array-steered acoustic vortex beams (original) (raw)
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Hybrid generation and analysis of vector vortex beams
Applied optics, 2017
A method is described for generating optical vector vortex beams carrying superpositions of orbital angular momentum states by using a tandem application of a spatial light modulator with a vortex retarder. The vortex component has a spatially inhomogeneous phase front that can carry orbital angular momentum, and the vector nature is a spatially inhomogeneous state of polarization in the laser beam profile. The vector vortex beams are characterized experimentally by imaging the beams at points across the focal plane in an astigmatic system using a tilted lens. Mathematical analysis of the Gouy phase shows good agreement with the phase structure obtained in the experimental images. The polarization structure of the vector beam and the orbital angular momentum of the vortex beam are shown to be preserved.
Subwavelength Acoustic Vortex Beams Using Self-Demodulation
Physical Review Applied
Acoustic vortices with subwavelength dimensions and tunable topological charge are theoretically and experimentally synthesized at distances far beyond the Rayleigh diffraction length of the source, using self-demodulation. A dual helical acoustic source is used to generate two primary confocal vortex beams at different frequencies and different topological charges. As a consequence of the conservation of angular momentum during nonlinear wave mixing, a self-demodulated vortex beam at the difference frequency emerges, keeping the spatial features of the primary vortex beams and a topological charge that is the difference of their topological charges. We report subdiffractive vortices the characteristic size of which is 18 times smaller than its wavelength at a distance 2.8 times the Rayleigh diffraction length. The generation and focusing of subwavelength vortices paves the way for long-range communication, biomedical, and wave-matter interaction applications.
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.
Propagation of vector vortex beams through a turbulent atmosphere
Optics Express, 2009
Name: Cheng, Wen University of Dayton Advisor: Dr. Qiwen Zhan This thesis study and compare the propagation properties of both scalar and vector vortex beams through turbulent atmosphere. The irradiance pattern, degree of polarization, and scintillation index of radially polarized beam are computed for different propagation distance into an atmosphere with weak and strong turbulence. Corresponding properties of a fundamental Gaussian beam, a scalar vortex beam with topological charge of +1 propagating through an atmosphere under the same turbulence condition are calculated for comparison. The results demonstrate that the existence of the vectorial vortex can be identified with longer propagation distance than the scalar vortex even with disappearing characteristic vortex structure in the irradiance images. This indicates the potential advantages of using vector vortex to mitigate atmospheric effects and enable a more robust free space communication channel with longer link distance. v ACKNOWLEDGEMENTS I would like to give my special thanks to Dr. Qiwen Zhan, my advisor, for providing great help in my thesis study. His patient and critical guidance help me solve problems and eventually lead the study to a positive conclusion.
FOCUS SHAPING OF CYLINDRICALLY POLARIZED VORTEX BEAMS BY A LINEAR AXICON
Electronic Journal of University of Aden for Basic and Applied Sciences, 2021
Focus shaping of cylindrically polarized vortex beams (CPVBs) by linear axicon is studied theoretically. Vector diffraction theory has been used to derive the expressions of the light field in the focal region. It is shown that a different intensity distribution in the focal region can be obtained by adjusting the topological charge, the polarization rotation angle and the numerical aperture maximal angle. A focal spot, a dark channel and a flat-topped shapes are formed by choosing proper values of parameters. A controllable polarization state of dark channel is obtained. The different focal region shapes may find wide applications such as material processing and optical tweezers.
A Simulation Study of the Beam Steering Characteristics for Linear Phased Arrays
1999
Ultrasonic beam steering characteristics for linear phased array transducers are simulated numerically by visualizing the full-field acoustic pressure field of the waves radiated from a linear phased array transducer. The influences of various transducer parameters on the beam steering properties are studied, including number of elements, inter-element spacing, element size, frequency of the transducer and the steering angle. In addition, the effects of these parameters on the near field characteristics are investigated by analyzing the acoustic pressure profile in the steering direction. The simulation results agree well with the analytical solutions which are valid only in the far field. A suggested scheme for optimal transducer design is presented.
On the backreaction of acoustic radiation for distributed two‐dimensional vortex structures
Physics of fluids, 1991
Acoustic radiation is calculated by the special hypocycloid-type vortices given by exact solutions of 2-D hydrodynamic equations, the Kirchhoff elliptic vortex being a particular case. Energy and angular momentum balance equations with fluxes due to outgoing waves are used to calculate, in adiabatic approximation, 'the evolution of parameters governing vorticity distribution. A possible implementation of the same technique to 3-D vortex filaments is briefly discussed.
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.
Microwave vortex beam launcher design
IET Microwaves, Antennas & Propagation
A novel design for a vectorial vortex beam launcher in the microwave regime is devised. The beam is formed by launching a single guided transverse electric (TE) mode of a metallic circular waveguide into free-space. Excitation is achieved by the mean of an inserted coaxial loop antenna. Modal expansion coefficients are computed, and the resulting electric and magnetic fields are determined. The effect of the antenna location inside the waveguide on its effective input impedance is modelled using transmission-line relations and location for optimal matching is established. The analytical results are confirmed using multi-level fast multipole method full-wave simulations.
Propagation of scalar and vector vortex beams through turbulent atmosphere
Atmospheric Propagation of Electromagnetic Waves III, 2009
In this paper, we study and compare the propagation properties of both scalar and vector vortex beams through turbulent atmosphere. The atmosphere turbulence effect is simulated with von Kármán power spectrum model using index of refraction structure parameter, C n 2 , values ranging from 10 -14 m -2/3 to 10 -12 m -2/3 . For different propagation distances, the irradiance pattern and the scintillation index are computed for a fundamental Gaussian beam, a scalar vortex with topological charge of +1 and a radially polarized beam under the same turbulence condition. The results demonstrate the advantages of using vector vortex to mitigate atmospheric effects. In addition, it is found by analyzing the polarization pattern of the transmitted vector vortex beams, that they may find applications in free space communications and remote sensing.