Generating Bessel beams with broad depth-of-field by using phase-only acoustic holograms

Abstract

We report zero-th and high-order acoustic Bessel beams with broad depth-of-field generated using acoustic holograms. While the transverse field distribution of Bessel beams generated using traditional passive methods is correctly described by a Bessel function, these methods present a common drawback: the axial distribution of the field is not constant, as required for ideal Bessel beams. In this work, we experimentally, numerically and theoretically report acoustic truncated Bessel beams of flat-intensity along their axis in the ultrasound regime using phase-only holograms. In particular, the beams present a uniform field distribution showing an elongated focal length of about 40 wavelengths, while the transverse width of the beam remains smaller than 0.7 wavelengths. The proposed acoustic holograms were compared with 3D-printed fraxicons, a blazed version of axicons. The performance of both phase-only holograms and fraxicons is studied and we found that both lenses produce Bessel beams in a wide range of frequencies. In addition, high-order Bessel beam were generated. We report first order Bessel beams that show a clear phase dislocation along their axis and a vortex with single topological charge. The proposed method may have potential applications in ultrasonic imaging, biomedical ultrasound and particle manipulation applications using passive lenses.

Use of Dielectric Metasurfaces to Generate Deep‐Subwavelength Nondiffractive Bessel‐Like Beams with Arbitrary Trajectories and Ultralarge Deflection

“…And the nonhomogeneous intensities with multiple ripples along the trajectories are in accordance with the behavior of truncated Bessel functions of the beams. [ 38 ] Figure 5c,f explores the field profiles at the locations of the white dashed‐lines in Figure 5b,e and shows that the measured FWHMs are 1.31 and 1.05 µm, which are quite near the theoretical values of 1.29 and 1.08 µm, respectively. The field distributions of the array shown in Figure 5a–e indicate that the deflection of the beams in the array is small and indistinct relative to that of the aforementioned single accelerating Bessel‐like beam due to the beam's initial design parameters.…”

“…The intensity ripples along the trajectory are caused by the limited aperture of each annulus. [ 38 ] One high bright spot in Figure 2d,e corresponds to the ripple with the highest intensity. Other ripples are so densely distributed that they are not obviously shown.…”

Transversally travelling ultrasound for light guiding deep into scattering media

“…The direct translation of the method requires an axially extended uniform positive instantaneous pressure region and provides a difficult challenge. However, utilizing annular arrays with coaxial opening 48 and US Bessel beams 49 , an on-axis series of two-dimensional gradient refractive index medium lenses might be induced, that are potentially capable of light waveguiding or even relay imaging 27 . We suggest to investigate such arrangements further for possible in vivo applications with single-sided access.…”

Modern Types of Axicons: New Functions and Applications

“…The zero and high-order BB, also known as a nondiffracting beam (hereafter denoted as NDB), has several benefits, including preserving the size and shape of the central spot [ 9 , 10 , 11 ]. NDBs have been utilized in several applications, including laser machining [ 12 ], field depth extension [ 13 ], measuring multi-degree-of-freedom error motions [ 14 ], and 3D shape evaluation [ 15 , 16 ]. Vortex beams, specifically BBs, have recently attracted a lot of attention due to their unique properties in particle trapping [ 17 , 18 , 19 ], particle handling/rotation [ 20 , 21 ], and acoustic radiation force strategies in liquids [ 22 ].…”