Generation of Bessel-Gaussian vortex beam by combining technology

Abstract

Bessel beam is an important member of the family of non-diffracting beams and has some unique properties which can be used in many areas, such as micro particle manipulating, material processing and optical communication. However, the source of Bessel beam generated by the existing methods can be used only in a short distance due to its low power. In this paper, according to the coherent combining technology, we propose a method to generate a second-order Bessel-Gaussian (BG) beam by loading discrete vortex phase on specific spatially distributed Gaussian beam array. The coherent combining technology can enhance the output power by increasing the number of beams and use the phase-locking technique to maintain the beam quality. The experimental scheme is described as follows. The expanded Gaussian beam is first split by an amplitude-based spatial light modulator, then the Gaussian beam array is incident on a phase-only spatial light modulator to load the discrete vortex phase, and finally the Gaussian beam array loaded with phase can synthesize BG beam in free space. Due to the diffraction effect of the sub-beams, the optical field distribution between the adjacent sub-beams which are loaded with phase differences, are superimposed. As a result, the optical field distribution of the approximate beam can be obtained by coherent synthesis in free space. After that, the degree of similarity between simulated results and theoretical data is analyzed by correlation coefficient, including the comparison of light intensity between experiment and simulation, and the power-in-the-bucket is used to evaluate beam quality. In addition, the topological charge of the synthesized BG beams is verified by the interference method. By studying the number of beams, the waist radius and the radius of the ring, we find some interesting results which are summarized as follows. Firstly, the closed arrangement of Gaussian beam arrays can improve the quality of the synthesized BG beam. Secondly, the smaller the phase difference between the sub-beams, the more easily the discontinuous piston phase approaches to the vortex phase. Therefore, increasing the number of sub-beams can significantly improve the beam quality of the synthesized BG beam and obtain a higher order synthetic BG beam. Finally, we define the parameter k to represent the tightness of a circular array of Gaussian beams. The present study shows that when the parameter k is close to 1, the best experimental results can be obtained. Therefore, the proposed method has important guidance in generating various vortex beams or enhancing the vortex beam power.

Acoustic Trapping: An Emerging Tool for Microfabrication Technology

“…In contrast, the deposition of microparticles in a nonsymmetrical spatial arrangement requires the generation of arbitrary and aperiodic acoustic pressure fields. To generate such nonsymmetrical acoustic pressure fields generally requires more complex devices using complicated arrangements of transducers or structures such as acoustic holograms, which give rise to a wide range of patterns, including Bessel-function acoustic pressure fields [40,74,75,77,[85][86][87][88] or arbitrary patterns. [41,[89][90][91][92][93][94][95] To this end, different types of acoustic trapping devices with more transducer elements, such as 1D, 2D, [40,77] or circularly arranged [74,75,[85][86][87] ultrasound transducer arrays, have been developed.…”

“…To generate such nonsymmetrical acoustic pressure fields generally requires more complex devices using complicated arrangements of transducers or structures such as acoustic holograms, which give rise to a wide range of patterns, including Bessel-function acoustic pressure fields [40,74,75,77,[85][86][87][88] or arbitrary patterns. [41,[89][90][91][92][93][94][95] To this end, different types of acoustic trapping devices with more transducer elements, such as 1D, 2D, [40,77] or circularly arranged [74,75,[85][86][87] ultrasound transducer arrays, have been developed. The additional modulation of the frequency, phase, amplitude, and pulse duration of the individual elements of the ultrasound transducer can be used to deposit microparticles in an arbitrary acoustic pressure field to generate nonsymmetrical patterns.…”

Optimization for coherent combined vortex fiber array with phase correction

“…As shown in Figure 1, N is the number of inner and outer ring sub-beam, l 0 is the target topological charge number , ω 01 and ω 02 are the inner and outer ring sub-beam beam waist radius, and R 1 , R 2 are the inner and outer ring array radius. The light field in the emission plane can be expressed as [13][14] :…”

Rotational speed measurement under misalignment conditions based on rotational Doppler effect

“…1(b). The target, paralleled with the array plane, rotates around the z-axis with rotational speed v. The discrete phase φ=nφm =2πnm/M is superimposed on each single beam in turn, where n is topological charge, φm is the angle between individual beams and x-axis, m is the sequence number of sub-beams, and M is the number of sub-beams [20] . The initial optical field distribution at z=0 m is represented in cylindrical coordinate system by Eq.…”