Shubo Cheng, Tian Xia, Mengsi Liu, Yuanyuan Jin, Geng Zhang, Yan Xiong, Shaohua Tao
A new kind of beam, i.e., power-exponent helico-conical (PEHC) optical beams, has been proposed in this paper. The proposed beams possess a variety of interesting properties different from optical vortex beams. The intensities of the proposed optical beams at the focal plane are analyzed theoretically and experimentally. The far field mappings are also theoretically analyzed. The results demonstrate that the proposed beams have the ring-broken openings which can be adjusted by modifying the exponent n. The proposed beams can be useful for the extension applications of helico-conical optical beams, especially for optical trapping, guiding, and sorting.
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Zhirong Liu, Xun Wang, Kelin Huang
Propagation characteristics and optical forces exerted upon a Rayleigh dielectric sphere for a novel controllable dark-hollow beam (CDHB) are analyzed theoretically and illustrated numerically. In view of the unique focusing characteristics that a sharp, peak-centered, and adjustable configuration would be produced in the focal region, a tightly focused CDHB could be exploited to trap and manipulate particles with high-refractive index in the focal vicinity. Furthermore, it is significant that the CDHB tweezers’ trapping efficiency and optical trap stiffness could be finely controlled by adjusting either the targeted beam’s order or the central dark size controlling parameter. Finally, the trapping stability conditions are analyzed. The results obtained here are of interest and importance in optical manipulations and investigations for a CDHB.
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Shubo Cheng, Tian Xia, Mengsi Liu, Shan Xu, Shufang Gao, Geng Zhang, Shaohua Tao
The beams with phase gradients along the line trajectory, i.e., with the momentum flux transverse to the optical axis were generated with the beam shaping method and applied for optical manipulations in this paper. The phase distributions of the reconstructed beam in the focal plane of the objective and the moving velocity of the trapped microparticles were experimentally investigated. The experimental results showed that the moving velocity of the trapped microparticles is linearly dependent on the phase gradient possessed by the reconstructed beam. Furthermore, a generated curve beam was used to transport microparticles quickly and automatically along the curved route to avoid an obstacle. The generation method of the beams with phase gradients is simple. The beams would have potential applications in the fields such as optical trapping and optical sorting.
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Xingyu Chen, Jingli Zhuang, Xi Peng, Dongdong Li, Liping Zhang, Fang Zhao, Dongmei Deng
Here we investigate the propagation properties of spatiotemporal autofocused chirped Pearcey Pearcey Gaussian (PePeG) wavepackets by solving (3 + 1) D Schrdinger equation in a quadratic index medium. When the spatial distribution factor p and the temporal distribution factor f are the same, PePeG wavepackets can simultaneously autofocus in spatial and temporal domain and the peak intensity at the focus is more 28 times than that at the initial plane. With the increase of distribution factor p, the scope of the radius of trapped particles decreases.
DOI
Reuven Gordon
Nanoaperture optical tweezers extend the range of optical tweezers to dielectric particles below 50 nm in size. This allows for optical trapping of proteins, DNA fragments and other biomolecules, as well as small viruses. With this label-free, tether-free approach proteins have been trapped, sized and their conformational changes observed in real-time. The molecular weight of proteins in the nanoaperture trap was determined from their Brownian motion statistics. This is useful for analysis of heterogeneous solutions: since this is a single molecule technique, it can be operated in “dirty” solutions with minimal sample preparation. The acoustic modes of proteins, DNA fragments and other trapped nanoparticles can be measured using a nanoaperture optical tweezer with two lasers creating a GHz to THz beat frequency. Interactions between proteins and DNA, small molecules (i.e., binding) and other proteins have also been demonstrated. This single molecule technique allows for measuring the dissociation constants of small molecules binding to proteins, both at equilibrium and at the single molecule level. For DNA fragments in the trap, it has been shown that the protein p53 can suppress unzipping and mutant p53 is ineffective to do so. This is promising for the discovery of drugs that effectively restore the function to p53. Integration of nanoapertures on the ends of fibers allows for translocation of the trapped object and may function as an optical “nanopipette” for microwell single molecule protein sampling. There is also potential to combine nanoapertures with nanopore translocation studies as well as fluorescence correlation microscopy studies and several researchers are already pursuing these areas of research.
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Bin Tang, Kai Chen, Li Huang, Xin Zhou, Xianzhong Lang
Optical trapping and manipulating of micro particles have attracted extensive interests due to the advantages of being noncontact and noninvasive. In this work, the field distribution of Whittaker-Gaussian (WG) beams propagating through a lens and the radiation force acting on the Rayleigh particle are investigated numerically and theoretically. The results show that the WG beams can trap the particles with both high and low index of refractive near the focus. The influences of optical parameters on the radiation forces are analyzed in detail. Furthermore, the conditions for trapping stability are also discussed.
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Naomichi Yokoi, Yoshihisa Aizu
Most of optical manipulation techniques proposed so far depend on carefully fabricated setups and samples. Similar conditions can be fixed in laboratories; however, it is still challenging to manipulate nanoparticles when the environment is not well controlled and is unknown in advance. Nonetheless, coherent light scattered by rough object generates a speckle pattern which consists of random interference speckle grains with well-defined statistical properties. In the present study, we numerically investigate the motion of a Brownian particle suspended in water under the illumination of a speckle pattern. Particle-captured time and size of particle-captured area are quantitatively estimated in relation to an optical force and a speckle diameter to confirm the feasibility of the present method for performing optical manipulation tasks such as trapping and guiding.
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ZhengJun Li, ZhenSen Wu, Tan Qu, HaiYing Li, Lu Bai, Lei Gong
Based on orthogonality of associated Legendre functions and trigonometric functions, the radiation torque exerted on a uniaxial anisotropic sphere located in a linearly and circularly polarized Gaussian beam with arbitrary propagation direction is obtained. The radiation torque exerted on a uniaxial anisotropic sphere with different permittivity and permeability tensor elements illuminated by a linearly polarized Gaussian beam is calculated. The effects of the position of beam center, incident angle, polarization angle of the Gaussian beam, absorption, anisotropy ratio and size parameter on the three components of the radiation torque are numerically discussed in detail. The incident Gaussian beam can be a linear or a circular polarization. Some comparisons between these characteristics and those on an isotropic sphere are given.
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I.О. Kovaleva, O.B. Kovalev
The results of the numerical analysis of heat- and mass-transfer processes at powder particles' motion in a gas flow and laser beam by light-propulsion force during the laser cladding and direct material deposition are presented. Under consideration were the stainless steel particles, the radiation power range of the CO2 laser were 1000, 3000 and 5000 W. Finally, the particles of 45 μm in diameter reach the maximum velocity of about 80, 220, 280 m/s. It is shown that as particles are heated by the laser up to the temperature approaching the boiling point, the particles' velocity in the light field by the vapor recoil pressure may increase significantly. The radius of the particles slightly varies due to the evaporation; the losses in the clad material mass are negligibly small. Comparisons of numerical results with known experimental data on light-propulsion acceleration of single particles (aluminum, aluminum oxide and graphite) under the influence of pulse laser radiation are also presented. Particle acceleration resulting from the laser evaporation depends on the particle diameter, powder material properties, focusing degree and attenuation laser beam intensity by the direction of its propagation.
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