| Based on the radiation forces of laser beams,optical tweezers are capable of trapping microscopic particles and measuring micro-forces on the micro-nano scale by using optical traps.Among many technologies of manipulation,Optical tweezers have unique advantages: nanometer resolution on displacement and femtonewton resolution on force.This technology is widely applied in life sciences,the physics of colloidal systems and nanoscience fields.With scientific progress and technological innovation,traditional optical tweezers with Gaussian beam can’t meet the needs of researchers.Theoretical and experimental investigations demonstrate that,by using special laser beams,the performance of optical tweezers can be well improved and some new optical micromanipulation techniques can be realized.Singularities beam as a kind of special beam owning unique characteristic.Therefore,it is very important and significant to investigate the radiation forces of the focused singularities beams on particles.In this paper,taking Gaussian Schell-model(GSM)vortex beams,partially coherent circular edge dislocations beams,partially coherent Modified Bessel-Gaussian(MBG)beam and rectangular array vortex beams as research objects.The radiation force and the capture of four kinds of singularities beams on Rayleigh particles with different refractive index are analyzed,whose major contents are as follows:Based on the extended Huygens-Fresnel principle and Rayleigh scattering theory,propagations of the GSM vortex beams through a focusing optical system are formulated.The radiation force acting on Rayleigh dielectric sphere with different refractive indices produced by focused GSM vortex beams is investigated theoretically.Numerical results demonstrate that the focused GSM non-vortex beam can not trap the low index of refraction particles,but can capture the high index of refraction particles.The focused GSM vortex beam can be used to trap high index of refraction particles to a bright ring of the focal plane,and simultaneously capture low index of refraction particles to z-axis.The larger the topological charge is,the larger the value of the spatial correlation length is,the easier it is to trap two types of particles is.A focused partially coherent circular edge dislocations beam used to trap Rayleigh dielectric sphere with different refractive indices is studied.The dependence of radiation forces on the number of circular edge dislocations,the spatial correlation length,relative refractive index,and particle radius are analyzed and illustrated by numerical examples.It is shown that the focused partially coherent circular edge dislocations beam can be used to trap high index of refraction particles at focus and bright ring,and simultaneously to capture low index of refraction particles at dark ring.It is much easier to capture the high index of refraction particles at focus and the low index of refraction particles at dark ring as for the larger number of circular edge dislocations and the spatial correlation length,therefore it is necessary to optimally choose on number of circular edge dislocations and the spatial correlation length for obtaining an optimal optical guiding.The ranges of the radius for two types of particles stably captured also have been determined.Using the extended Huygens-Fresnel principle and Rayleigh scattering regime,the analytical expressions for the intensity and radiation forces of a focused partially coherent MBG beam have been derived and used to study the optical trapping effect of focused partially coherent MBG beams acting on dielectric sphere with different refractive indices.The results show that the focused partially coherent MBG beam with m = 0 can not capture the low index of refraction particles,but can trap the high index of refraction particles.The focused partially coherent MBG beam with the topological charge m ≥ 1 can trap high index of refraction particles to a ring on the focal plane,and simultaneously capture the low index of refraction particles to z-axis.With the topological charge increasing,the radiation force decreases while the transverse trapping range increases for low and high index of refraction particles.Besides,the larger the value of the spectral degree of coherence is,the easier the two types of particles are trapped by the focused partially coherent MBG beam is.Trapping stability is also analyzed.Based on coherent superposition and incoherent superposition mode,the analytical expressions for the intensity of rectangular array Gaussian Schell-model(RAGSM)vortex beams through a focusing optical system are derived.The optical trapping effect of RAGSM vortex beams acting on Rayleigh dielectric spheres is studied.The influence of superposition mode on capture stability and axial trapping range is analyzed.It is found that the coherent and incoherent superpositions RAGSM vortex beams can be used to trap multiple particles with rectangular array distribution at the same time in output plane,the beamlet at the center can capture the particles in the surrounding region by the two-dimensional(x-y)plane,and the other beamlets can trap the particles in the corresponding region in three dimensions.Furthermore,the axial capture range of the incoherent superposition RAGSM vortex beam to the particles is larger than that of the coherent superposition of the RAGSM vortex beam. |
