Research On Optical Tweezers Based On Spatial Mode Light Field

Optical tweezer,as an important hub for the study of interdisciplinary problems,has now become one of the indispensable tools in the fields of single molecule biophysics,cell biology,microchemistry,statistical physics,and laser cooling and trapping atoms.Multi-trap optical tweezers have a wide range of applications in many studies such as grasping large or complex samples and measuring the mechanical properties of samples.Diverse optical characteristics and beam profile make multi-traps optical tweezers possible.The optical tweezers based on vortex beams show remarkable flexibility in manipulating particles,providing a new degree of freedom for particle manipulation.A convenient way to construct multi-singularity vortex beams is the interference superposition of fundamental spatial modes carrying orbital angular momentum,which is also one of the schemes for constructing multi-trap optical tweezers.Currently,optical tweezers based on the different kinds of superposed Laguerre-Gaussian(LG)modes have been studied,such as bottle beams generated by superimposing different Laguerre-Gaussian mode beams with radial indices,and a focus hybrid vector beam produced by superposition of two orthogonal LaguerreGaussian beams with different orbital angular momentum(OAM)quantum numbers.Nonetheless,optical trapping characters of Laguerre-Gaussian composite vortex beams superposed directly by Laguerre-Gaussian modes with different orbital angular momentum quantum numbers have not been explored.The new vortices generated by multi-singularity vortex beams provide a new idea for constructing multi-trap optical tweezers.Here,a composite vortex beam based on Lagurerre-Gaussian mode is proposed.Its light field pattern and phase distribution are analyzed.A scheme is designed and realized in the experiment.The scheme is based on a single Spatial Light Modulator(SLM),and the experimental results show that the required composite vortex beam can be constructed relatively well.Then,the radiation forces of Laguerre-Gaussian composite vortex beams exerting on a Rayleigh dielectric particle are investigated.Our results show that the multi-trap optical tweezers can be produced by the LaguerreGaussian composite vortex beams,which can trap the particles with both high and low refractive indices in the focus plane at multiple positions.Moreover,by changing the orbital angular momentum quantum numbers and energy ratios of the Laguerre-Gaussian modes participated in the superposition,the quantities of the optical traps and the distances between multiple traps can be conveniently adjusted.Our beams can be generated by several methods,which provides more convenience for the creation of multiple optical traps.The results presented in this work are potential in optical micromanipulation,extended assembly,transportation and sorting technologies,as well as other applications in biology and chemistry.