Study On The Dynamic Optical Trapping Based On The Light Field Modulation Of Multifocal Spots

Optical trapping,also known as optical tweezers,has been widely studied for its ability to capture,manipulate,and observe particles with high precision and non-destructiveness.Optical trapping has played an important role in biochemistry,medical science,physics research and many other fields.Multifocal light field modulation has been paid much attention by many researchers due to its ability of high efficiency,multi-position and parallel processing,and has been applied in many domains.In recent years,the research of optical trapping with multifocal light field has become a trend due to the superiorities of multifocal light field modulation,such as parallel trapping multi-particles and manipulating every single particle respectively.In order to achieve stable and accurate optical trapping,the key is to design the generation of multifocal light field to form array spots whose energy distribution of focal field is smooth,the focus position is accurate,the diffraction efficiency is high and every focus can be controlled respectively.Based on this purpose,we demonstrate many studies about multifocal array light field in this paper.The details are as follows:1.We demonstrate a non-iterative method using annular subzone phases(ASPs)that are composed of many annular subareas in which phase-only distributions with different 3D displacements are filled.The dynamic 3D multifocal spots with controllable position of each focal spot in the focal volume of the objective are created using the ASPs.2.A type of scalable self-imaging capable of variable magnification or minification of periodic objects is demonstrated in the focal plane of a lens illuminated by a point source.The theory and the experimental results show that the self-imaging phenomenon can also be realized in the focal plane of a lens regardless of whether the distances satisfy the lens formula or not.The particular property of this scalable self-imaging effect is that the images in the focal plane can be controlled with different scaling factors only when the distances between the point source and the periodic object satisfy a certain condition.3.A simple and effective approach is proposed for transforming a conventional Talbot array illuminator(TAI)with multilevel phase steps into a binary-phase TAI(BP-TAI)through detour phase encoding.The BP-TAI is a binary(O,?)phase-only diffractive optical element,which can be utilized to generate a large-scale focal spots array with a high compression ratio.4.A new paradigm is proposed for generating the perfect optical vortex(POV)with controlled structure and orbital angular momentum(OAM)distribution in the focal region of tightly focused systems.The efficiency of the proposed technique is demonstrated with the experiment of the dynamic manipulation of small particles.