Research On The Controllable Optical Rotation Technology Of Mesoscopic Particles

As a new non-contact and nondestructive optical micromanipulation technology,optical rotation technology can realize rotation manipulation of micrometer and sub-micrometer particles.It has a good application prospect in nanotechnology and biotechnology.It is widely used in micro mechanical motors,stable observation and manipulation of biological molecules and the viscosity measurement etc.In this paper,the experimental system is designed and built by using the dual-beam misalignment method.And we designed a PDMS chip,which is used to analyze the influence on particles rotation of the different parameters such as transverse offset distance,optical waist distance and laser power.We achieved the controllability of mesoscopic particles rotation.Firstly,the paper introduces the basic concepts of the optical rotation,and details the generation and development of the spin angular momentum transfer method,orbital angular momentum transfer method and linear momentum transfer method of optical rotation.This paper mainly introduces the research status of the dual-beam misalignment method,analyzes the advantages and disadvantages of different methods,and briefly describes the application prospect of the dual-beam misalignment method.Secondly,the basic concept of light pressure is introduced.It is shown that the particles will be affected by the gradient force and the scattering force in the optical trap.The optical force acting on the particle is analyzed by the ray model and simulated on the different condition,including different transverse offset distance,axial offset distance and optical waist distance.The rotation trajectory of the particles is simulated by analyzing the force acting on the particles.Thirdly,a set of experimental system for controllable optical rotation of mesoscopic particles was designed and built,based on the dual-beam misalignment method.Optical trap chip,as the core components of the system,is introduced in detail.The chip consists of two parts: sample channels and fiber channels,which is mainly used for particle capture and the movement of fiber,so as to realize the controllable optical rotation of particles.By adjusting the displacement stage,the displacement stage applies a pressure to the PDMS molded fiber channels causing elastic deformation of the chip,which in turn pushes the fiber away,so the transverse offset distance of the two fibers can be changed,and the controllable operation of the particle rotation can be realized.By the calibration,the minimum moving distance of optical fiber is 0.3μm,and it has high stability.Finally,we research the controllability of optical rotation of single-particle and multi-particle,which is formed by 10μm polystyrene particles.By comparing with the simulation results,the experimental results show that the trajectory perimeter and frequency of the rotation of single particles can be changed by changing the transverse offset distance,laser power and optical waist distance.For multi-particle array,the experimental results show an increasing of the rotation perimeter and decreasing of rotation frequency with increasing the transverse offset.The threshold values of transverse offset required to initiate rotation was found to be different for different number particle arrays.For multi-particle assembly,the trajectory perimeter increased,but the frequency decreased when transverse offset distance increased.Compared with multi-particle array,higher values of transverse offset is required to initiate rotation for multi-particle assembly.