The Numerical Simulation Investigation On The Stability Of Microspheres In A Dual Beam Light Trap

The microsphere in the dual-beam light trap is subjected to the capture of Gaussian lights and exhibits a suspended state.This trapped microsphere's Brownian motion weaken its position stability in the trap.Therefore,studying the position stability of the optical microsphere is of great significance to improve the measurement accuracy of the optical accelerometer.Based on the theoretical basis of the microsphere,the limited Brownian motion of the microspheres and the principle of the microsphere cooling method are studied,creatively.The numerical simulation of the particle's dynamics within the feedback cooling is carried out.And those analysis provides useful theoretical basis to the experiments.The basic concepts and applications of optical trapping and the Brownian motion of microspheres in optical traps are introduced briefly.In order to improve the position stability of microspheres,the focus of this paper is the cooling method of constrained microspheres in optical traps.Considering about the experiment mechanism,the cooling method can be divided into feedback cooling,optical microcavity and the gyro effect cooling.Among them,the feedback cooling method is divided into active feedback cooling and parameter feedback cooling.The principle of the feedback cooling method is to adjust the optical power of the captured light through the feedback of the real-time position signal,so as to achieve the best light distribution within a oscillation period and improve the position stability of the microsphere.The velocity iteration algorithm and position iteration algorithm based on Monte-Carlo method were used to simulate the motion equations of the microspheres in the optical trap.The effects of parameters such as radius r,trap stiffness k_trap,and fluid viscosity?on the position stability of SiO2 microspheres were analyzed by numerical simulation.In the air,when the radius of the microspheres is larger,the position stability of the trapped sphere is higher,and the greater trap stiffness results in a more stable microsphere;In the lean gas,when the viscosity of the gas is higher,the greater the stability of the position of the microspheres can be achieved.Via The numerical simulation of the motion equations of the microspheres under the two feedback cooling methods is as follows:if the other parameters are not changed,when the system pressure is 500 Pa,the SiO₂ microspheres with a radius of 5?m will be detached from the light trap.When the active feedback cooling coefficient is 1000,the stability of the microsphere in 400 Pa is much higher than that at a pressure of 1000 Pa without feedback.Under the parameter setting of parameter feedback cooling,when the pressure is lower than 400Pa,the microspheres with a radius of 70nm will be separated from the light trap.After the cooling feedback term is added,the microspheres can be stably captured in the optical trap,and the position stability of the microspheres increases with the feedback term.In addition,when analyzing the simulation results of the parametric feedback cooling method,it is found that at certain parameters,the microsphere's position power spectrum has a peak at a higher frequency in addition to the peak at the eigenfrequency.