Motion Detection And Cooling Of A Large-Sized Xicrosphere In Dual-Beam Optical Trap In Vacuum

As a noval optical technology,optical tweezers(OT)suspends,measures,and manipulates particles in the range of tens of nanometers to tens of micrometers by the radiation pressure of light.OT in vacuum have been widely used in the fields such as sensing with ultra-high precision and basic physics exploration,owing to its advantages of non-invasive suspension of neutral particles,isolation of thermal noise and high spatio-temporal resolution resolution.The detection and controlling of the centroid motion of a microsphere by dual-beam optical trap is one of the mainstream research schemes in OT in vacuum.In order to give full play to the unique advantages of this scheme in fileds such as measurement of ultra-weak acceleration,a series of problems including the precise detection and efficient cooling of microsphere motion need to be solved.To sovle them,the work of this paper includes:1)A scheme based on variable iris is proposed to decoupling the detection of the triaxial displacement of particle centroid:The far-filed intensity distribution of the laser scattered by a microsphere was numerically simulated.Then the relation between light intensity distribution and microsphere displacement was discovered and and the experimental device for the verification of decoupling was also built.Both simulation and experiment show that the scheme can reduce the coefficient of coupling by at least 22 dB,and the problem of detection coupling has been preliminarily solved.2)An in-suit scheme based on the observation of displacement spectrum for revolution suppression and alignment of dual-beam is proposed:The characteristics of revolution such as amplitude and frequency under different gas pressures and different radial distances between two beam focuses were studied with electromagnetic simulation and experiment under low pressure.Both simulation and experiment show that the radial distances of two beam focuses can be declined within 0.1 ?m,and the problem of disturblance caused by revolution in the process of cooling suppression is basically solved.3)A set of experimental platform of dual-beam optical trap aimed at the measurement and manipulation of a particle was constructed.The platform increases the maximum diameter of the microsphere in the existing research of dual-beam optical trap from 3 ?m to 10 ?m,which improves the theoretical value of acceleration measurement sensitivity.The detection sensitivity 0.2 pm/(?)of the particle displacement has been achieved by the D-shape mirror scheme and the modeling and optimization in noise transfer chain.Then in a high vacuum environment of pressure 2.7 × 10-5 mBar,the triaxial motion equivalent temperatures are cooled from room temperature to 22.6 mK,2.5 mK and 11.2 mK,respectively,by the differential cooling scheme and the analysis and optimization of the cooling model considering noise and hysteresis.Over all,three works including detection decoupling,revolution suppression,and cooling has been carried out for the measurement and manipulation of microsphere motion.This article rather comprehensively explored the scheme of suspending a large-sized microsphere in vacuum in OT.The research technical of the measurement has promoted the engineering practice of the OT in vacuum,and enhanced its potential in high-precision inertial navigation,geological survey and other measurement applications.