Rotating Dynamics Analysis of Defective Homogeneous Sphere in Optical Tweezers

Abstract An optically levitated rotating sphere is an ultrasensitive torque sensor. In this article, a method was presented to apply a specially manufactured defective hollow homogeneous sphere as a stable rotor. The numerical relationship between the external torque and attitude of a suspended rotating defective homogeneous sphere captured by a circularly polarized laser was determined. The trap stiffness and dynamic process of different particles were comparted to determine the feature of an ideal rotor. Particles with larger hollow radii and centrifugal distances had greater potential in torque detection. The simulation of the trail path and the stabilization process of particles showed that rotating motion could effectively cool particles and neutralize the optical force brought by the imbalance of the rotor. A defective nanoparticle was droved to rotate at 3 kHz and the cooling effect was successfully observed. The analytical formulae and simulation results analyzed the gyroscope effect and provided selection criteria for rotors in optical tweezers for precise torque detection.