Measurement of rotated Janus particle’s position and orientation in the optical trap  

作　　者：Xiaoqing Gao Yulu Chen Hongbin Li Chunguang Hu 

机构地区：[1]State Key Laboratory of Precision Measurement Technology and Instruments,School of Precision Instrument and Opto-Electronics Engineering,Tianjin University,Tianjin 300072,China [2]Department of Chemistry,University of British Columbia,Vancouver,British Columbia V6T 1Z1,Canada

出　　处：《Nanotechnology and Precision Engineering》2024年第4期1-7,共7页纳米技术与精密工程(英文)

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.52075383 and 61927808);the National Key Research and Development Program of China(Grant No.2022YFF0605501).

摘　　要：Optical tweezers are precise tools for translating and rotating micrometer-sized particles and are used widely in biology and physics.In a linearly polarized optical trap,Janus particles comprising two hemispheres with different refractive indexes can be rotated about the beam axis following the polarization direction.In previous research,the position and orientation of a Janus particle relative to the polarization direction were simulated using the T-matrix method,whereas this paper is focused on accurate experimental measurements.The position and orientation of a Janus particle are extracted by image processing,and the polarization direction is controlled by a motor-driven half-wave plate(HWP).The particle’s orientation and the polarization direction are related via the HWP’s rotation angle.However,rotating the HWP not only rotates the polarization direction but also causes the trap center to fluctuate positionally because of the inevitable misalignment between the HWP’s rotation axis and the optical axis.Both the trap center and the polarization direction affect the particle’s position,but the influence of the former is removed with the aid of a homogeneous microsphere.The experimental results show that the Janus particle rotates following the polarization direction to keep the interface between its two hemispheres always parallel to the polarization direction.Also,the particle’s centroid moves in a circular orbit around the trap center to hold the trap center in the hemisphere with the higher refractive index.The experimental results agree with the previous simulation results and are of use for future applications.

关 键 词：Optical tweezers Janus particle ROTATION CALIBRATION 

分 类 号：O43[机械工程—光学工程]