Rotation Measurement and Control of Optically Trapped Particles
Akihiro Yamamoto and Ichirou Yamaguchi
Optical Engineering Laboratory, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama, 351-01 Japan
When a particle of isotropic shape is trapped by a convergent laser beam, it begins to rotate around itself. This self-rotation is caused by the torque resulting from total forces acting on the particle surface. We have developed a method to quickly and automatically measure the rotation rate from temporal variation of the light scattered from the particle. The rotation rate is derived from the period of the intensity variation. The rotation rate can be measured up to 3000rpm. The rotation rate that has been proportional to the trapping beam power is feedback controlled by a loop connecting the measured rotation rate and the trapping beam power.