An efficient and inexpensive method that uses a glass plate mounted onto a motorized rotating stage as a beam-steering device for the generation of dynamic optical traps is reported. Force analysis reveals that there are drag and trapping forces imposed on the bead in the opposite directions, respectively, in a viscous medium. The trapped bead will be rotated following the beam's motion before it reaches the critical escape velocity when the drag force is equal to the optical trapping force. The equilibrium condition facilitates the experimental measurement of the drag force with potential extensions to the determination of the viscosity of the medium or the refractive index of the bead. The proposed technique can easily be integrated into conventional optical microscopic systems with minimum modifications.
© 2011 Chinese Optics Letters
(120.4820) Instrumentation, measurement, and metrology : Optical systems
(170.4520) Medical optics and biotechnology : Optical confinement and manipulation
(350.4855) Other areas of optics : Optical tweezers or optical manipulation
Xiaocong Yuan, Yuquan Zhang, Rui Cao, Xing Zhao, Jing Bu, and Siwei Zhu, "Dynamic steering beams for efficient force measurement in optical manipulation," Chin. Opt. Lett. 9, 031201- (2011)