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Proceedings Paper

A method of laser-induced microscopic torque measurement
Author(s): Yonghong Liu; Jinshan Shi; Yuyan Zhang
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Paper Abstract

It has been established that under certain conditions a tightly focused laser beam can trap microscopic particles in the size range from tens of nanometers to tens of micrometers. This technique is commonly referred to as optical tweezers and is widely used in many biological applications. The optical forces and torques applied by the trapping beam to the particle result from the transfer of momentum and angular momentum from the trapping beam to the particle. In recent years there has been an explosive development of interest in the measurement of forces and torques at the microscopic level, such as within living cells, as well as of the properties of fluids and suspensions on this scale, using optically trapped particles as probes. Here we present a novel method for a simple, accurate, simultaneous measurement of the rotation speed of an optical trapped birefringent particle, and the optical torque acting on it, by measuring the change in angular momentum of the light from passing through the particle. This method does not depend on the size or shape of the particle or the laser beam geometry, nor does it depend on the properties of the surrounding medium, and provides a mean to accurately measure the viscosity of interest on a microscopic scale.

Paper Details

Date Published: 13 October 2006
PDF: 6 pages
Proc. SPIE 6280, Third International Symposium on Precision Mechanical Measurements, 62803V (13 October 2006); doi: 10.1117/12.716363
Show Author Affiliations
Yonghong Liu, Yanshan Univ. (China)
Jinshan Shi, Yanshan Univ. (China)
Yuyan Zhang, Yanshan Univ. (China)

Published in SPIE Proceedings Vol. 6280:
Third International Symposium on Precision Mechanical Measurements
Kuang-Chao Fan; Wei Gao; Xiaofen Yu; Wenhao Huang; Penghao Hu, Editor(s)

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