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Proceedings Paper

Factors affecting the transverse force measurements of an optical trap: I
Author(s): Tiffany A. Wood; Amanda Wright; Helen F. Gleeson; Mark Dickenson; Tom Mullin; Andrew Murray
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Paper Abstract

The transverse force of an optical trap is usually measured by equating the trapping force to the viscous drag force applied to the trapped particle according to Stokes' Law. Under normal conditions, the viscous drag force on a trapped particle is proportional to the fluid velocity of the medium. In this paper we show that an increase of particle concentration within the medium affects force measurements. In order to trap the particle, 1064 nm light from a Nd:YVO4 laser was brought to a focus in a sample slide, of thickness around 380 microns, by using an inverted Zeiss microscope objective, with NA equals 1.3. The slide was filled with distilled water containing 6 micron diameter polystyrene spheres. Measurements were taken at a fluid velocity of 0.75 microns/sec, achieved by moving the sample stage with a piezo-electric transducer whilst a particle was held stationary in the trap. The laser power required to hold a sphere at different trap depths for various concentrations was measured. Significant weakening of the trap was found for concentrations >0.03% solids by weight, becoming weaker for higher trap depths. These results are explained in terms of aberrations, particle-particle interactions and distortion of the beam due to particle-light interactions.

Paper Details

Date Published: 28 March 2002
PDF: 7 pages
Proc. SPIE 4634, Methods for Ultrasensitive Detection II, (28 March 2002); doi: 10.1117/12.463827
Show Author Affiliations
Tiffany A. Wood, Univ. of Manchester (United Kingdom)
Amanda Wright, Univ. of Manchester (United Kingdom)
Helen F. Gleeson, Univ. of Manchester (United Kingdom)
Mark Dickenson, Univ. of Manchester (United Kingdom)
Tom Mullin, Univ. of Manchester (United Kingdom)
Andrew Murray, Univ. of Manchester (United Kingdom)


Published in SPIE Proceedings Vol. 4634:
Methods for Ultrasensitive Detection II
Charles W. Wilkerson, Editor(s)

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