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Proceedings Paper

Investigation of the factors affecting the transverse force measurements of an optical trap: II
Author(s): Amanda Wright; Tiffany A. Wood; Mark Russell Dickinson; Helen F. Gleeson; Tom Mullin; Andrew Murray
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Paper Abstract

Many applications of laser tweezers rely on the accurate measurement of the transverse or axial trapping force. We have concentrated on the transverse trapping force and the most common method used to measure it, applying a viscous drag force. A trapped sphere was subjected to a viscous drag force via a Stokesian flow. The flow was achieved by oscillating the sample stage at a constant speed of 750 microns/second. A Zeiss oil-immersion (N.A. equals 1.3) objective was used to focus a 1064 nm Nd:YVO4 laser beam in order to trap 6 microns diameter polystyrene spheres suspended in distilled water. The minimum power needed to hold the particle in the trap at a particular viscous drag force was then measured. The influence of trap depth, oscillation amplitude used and particle concentration have been investigated, in particular the effects caused by the characteristics of the function used to create the oscillation. The minimum laser power needed to trap a sphere was found to increase with a rise in oscillation amplitude. The velocity profile through the fluid, the rotation of the trapped particle and the effect of interactions with other particles is considered when explaining these effects.

Paper Details

Date Published: 28 May 2002
PDF: 9 pages
Proc. SPIE 4622, Optical Diagnostics of Living Cells V, (28 May 2002); doi: 10.1117/12.468344
Show Author Affiliations
Amanda Wright, Univ. of Manchester (United Kingdom)
Tiffany A. Wood, Univ. of Manchester (United Kingdom)
Mark Russell Dickinson, Univ. of Manchester (United Kingdom)
Helen F. Gleeson, Univ. of Manchester (United Kingdom)
Tom Mullin, Univ. of Manchester (United Kingdom)
Andrew Murray, Univ. of Manchester (United Kingdom)

Published in SPIE Proceedings Vol. 4622:
Optical Diagnostics of Living Cells V
Robert C. Leif; Daniel L. Farkas; Robert C. Leif, Editor(s)

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