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Proceedings Paper

Mathematical model of a DIC position sensing system within an optical trap
Author(s): Kurt D. Wulff; Daniel G. Cole; Robert L. Clark
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Paper Abstract

The quantitative study of displacements and forces of motor proteins and processes that occur at the microscopic level and below require a high level of sensitivity. For optical traps, two techniques for position sensing have been accepted and used quite extensively: quadrant photodiodes and an interferometric position sensing technique based on DIC imaging. While quadrant photodiodes have been studied in depth and mathematically characterized, a mathematical characterization of the interferometric position sensor has not been presented to the authors' knowledge. The interferometric position sensing method works off of the DIC imaging capabilities of a microscope. Circularly polarized light is sent into the microscope and the Wollaston prism used for DIC imaging splits the beam into its orthogonal components, displacing them by a set distance determined by the user. The distance between the axes of the beams is set so the beams overlap at the specimen plane and effectively share the trapped microsphere. A second prism then recombines the light beams and the exiting laser light's polarization is measured and related to position. In this paper we outline the mathematical characterization of a microsphere suspended in an optical trap using a DIC position sensing method. The sensitivity of this mathematical model is then compared to the QPD model. The mathematical model of a microsphere in an optical trap can serve as a calibration curve for an experimental setup.

Paper Details

Date Published: 26 August 2005
PDF: 8 pages
Proc. SPIE 5930, Optical Trapping and Optical Micromanipulation II, 593021 (26 August 2005); doi: 10.1117/12.616709
Show Author Affiliations
Kurt D. Wulff, Duke Univ. (United States)
Daniel G. Cole, Duke Univ. (United States)
Robert L. Clark, Duke Univ. (United States)

Published in SPIE Proceedings Vol. 5930:
Optical Trapping and Optical Micromanipulation II
Kishan Dholakia; Gabriel C. Spalding, Editor(s)

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