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Proceedings Paper

Structured back focal plane interferometry (S-BFPI)
Author(s): A. Upadhya; Y. Zheng; L. Li; W. M. Lee
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Paper Abstract

In optical micromanipulation, back focal plane interferometry (BFPI) has remained the most widely used method for tracking dielectric and metallic microparticles with nanometer resolution precision at speeds of up to few a MHz. Basic BFPI employs Gaussian beams which severely limits the detection range of the technique unless the focal parameters are tuned by increase the width of the beam, but this is usually concomitant with significant loss in detection sensitivity. A challenge in BFPI is to extend its linear range while maintaining this detection sensitivity along each axis. We constructed a system which utilizes a combination of structured beam shaping and structured detection (Annular Quadrant Detection), which we called Structured Back Focal Plane Interferometry (S-BFPI). A Gaussian beam is shaped by a spatial light modulator by imparting a conical wavefront, which increases the depth of focus while simultaneously maintaining the Gouy phase shift and hence the sensitivity of detection. In addition, an annular QPD is used for detection. Using S-BFPI, we were able to achieve a 200% axial range extension with only a 4.6% reduction in insensitivity, and a 167% lateral range extension with a 45% reduction in sensitivity. SBFPI can tailor its detection range and sensitivity over an intermediate range of displacement and sensitivity improvements at hand. We finally demonstrated its robustness against aberrations common to optical systems. S-BFPI presents itself as a flexible, tunable option for use as an optical measurement tool.

Paper Details

Date Published: 30 December 2019
PDF: 3 pages
Proc. SPIE 11202, Biophotonics Australasia 2019, 112021D (30 December 2019); doi: 10.1117/12.2539556
Show Author Affiliations
A. Upadhya, The Australian National Univ. (Australia)
Y. Zheng, The Australian National Univ. (Australia)
L. Li, Sun Yat-Sen Univ. (China)
W. M. Lee, The Australian National Univ. (Australia)

Published in SPIE Proceedings Vol. 11202:
Biophotonics Australasia 2019
Ewa M. Goldys; Brant C. Gibson, Editor(s)

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