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Proceedings Paper

Polarization modulation of an optical trap's spring constant
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Paper Abstract

Using a Fresnel zone plate, we demonstrate optical trapping with a larger numerical aperture than is commonly available with commercial objective lenses. The zone plate is fabricated onto the inner wall of the fluidic cell and, consequently, focusing is free from on axis aberrations due to an absence of dielectric interfaces. Using zone plates with extremely large focusing angles, we observe an enhanced ellipticity in the trapping volume. For a zone plate with a numerical aperture of 0.986nwater (1.308), we observe a trapping stiffness that is more than four times stiffer perpendicular to the polarization than parallel to the polarization. By rotating the incident linear polarization state, the trapping stiffness along a given direction can be modulated by a factor of four. The ellipticity in the focal volume is due to the presence of an axial field component whose magnitude is proportional to the sine of the focusing angle of the lens.

Paper Details

Date Published: 29 August 2008
PDF: 7 pages
Proc. SPIE 7038, Optical Trapping and Optical Micromanipulation V, 70381X (29 August 2008); doi: 10.1117/12.793428
Show Author Affiliations
E. Schonbrun, Harvard Univ. (United States)
K. B. Crozier, Harvard Univ. (United States)

Published in SPIE Proceedings Vol. 7038:
Optical Trapping and Optical Micromanipulation V
Kishan Dholakia; Gabriel C. Spalding, Editor(s)

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