Position clamping in a holographic counterpropagating optical trap

Bowman, R., Jesacher, A., Thalhammer, G., Gibson, G. , Ritsch-Marte, M. and Padgett, M. (2011) Position clamping in a holographic counterpropagating optical trap. Optics Express, 19(10), pp. 9908-9914. (doi: 10.1364/OE.19.009908)

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Optical traps consisting of two counterpropagating, divergent beams of light allow relatively high forces to be exerted along the optical axis by turning off one beam, however the axial stiffness of the trap is generally low due to the lower numerical apertures typically used. Using a high speed spatial light modulator and CMOS camera, we demonstrate 3D servocontrol of a trapped particle, increasing the stiffness from 0.004 to 1.5μNm<sup>−1</sup>. This is achieved in the “macro-tweezers” geometry [Thalhammer, J. Opt. 13, 044024 (2011); Pitzek, Opt. Express 17, 19414 (2009)], which has a much larger field of view and working distance than single-beam tweezers due to its lower numerical aperture requirements. Using a 10×, 0.2NA objective, active feedback produces a trap with similar effective stiffness to a conventional single-beam gradient trap, of order 1μNm<sup>−1</sup> in 3D. Our control loop has a round-trip latency of 10ms, leading to a resonance at 20Hz. This is sufficient bandwidth to reduce the position fluctuations of a 10μm bead due to Brownian motion by two orders of magnitude. This approach can be trivially extended to multiple particles, and we show three simultaneously position-clamped beads.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Gibson, Dr Graham and Padgett, Professor Miles and Bowman, Mr Richard
Authors: Bowman, R., Jesacher, A., Thalhammer, G., Gibson, G., Ritsch-Marte, M., and Padgett, M.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Optics Express
Publisher:Optical Society of America
ISSN (Online):1094-4087
Published Online:05 May 2011
Copyright Holders:Copyright © 2011 Optical Society of America
First Published:First published in Optics Express 19(10):9908-9914
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
566181Optical Tweezers at Long Range and High Pressure (Creativity @ Home)Miles PadgettEngineering & Physical Sciences Research Council (EPSRC)EP/I034726/1Physics and Astronomy