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Opt Express. 2004 Aug 23;12(17):4129-35.

Size selective trapping with optical "cogwheel" tweezers.

Abstract

We experimentally investigate the size-selective trapping behavior of Laguerre-Gaussian beams ("doughnut-beams") and "cogwheel"-shaped beams which are collinear superpositions of two doughnut beams of equal opposite helical index. Experimentally they are created by diffraction of a Gaussian laser beam at a high resolution refractive spatial light modulator (SLM). In the focus of an optical microscope such a beam looks similar to a "cogwheel", i.e. the light intensity is periodically modulated around the circumference of a sphere with a precisely adjustable diameter. In an optical tweezers setup these modes can be used to trap particles or cells, provided their sizes exceed the ring diameter by a fixed amount. This promises a convenient method of constructing an optical tweezers system in microscopy which acts as a passive sorter for particles of differing sizes.

PMID:
19483955
DOI:
10.1364/opex.12.004129

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