Size selective trapping with optical ”cogwheel” tweezers

Author(s): Alexander Jesacher, Severin Fürhapter, Stefan Bernet, and Monika Ritsch-Marte


“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.”

Link to Publications Page

Publication: Optics Express
Issue/Year: Optics Express, Vol. 12, Issue 17, pp. 4129-4135, 2004
DOI: 10.1364/OPEX.12.004129