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Laser Trapping: Experimenting with Dielectric Particles

Sven Woldberg

Centre for Micro-Photonics, Swinburne University of Technology

3.30pm, Thursday 14 June 2001, Seminar Room (AR103), Graduate Research School

The study of single biological molecules, like enzymes and DNA, has been growing rapidly in the recent years. This is because single (bio) molecule studies reveal new levels of information. Traditional biochemical techniques allow experiments on large numbers of molecules all at the same time. This results in the detection of averaged behaviour and slow dynamics. However, for biological molecules it is the three dimensional structure, which is very important. It dictates for a large part the biological function of the macromolecule.

The rise of powerful new techniques, like atomic force microscopy (AFM), laser traps, fluorescence resonance energy transfer, etc, made it possible to look at, manipulate and study single bio-molecules. One of the major tools of single molecule experiments has been laser trapping. Laser traps (or optical tweezers) rely on radiation pressure. Radiation pressure generally refers to forces imparted to matter by absorption, scattering, emission, or re-radiation of light. The radiation pressure allows objects to be held stably in a focussed laser beam. These optical forces arise from a change in momentum of the laser light.

The dependence of the trapping efficiency for a uniform laser beam on 2-micron polystyrene beads has been experimentally determined for different sizes of annular obstructions. A distinction has been made between s- and p-polarised laser light. The results of a transverse trapping efficiency on dielectric beads versus annular size have to date never been published. An insight in laser trapping and its applications as well as the results obtained at the Centre for Micro-Photonics are given in this talk.

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