Scanning mirror on a vibrating membrane for dynamic optical trapping
We report a simple technique for the dynamic optical trapping of colloidal particles. The main feature of this technique is an addition of a scanning mirror on a vibrating membrane in the optical train of a typical optical tweezers setup. When the membrane is vibrated using sound input from a normal speaker, the laser beam that is reflected off the mirror traces out a wide variety of laser patterns of Lissajous figures depending on the input sound frequency and amplitude. The resultant pattern is subsequently focused down by a laser tweezers setup onto an aqueous suspension of monodispersed polystyrene microspheres. As a result, a wide variety of planar assemblies of the colloidal microspheres corresponding to the laser patterns are organized. In addition to the optical trapping force, the scanning laser also exerts a driving force on the microspheres. Optically assisted assemblies of microspheres can hence be manipulated to translate along the laser scanning pattern. In an elliptically patterned optical trap, repetitive scanning of the focused laser beam over an assembly of optically trapped microspheres drives the microspheres into rotation.
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