Phase Contrast Produces Dynamic, Multiple-Beam Optical Tweezers

Using generalized, phase-contrast-based encoding onto a spatial light modulator, researchers at the Risø National Laboratory in Roskilde, Denmark, have demonstrated a nonmechanical method to produce an array of optical trapping beams whose position, size, shape and intensity can be individually manipulated. They created the trapping patterns on the parallel-aligned, liquid-crystal-type light modulator from Hamamatsu Photonics with a Sony VGA-resolution liquid crystal projector element controlled by a PC. The modulator divided the beam from a 200-mW, 830-nm SDL diode laser into multiple optical trapping beams with approximately 1.3 mW of power. As described in the July 15 issue of Optics Express, the researchers used the system to "mouse control" as many as 16 2-µm polystyrene beads simultaneously.