Feedback-enhanced optical trapping force using a semiconductor laser

Abstract

We report a technique for enhanced trapping ofa microsphere using a low-power semiconductor laser. A gain in gradient trapping force is achieved by recycling the transmitted light through the sample back to the focal area consequently increasing the E-field necessary to trap the particle as well intensifying the laser power due to the presence of an external cavity (optical feedback). A semiconductor laser diode using an output power ~10 mW provides enough power to trap 3 and 5 μm sized polystyrene beads. The trappingforce increased by ~32% corresponding to an increase in optical power due to optical feedback.