Interferometric optical tweezers

We report the first experimental demonstration of an optical trap that uses interference fringes for the trapping and micro-manipulation of microscopic objects. The fringes can be generated either by two-beam interference or by projecting a reduced image of a Ronchi ruling on the sample plane. Polystyrene beads of a few microns in diameter can be trapped and held in a bright region of a set of interference fringes and subsequently moved to a designated position by sweeping the fringes across the field of view. The potential advantages of extending this technique to the trapping of rod-shaped samples and for independent micro-manipulation of two or more particles are discussed.