Abstract

It was recently demonstrated that low-index spherical dielectric particles could be stably trapped by use of a strongly focused stationary laser beam containing an optical vortex.¹ Optical vortices have also been shown to improve the efficiency of gradient force traps, thus reducing damage to biological systems.² Further, vortex beams are capable of transferring angular momentum to slightly absorbing trapped particles.³ In this paper we report the first observation, to our knowledge, of simultaneous trapping of both a low-index and high-index particle in a single beam. The offset between stable trapping positions for these two types of particles makes such a configuration possible for certain sized particles. We also report experimental measurements of the point of stable equilibrium for a low-index particle in an optical vortex trap.

© 1997 Optical Society of America