Optical trapping near a colloidal cluster formed by a weakly focused laser beam

Abstract

We report on the results of our studies on the stable trapping of colloidal particles by a cluster of microspheres formed using a weakly focused trapping laser beam. Since the observed trapping action was believed to arise due to interference of the coherently scattered optical fields from this multiparticle cluster, experiments were carried out on a one-dimensional chain of polystyrene microspheres, which is simpler to model. A chain of three microspheres, which was generated using an elliptical trap beam, was observed to trap a microsphere at a distance of about ~3 μm on its symmetry axis. This is in reasonable agreement with the trapping sites predicted based on the calculated intensity pattern of the coherently scattered optical fields from this multiparticle cluster.