Real-time interactive optical micromanipulation of a mixture of high- and low-index particles

We demonstrate real-time interactive optical micromanipulation of a colloidal mixture consisting of particles with both lower (n(L) < n(0)) and higher (n(H) > n(0)) refractive indices than that of the suspending medium (n(0)). Spherical high- and low-index particles are trapped in the transverse plane by an array of confining optical potentials created by trapping beams with top-hat and annular cross-sectional intensity profiles, respectively. The applied method offers extensive reconfigurability in the spatial distribution and individual geometry of the optical traps. We experimentally demonstrate this unique feature by simultaneously trapping and independently manipulating various sizes of spherical soda lime micro shells (n(L) approximate to 1.2) and polystyrene micro-beads (n(H) = 1.57) suspended in water (n(0) = 1.33). (C) 2004 Optical Society of America.