On- and off-axis binding and induced circulation in counter-propagating beam traps

Optically bound arrays of microparticles in counter-propagating laser traps are typically constrained to the beam axis. Here we discuss the mechanisms underlying the formation of these chains, and report on binding where the particles are displaced from the beam axis. We also describe circulatory motion of the bound arrays around the beam axis. We show both experimental results and a Mie scattering simulation, and discuss the physical basis for the effects.