  We study the effects of the optical binding force on wavelength sized
colloidal particles free to move in a counter-propagating beam. This work is
motivated by the concept of using optical binding to direct the assembly of
large numbers of colloidal particles; previous work has used small numbers of
particles and/or 1D or 2D restricted geometries. Utilizing a novel experimental
scheme, we describe the general static and dynamic self-organization behaviors
for 20--100 particles free to move in 3-dimensional space. We observe the
self-organization of the colloids into large optically bound structures along
with the formation of driven particle clusters. Furthermore we show that the
structure and behavior of these optically bound systems can be tuned using the
refractive index of the particles and properties of the binding light. In
particular, we show that the driven behavior originates from $N$-body
interactions, which has significant implications for future work on optically
bound clusters of more than 2 particles.
