Soliton interactions and transformations in colloidal media

We study nonlinear light propagation in colloidal suspensions of spherical dielectric nanoparticles. We analyze the existence and properties of one-dimensional self-trapped beams (spatial optical solitons) in such media and demonstrate the existence of a bistability regime. The solitons corresponding to the two bistable branches have very different properties, and they can be easily distinguished by the measurement of the soliton width. We find that both types of solitons can form spontaneously through spatial modulational instability of continuous wave beams, but the solitons corresponding to the upper branch are more robust. This is also confirmed by the study of soliton collisions, where we describe a number of possible scenarios, including soliton amalgamation, destruction, reflection, deflection, and switching to another branch. We also find that the interaction of two mutually coherent solitons corresponding to different branches is phase independent and always repulsive. We provide a simple physical explanation of this phenomenon.