Theory and simulation of the bistable behaviour of optically bound particles in the Mie size regime

Optical binding refers to the light-induced organization and ordering of microparticles. In this paper, we present a theoretical treatment of optical binding in the Mie size regime using the paraxial approximation for field propagation combined with the Lorentz force law. Experimental studies of the separation between two dielectric spheres in a counter-propagating (CP) geometry are compared to numerical predictions. We explore the bistable nature of the bound sphere separation and its dependency on the refractive index mismatch between the spheres and the host medium, with an emphasis on the fibre separation and adiabaticity of the system.