Optical trapping and binding of mixed refractive index particles

In this computational study we examine the behaviour of mixed-refractive index colloidal clusters. The clusters consist of bonded collections of spherical nanospheres with different refractive indices. The behaviour of these clusters in optical traps varies depending on the numbers of particles involved and the overall symmetry of the cluster. The symmetry can be varied by changing the refractive indices. It has been shown that breaking the symmetry of a cluster by, for example, introducing a single high refractive index impurity can produce a pronounced impact on the dynamics of the cluster in an optical trap [Davie et al. Proc. SPIE 12649, 126490E (2023)]. In the present study we will explore the dynamics of mixed refractive index clusters counter propagating plane waves and in different types of optical trap. Optical forces are calculated using the discrete dipole approximation; dynamics are computed using Brownian dynamics, with hydrodynamic interactions in the low Reynolds number regime and particle separations are constrained using the SHAKE-HI algorithm.