Dynamics of mixed refractive index particles in complex fields

We consider a system of colloidal particles, with two or more different refractive indices, which stick together to form mixed clusters. The behaviour of such clusters in optical traps will vary depending on the numbers of particles involved and the distribution of their refractive indices. Our own recent studies of heterodimers of such beads suggest there is a rich vein of novel behaviour to explore, including unusual dynamics and optical binding [O'Donnell et al. Proc. SPIE 12436, 124360J (2023)]. In the present computational study we will explore the dynamics of mixed refractive index clusters in different types of optical trap, as a function of number and composition of beads as well as their arrangement. In particular, we will highlighting the difference between symmetrical and asymmetrical arrangements of beads in conventional Gaussian beams as well as in OAM beams. The optics model used is based on the discrete dipole approximation and includes low Reynolds number hydrodynamics with bead separations maintained using SHAKE-HI constraints. Further studies will investigate optical binding between arrays of such clusters in different types of structured fields.