Boundary effects on the dynamics of higher-order optical spatial solitons in nonlocal thermal media

We study theoretically the propagation of higher-order two-dimensional spatial solitons in optical media with nonlocal thermal nonlinear response. We show that these localized states experience complex dynamics including transformations between solitons of different symmetries which depend strongly on the geometry of a nonlinear sample. Boundaries exert repulsive forces on a soliton and, depending on its initial position relative to the boundaries, we observe transverse motion of a beam as a whole across the sample, effectively facilitating transformations.