Colloidal holography and crystal dislocations

The analogous nature of dislocations in crystals and light leads to some interesting links between the properties of optical and crystal dislocations. A dislocation in a crystal can be described by a Burgers vector b, whilst a dislocation in a laser mode such as the vortex in a Laguerre Gaussian beam, can be described by a topological charge l2. By illuminating both optically trapped and self-assembled two-dimensional colloidal crystals with a Gaussian laser beam, we show a direct link between crystal and light dislocations, where the first order diffraction pattern from a crystal with Burgers' vector b = na contains vortex laser modes of topological charge l=±mn, (where n is an integer, a is the lattice constant of the crystal and m is an integer corresponding to the diffraction order).