Vortex knots in light

Optical vortices generically arise when optical beams are combined. Recently, we reported how several laser beams containing optical vortices could be combined to form optical vortex loops, links and knots embedded in a light beam (Leach et al 2004). Here, we describe in detail the experiments in which vortex loops form these structures. The experimental construction follows a theoretical model originally proposed by Berry and Dennis, and the beams are synthesised using a programmable spatial light modulator and imaged using a CCD camera. PACS numbers: 03.65.Vf, 02.10.Kn, 42.25.Hz, 42.40.Jv Optical vortices (phase singularities, wave dislocations) are ubiquitous in nature, occurring whenever three or more light waves interfere. They are places in the interference field where the intensity is zero, and the phase is undefined, and usually occur at points in 2-dimensional fields, and along lines in 3 dimensions (see, for example, 1, 2, 3). Within the laboratory, vortices are commonly produced using computer generated holograms or diffractive optics. Holograms of the design originally demonstrated by 4, 5 are now widely used to create light beams with vortices embedded,