Laser Beams Tied in Knots

Scientists at the University of Glasgow and the University of Southampton, both in the UK, reported in the Nov. 11 issue of Nature the formation of link and knot structures from dark lines embedded within Laguerre-Gaussian laser beams. The experiment confirms theoretical predictions regarding the creation of phase singularities, and the work may find application in the confinement of ultracold atoms and Bose-Einstein condensates.

The structures are defined by the coaxial superposition of four HeNe laser beams that pass through a programmable spatial light modulator. Three of the beams have vortices along the beam axis of the same strength but with different numbers of nodal rings around the axis and with different continuous waist widths. The fourth beam is a simple Gaussian beam. Depending on the strength of the vortices, the beams form linked loops or a trefoil knot.