Light beams tied in knots

Researchers from the British universities of Southampton and Glasgow have succeeded in tying knots in light beams.

Using a computer-designed hologram, they created threads of darkness embedded in a laser beam.

The hologram bends the direction of optical energy flow, so these dark threads form loops. The loops can then be linked together, or 'tied into knots'.

Dr Mark Dennis, a Southampton University mathematician, worked in collaboration with Prof Miles Padgett, Dr Johannes Courtial and Jonathan Leach in the optics group in Glasgow University's Department of Physics & Astronomy.

Dr Dennis made the detailed calculations required to find the ideal mathematical form for the knotted laser beams.

The role of the Glasgow group was in designing the hologram that produced the exact combination of beams required to form the loops and knots. A laser was used to illuminate the hologram and the detailed structures recorded by a sensitive camera.

This work is experimental confirmation of earlier theoretical predictions made by Dr Dennis, with Prof Sir Michael Berry at the University of Bristol.

Scientifically the work dates from Lord Kelvin who tried to formulate a theory for atoms made of loops and knots, embedded not within light, but in the fictitious ether.