Knit one, purl one: physicists tie light in knots

It all sounds a bit Harry Potter, but a team of British scientists has managed to tie light in knots, an achievement that could have important implications for laser technology.

“In a light beam, the flow of light through space is similar to water flowing in a river. Although it often flows in a straight line – out of a torch, laser pointer, etc – light can also flow in whirls and eddies, forming lines in space called ‘optical vortices'”, Dr Mark Dennis from the University of Bristol and lead author on the paper, explains.

“Along these lines, or optical vortices, the intensity of the light is zero (black). The light all around us is filled with these dark lines, even though we can’t see them.”

To create optical vortices, the team used holograms to direct the flow of light. They designed the holograms using knot theory – a branch of abstract mathematics previously considered completely abstract. Using these specially designed holograms they were able to create knots in optical vortices.

Professor Miles Padgett from Glasgow University, who led the experiments, said: “The sophisticated hologram design required for the experimental demonstration of the knotted light shows advanced optical control, which undoubtedly can be used in future laser devices.”

“The study of knotted vortices was initiated by Lord Kelvin back in 1867 in his quest for an explanation of atoms,” added Dennis. “This work opens a new chapter in that history.”

Details appear in Nature Physics.