Light has been "tied in knots" by physicists working at the universities of Bristol, Glasgow and Southampton.
The light was controlled using holograms specially designed with "knot theory" - a branch of abstract mathematics inspired by twists in shoelaces and rope.
The breakthrough paves the way for a new level of precision in laser technology, with applications ranging from traffic speed guns to height measurement.
Dr Mark Dennis from the University of Bristol said: "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'.
"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."
The team were able to create knots in optical vortices, using the sophisticated holograms to direct the flow of light, said Dr Dennis, lead author on the paper published in Nature Physics.
This research demonstrates a physical application for a branch of mathematics previously considered completely abstract.
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."
Dr Dennis added: "The study of knotted vortices was initiated by Lord Kelvin back in 1867 in his quest for an explanation of atoms. This work opens a new chapter in that history."