Photons usually go straight, but their magnification power increases if they whirl
An international team of researchers from the Instituto Superior Técnico (IST) in Portugal, the Rutherford Appleton Laboratory (UK), Strathclyde University (UK) and Oxford University (UK) has developed a concept to generate photons that whirl at high speed.
The team found a new way to control the whirling motion of photons. This work may influence the development of new generations of super-resolution microscopes for imaging in medicine and science. The discovery has been published in the December 23rd issue of Physical Review Letters (DOI: 10.1103/PhysRevLett.117.265001).
An optical vortex is an unusual light form, where the photon beam rotates, forming an electromagnetic field structure that resembles a tornado. Far from a mere scientific curiosity, optical vortices have an outstanding potential to revolutionise key technologies of modern society. One of the most promising areas is the potential to develop optical microscopes with magnification powers that greatly exceed classical limits.
Scientists have found that the faster the photons whirl, the greater their potential for magnification. One of the challenges for the development of advanced microscopy techniques based on optical vortices resides in the difficulty of increasing their rotation speed independently of any other property. Showing that this can be achieved is an outstanding technological and scientific challenge.
The research team has now obtained a solution to this problem. This solution makes use of the unusual optical properties of ionised gas, or plasma. Independent laser beams interact with each other when they meet in plasma, producing light vortices that spin much faster than previously thought possible.
The team of physicists have developed analytical solutions showing this behaviour, and confirmed their predictions with the aid of advanced computer simulations. The numerical simulations were carried out using the Fermi petaflop supercomputer in Bologna, Italy.
According to Bob Bingham, a Professor of physics at the University of Strathclyde and the STFC Rutherford Appleton Laboratory in the UK: “This work allows one to take full advantage of optical vortices for a number of applications including coding in optical communications.” The conclusions of this work may also easily be transported to other disciplines such as super resolution microscopy, leading to very powerful optical microscopes.
Image of an optical vortex. The helical structures in blue are the typical signatures of an optical vortex.
Image of a laser containing photons with very high spinning velocities.