Today’s Tech Photo: Twisted laser beams

A research team from South Africa and Italy has demonstrated a new kind of laser that can produce beams “with a twist” as its output. The outputs and superpositions of the new type of laser form a set of beams, called vector vortex beams.

The discovery opens the door to new kinds of lasers for optical communication, laser machining and medicine applications.

This is an artist's impression of spiral light created at source. (Image Credit: Marko Mandusic)
This is an artist’s impression of spiral light created at source. (Image Credit: Marko Mandusic)

While producing light with a controlled spin in a laser is not a novel concept, producing orbital angular momentum (OAM) beams inside a laser is not an easy task. Light carrying OAM is created by twisting the phase of light into a helical shape, forming a spiral. The twisting of the pattern gets tighter and tighter as you move towards the center of the beam, the light disappears. These beams are often called doughnut beams or vortex beams. The problem is that usually lasers cannot tell the difference between light that is twisted clockwise and light that is twisted counter-clockwise, so the laser gives a combination of both in an uncontrolled manner. In addition, combining spin and orbital components to produce general beams from a single laser that are mixtures of the two momenta, has not been demonstrated before.

“Our novelty was to realize that by using custom-geometric phase optics to map polarization to OAM, the laser could be designed to tell the difference between the clockwise and anticlockwise light,” said Andrew Forbes of the University of the Witwatersrand (Wits), who also led the collaboration. The control is achieved by simply rotating a single optical element inside the laser, without any need for realignment. Such beams have been used in optical communication, optical trapping of microparticles and metrology – and now a single laser can create them on demand.

According to the researchers, the new laser concept will probably be of interest to both the academic and industrial communities. Vector and scalar vortex beams that exist on the higher-order Poincaré sphere have many applications, such as microscopy, imaging, laser machining, and communication in free space and in fibers. Typically,  you have to decide beforehand which beam is the most desirable and then design a laser for it, but now it is possible to have such beams available on demand from a single laser.


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