Using the geometry of the laser, researchers at the University of Witwatersrand's laser for the first time implemented a method of changing the orbital angular momentum of a laser beam.
"Nature Photonics" NaturePhotonics magazine published research on this new type of laser, discovered by researchers in South Africa and Italy, that produces a "warped" laser beam as its output. Laser output and a new type of laser laser beam formed by the superposition, known as the vector vortex beam. For the first time, the geometric phase in lasers is exploited, opening the way for new lasers in applications such as optical communications, laser processing, biomedicine and the like.
The idea was envisioned by Professor Forde Forbes of WITS and led the entire collaborative research, with all the key experiments being conducted by the Council of Scientific and Industrial Research (CSIR ) By Dr. Darryl Netto.
Team members, Professor Steve Roue, Dr. Angela Dudley, and Dr. Igor Litte make a significant contribution to this endeavor. Without this idea, custom geometry phase optics would not be possible to experiment with and was proposed by a research team at the University of Naples, Italy, including Professor Lorenzo Marucci and Professor Bruno Picchilo .
"We are all familiar with the angular momentum of everyday life: Rotating Earth carries spin angular momentum, Orbital Angular Momentum (OAM) around the Earth. Light can also carry angular momentum: through its polarization (spin) and through The mode and phase of the orbital angular momentum, "Forbes said.
It has been decades since the laser controlled the spin to produce light, but the orbital angular momentum produced in the laser was not that simple. The light-loaded orbit angular momentum is created by twisting the phase of the light into a spiral that forms a spiral.
Since the closer to the center of the beam, the warping of the modes gets tighter until the light disappears, and such beams are often referred to as annular beams or vortex beams. The problem is that usually the laser does not tell if the light is rotating clockwise or the light is rotating counterclockwise, so the laser is just a combination that is done in an uncontrolled manner.
In addition, the beam produced by a single laser in combination with the spin and orbital components is a mixture of two momentums, which was previously unverified.
"Our novelty is the realization that by drawing the orbital angular momentum using custom geometry-phase polarization optics, the laser can tell the difference between clockwise and counter-clockwise light," Forbes said.
Control is achieved by simply rotating a single optical element in the laser without any other adjustments required. Such beams have been used for optical communications, optical particle capture and metering, and can now be created on demand by a single laser.
The geometric phase of light is a very abstract concept, first appearing in quantum theory, but researchers here have used it to create a particular type of distorted light. Custom light, called the q-plate, adjusts the orbital angular momentum deflection according to the polarization torsion characteristics, from one map to another.
For example, if the clockwise polarized light passes through the optical fiber without twisting it, the output is polarized light in the counterclockwise direction and the phase is twisted clockwise. The output is also controllable by applying these elements to the laser and the polarization twist (rotation) controlling the direction of twist of the orbital angular momentum. "We like to call this a helical laser, because the beam's polarization and orbital angular momentum work in the generation of light and rotate or twist in a complicated way," Forbes said.
Importantly, the same laser can produce any combination of these orbital angular momentum beams and various polarized beams. The team also found that the light output was generated by an arbitrary vector vortex beam called the higher order Poincaré sphere beam.
For example, with the exception of the special case of an orbital angular momentum beam, the same laser produces both radial and angularly polarized light, with the polarization (electric field direction) varying spatially. For example, radial polarized light always points away from the center of the circle, which is very useful when cutting metals.
This type of beam is often referred to as a "vector" beam because polarization changes across the beam. When the polarization mode remains constant throughout the beam, it is called a "scalar" beam. In the paper, researchers have shown that both of these beams can be created by the same laser.
"It has to be understood that vector eddy-current laser beams have proven to be very useful in the machining of metals and other materials, for example in the automotive industry, but until now we can not produce all of these beams in the same laser, Du says the ongoing experiment is also part of his own Ph.D. research and is also the lead author of the paper.
The concept of laser is likely to attract interest from academia and industry. Vector and scalar vortex beams with higher orders of Poincaré sphere have many applications, such as microscope imaging, laser processing, and can be used for free space and fiber optic communications. Often it is up to you to decide which kind of light beam you want most and then to design a laser. Now it becomes possible to meet the needs of different laser beams with a single laser.