Random Light-Absorbing Lasers


Teresa Feng, Staff Writer

   On March 4, 2019, the Vienna University of Technology announced it had developed a method in which a laser can absorb light, and then dissipate the energy. Through a technique called random scattering, Professor Stefan Rotter and his team have reversed the idea of a laser, with a device that absorbs light instead of emitting it. With the help of the University of Nice and many computer simulations, Rotter has built a prototype of the ‘random anti-laser’. This discovery provides more possibilities in other scientific fields, such as medicine and technology.  

   Light waves scattered randomly in all directions are everywhere. For example, the signal of a mobile phone is reflected many times before reaching the phone. In Science and Technology Research News, Rotter states, “This multiple scattering is made practical use of in so-called random lasers.”  In the anti-laser, the waves that are dispersed and absorbed must have the right color and space between them. Then, the energy is dissipated, similar to a video of a laser played in reverse. A laser produces a specific wave based on its random inner structure, so the absorbed waves must also be a particular color. The absorber does not have to be exceptionally strong, because due to random scattering, one wave splits into many partial waves. These separated waves then overlap and interfere with each other in a way that does not allow any to escape, leaving them successfully trapped and absorbed.

   Rotter and his team built a prototype of an anti-laser with several methods in mind. Anti-lasers are currently restricted to one dimensional structures. According to Science Daily, the scientists decided, “Our approach is much more general: we were able to show that even arbitrarily complicated structures in two or three dimensions can perfectly absorb a suitably tailored wave. In this way, this novel concept can also be used for a much wider range of applications.” By bringing out the versatility of the concept, this new idea stands out from other similar devices. The team used Teflon cylinders and placed them randomly so the waves would reflect off them like they would in the real world. They broadcasted signals through the newly created environment, and found that 99.8% was absorbed by an antennae with a waveguide placed on it. Researchers see this as a promising step towards an anti-laser that can be used in daily life. Many aspects of the anti-laser still have to be carefully calibrated, such as the absorption strength of the antennae and signal frequency.

   Rotter predicts reversing the concept of the laser can be used in areas of science and engineering related to wave phenomena. Science Alert reports Rotter saying, “‘Also in medicine, we often deal with the task of delivering wave energy to a very specific point – such as shock waves shattering a kidney stone.’” In phones, the anti-laser could adjust the signal exactly, so it is completely absorbed into the antennae. Rotter´s team wants to be able to use the anti-laser for a variety of uses, which would benefit various fields and the people involved.