Guiding lasers to where they need to go is a key part of the optical system, and now DESY engineers have developed a way to bend the laser beam without touching anything. An invisible grating made of air using acoustic principles can deflect light.


Artist’s impression of an air grating that bends laser beams/United Nations Decade of Education for Sustainable Development (DESY) Science Communication Laboratory

In optical systems, laser light is typically redirected through lenses and mirrors, but in high-energy situations, such as lasers used in materials processing, particle accelerators, or fusion energy research, these fragile parts may need to be replaced frequently.

Christoph Heyl, the lead researcher on the new project, said: "In this power range, the material properties of mirrors, lenses and prisms greatly limit their use. In practical applications, these optical elements can be easily damaged by powerful laser beams. In addition, the quality of the laser beam can also be affected. In contrast, we have successfully deflected the laser beam without contact, thus ensuring the quality of the laser beam."

The DESY team's alternative is to use acoustic principles to sculpt the air. Sound waves are essentially just changes in air pressure, so turning up the volume loud enough can create sound waves powerful enough to levitate objects, or in this case, manipulate light itself.

The researchers used a pair of ultrasonic speakers facing each other to create pockets of denser or lower density air, creating a striped grating pattern. When an infrared laser beam passes through this grating, the light deflection efficiency exceeds 50%. The team says even greater efficiencies could be achieved with further work.

These tests involve quite powerful equipment - the lasers have a power of up to 20 gigawatts, and the speakers need to reach a volume of 140 decibels, which is the volume of a jet engine a few meters away. But thankfully, since it is ultrasound, it cannot be detected by the human ear.

The team says this technique could serve as a fast switch for lasers, and future work could try forming shapes other than gratings, including lenses and waveguides. Also, they don't need to be limited to ordinary air. "

"First, we tried our technology with regular air," Haier said. "Next, we will also use other gases to take advantage of other wavelengths, other optical properties and geometries."

The research was published in the journal Nature Photonics.