Laser deflected using air alone

An interdisciplinary research team has unveiled a groundbreaking method in the journal Nature Photonics: they’ve found a way to deflect laser beams using nothing but air. This revolutionary technique creates an invisible grating composed solely of air, which not only remains impervious to laser damage but also maintains the beam’s original quality. The researchers have even filed a patent application for their innovative method.

This novel approach harnesses the power of sound waves to modulate the air in the laser beam’s path. Yannick Schrödel, a Ph.D. student at DESY and Helmholtz Institute Jena and the first author of the study, explains, “We’ve created an optical grating using acoustic density waves.”

To achieve this, the research team employs specialized loudspeakers to shape a pattern of alternating dense and less dense areas in the air, forming a striped grating. Much like how variations in air density bend light in Earth’s atmosphere, this density pattern acts as an optical grating, altering the laser beam’s trajectory.

Schrödel points out, “Deflecting light through a diffraction grating allows for significantly more precise control of the laser light compared to natural atmospheric deflection.” The properties of this optical grating are influenced by the frequency and intensity, essentially the volume, of the sound waves.

In initial laboratory tests, the researchers achieved a 50 percent efficiency in redirecting a powerful infrared laser pulse using this method. Numerical models suggest that even higher efficiencies can be achieved in the future.

In this animation, a laser light beam passes between a loudspeaker-reflector array that creates a grating of air. The laser beam interacts with this grating and is deflected without contact. Credit: Science Communication Lab for DESY

In their initial test, the scientists had to crank up their specialized loudspeakers to the max. “We’re talking about sound levels reaching approximately 140 decibels, akin to a jet engine roaring just a few meters away,” elaborates Christoph Heyl, the lead researcher from DESY and the Helmholtz Institute Jena. “Luckily, we’re working in the ultrasound range, which our ears can’t detect.”

The research team envisions tremendous potential for this technique in high-performance optics. In their experiments, they utilized an infrared laser pulse boasting a peak power of 20 gigawatts, equivalent to the output of roughly two billion LED bulbs. Such high-power lasers are utilized in various applications, from material processing to fusion research and cutting-edge particle accelerators.

Heyl clarifies, “In this power range, conventional optical components like mirrors, lenses, and prisms face significant limitations and are susceptible to damage from intense laser beams. Moreover, the laser beam’s quality deteriorates. In contrast, we’ve achieved laser beam deflection while preserving its quality without any physical contact.”

The concept of using acoustics to control laser light in gases extends beyond generating optical gratings, the scientists emphasize. It likely holds promise for other optical elements such as lenses and waveguides.

“We’ve contemplated this method for quite some time and initially thought that achieving such extreme sound levels would be technically unattainable,” Heyl reveals. “However, we persisted and ultimately found a solution with the assistance of researchers from the Technical University of Darmstadt and the company Inoson. Initially, we experimented with regular air. Next, we plan to explore other gases to access different wavelengths and optical properties.”

The ability to deflect light directly into the surrounding air, as already demonstrated, presents exciting applications, particularly as a rapid switch for high-power lasers. Heyl adds, “The potential of controlling light without physical contact and expanding it to other applications is currently beyond imagination. Modern optics primarily relies on interactions with solid matter, but our approach charts an entirely new course.”

Source: Deutsches Elektronen-Synchrotron

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