Acousto optic modulation of gigawatt level laser pulses in the ambient air of Nature Photonics

An interdisciplinary research group, including the German synchrotron radiation accelerator DESY and the Helmholtz Institute in Jena, Germany, reported that invisible gratings made of air not only are not damaged by lasers, but also maintain the original quality of the beam. The relevant research has been published in Nature Photonics under the title of "Acousto opt modulation of gigawatt scale laser pulses in ambient air".

From gravitational wave astronomy, quantum metrology, ultrafast science, to semiconductor manufacturing, controlling the intensity, shape, direction, and phase of coherent light is crucial in many fields. However, modern photonics may involve parameter regions where wavelength or high optical power limits control due to absorption, light induced damage, or optical nonlinearity in solid media. Here, researchers suggest using high-strength ultrasound customized gaseous media to avoid these limitations.

Source: DESY Science Communication Laboratory
Researchers demonstrated the implementation of this method by effectively deflecting ultrashort laser pulses in ambient air using ultrasound without the need for transmitting solid media. At a peak optical power of 20 GW, the deflection efficiency of the researchers exceeded 50% while maintaining excellent beam quality, exceeding the limit of previous solid-state based acoustooptic modulation by about three orders of magnitude. The researchers' methods are not limited to laser pulse deflection; The gas-phase photon scheme controlled by sound waves may be used to implement new optical components such as lenses or waveguides, which can effectively resist damage and operate in new spectral regions.

Schematic diagram of angle deflection of ultrasonic assisted laser beam in air.

This innovative technology utilizes sound waves to modulate the air in the area where the laser beam passes through. Researchers have generated an invisible grating using acoustic density waves.

With the help of special speakers, researchers have formed areas of high and low density in the air, forming stripe gratings. Due to the difference in air density, the light in the Earth's atmosphere bends, so this density pattern acts as a grating, changing the direction of the laser beam.

The relationship between experimental setup and deflection efficiency with sound power and time.

In the first laboratory test, the efficiency of reorienting strong infrared laser pulses in this way was 50%. According to the numerical model, higher efficiency should be achieved in the future.

The research team believes that this technology has great potential in the field of high-performance optics. In the experiment, researchers used infrared laser pulses with a peak power of 20 gigawatts, which is equivalent to the power of approximately 2 billion LED bulbs. This type of laser with even higher power levels can be used for material processing, nuclear fusion research, or the latest particle accelerators.

AO diffraction of ultra short laser pulses at high peak power.
Scientists emphasize that the principle of acoustic control of lasers in gases is not limited to the generation of optical gratings. It is likely to be applied to other optical components such as lenses and waveguides.

The technology of directly deflecting light in ambient air has been confirmed, opening up promising applications, especially as a fast switch for high-power lasers. Modern optics is almost entirely based on the interaction between light and solid matter. The researchers' methods have opened up a new research direction.

Related paper links:
Yannick Schrödel et al, Acousto-optic modulation of gigawatt-scale laser pulses in ambient air, Nature Photonics (2023). DOI: 10.1038/s41566-023-01304-y
https://phys.org/news/2023-10-air-deflect-lasers.html

Source: Yangtze River Delta Laser Alliance