Lasers & Sources

Diamond Raman laser could have higher power and efficiency for telescope adaptive optics

April 3, 2020

Emitting at the yellow sodium line, a diamond Raman laser could also enable more point-like guide stars to be generated through AO systems.

John Wallace

This diamond Raman laser produced by researchers at Macquarie University is pumped with light at 1018 nm to produce a 1178 nm output, which is then frequency-doubled to the 589 nm yellow sodium line. Used to produce guide stars in the upper atmosphere for adaptive optical systems in large ground-based telescopes, such a laser can do so at higher efficiency than existing lasers.

Lasers that emit light at the sodium line (actually a doublet) at a wavelength of about 589 nm are used to produce artificial "guide stars" in the mesosphere at an altitude of around 90 km for use with adaptive optical (AO) systems integrated with large ground-based astronomical telescopes. These artificial stars allow astronomers to use AO to correct atmospheric aberrations of light passing to and from space. An additional use for this technology is earth-to-space communications.

Now, researchers at Macquarie University (Sydney, Australia) have developed what they say is an improved laser system for these purposes: a continuous-wave diamond Raman laser emitting at the sodium line.¹ Raman lasers work by stimulated scattering rather than stimulated emission. The researchers found that this core difference enables the laser to operate more stably at a pure single frequency.

The laser delivered higher power and efficiency than previous guide-star laser systems of its particular type; its characteristics are already competitive with other approaches, but the real significance of the result, say the researchers, is that the technology can be further developed to increase the quality of future guide stars.

Good power scaling

Diamond can dissipate heat rapidly, and is less prone to unwanted optical distortions. This combination provides a pathway towards producing more-powerful guide-star beams. The researchers predict that its extra flexibilities, such as delivering the laser power as a series of microsecond optical pulses, will be a benefit for AO systems. As well as power scaling, the diamond sodium laser concept is promising for generating microsecond-duration pulsed output with simultaneous high peak power and average power, to enable more point-like guide stars to be generated through AO systems, and other enhancements, according to the researchers.

“Our approach is also highly practical, because as the intrinsic gain properties of the diamond element mean the laser is found to run on a single narrow frequency,” says Dr Xuezong Yang, lead experimentalist on the project. “This keeps our design simple, and the device potentially robust and low-cost.”

“We believe that the diamond approach will provide an interesting system for greatly expanding the brightness and quality of future guide stars,” says Rich Mildren, research leader for the work. “The light-atom interaction in the sodium layer happens to be extremely complex, but this brings forth interesting opportunities to adapt lasers to boost the performance of earth-to-space adaptive optical systems.”

Source: https://www.scimex.org/newsfeed/a-diamond-laser-makes-guiding-stars

REFERENCE:

1. Xuezong Yang et al., Optics Letters (2020); https://doi.org/10.1364/OL.387879.

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.