A robust new laser will enhance the adaptive optics

In some applications, bigger lasers mean better lasers. That’s the case in astronomy, where lasers are used for everything from telescope calibration to satellite communications. The European Southern Observatory (ESO) and some of its commercial partners have developed a laser that is three times more powerful than the existing industry standard. With this increased performance, the new system has the potential to dramatically improve the way telescopes deal with one of the most fundamental problems in ground-based astronomy – atmospheric turbulence.

Regular atmospheric turbulence is commonplace on Earth and is the cause of what the human eye perceives as the “twinkling” of the stars. For a telescope, however, turbulence that is not taken into account can lead to entire data sets being thrown out. Telescopes have a standard technique for eliminating such effects – they calibrate with a known stable star.

UT video explaining atmospheric turbulence.

The obvious problem is that sometimes there aren’t any stars to calibrate to. So the scientists devised a way to build an “artificial star” that would allow observatories to calibrate against a stable observable object, no matter which direction they are facing. In this technique, sodium atoms are blasted 90 km high into the atmosphere with a laser.

Today this technology exists as the Four Laser Guide Star Facility, which operates ESO’s Very Large Telescope (VLT). With an output of a respectable 22W, this calibration tool was critical to the successful operation of the VLT. However, the more the laser acts on the sodium atoms, the more stable the calibration “star” is. So ESO has increased the power to 63 W – almost three times as much as the existing system.

This wide-field image shows the CaNaPy laser that is being tested in the sky of the Allgäu public observatory in Ottobeuren in Germany. The laser, based on a technology patented by ESO, excites sodium atoms in the upper atmosphere and creates an artificial source that can be used to monitor and correct atmospheric turbulence. This laser will eventually be installed in the European Space Agency (ESA) optical ground station in Tenerife, Spain as part of a collaboration between ESO and ESA to use adaptive optics for astronomical and satellite communications purposes.
Credit – ESO

This increase is due to the development of an advanced Raman fiber amplifier laser source developed by MPB Communications – a Canadian company that acts as one of ESO’s commercial partners. You weren’t alone in developing technologies to improve calibration lasers. TOPTICA Photonics Ag is a German company that specializes in the manufacture of frequency chirping systems that allow the laser to jump back and forth between multiple frequencies. Larger bandwidths mean more excited sodium atoms and a bright star for calibration.

Calibration isn’t the only thing the improved lasers are useful for, however. Satellite communication systems have become much more important lately, with SpaceX’s Starlink ushering in a new era in space-based communications. However, they are limited in their use of one of the fastest data transfer techniques. Optical communication between satellites and the earth itself is hampered by the same atmospheric turbulence phenomena that can throw telescopes off track. Because this higher powered laser is able to create more stable calibration points for these systems, optical communication becomes a much more attractive data transfer method.

This picture shows the 57W CaNaPy laser during a field test on the 0.6 m telescope at the Allgäuer VolksSternwarte Ottobeuren in Germany. The laser light travels from the inside of the telescope to its secondary mirror and bounces back to the main mirror, where it is eventually reflected towards the sky. The laser, which is based on the technology patented by ESO, will ultimately be part of the CaNaPy Laser Guide Star adaptive optics system, which is to be operated in the optical ground station of the European Space Agency in Tenerife, Spain. It will help correct astronomical observations for the blurring effect caused by turbulence in the earth’s atmosphere.
Credit – ESO

Scientists plan to install the new laser system, which is part of the CaNaPy Laser Guide Star adaptive optics system, at an ESA observatory in Tenerife, Spain. When the system proves itself, it can serve as the basis for other improved calibration and communication tools in the expanding observation and network platforms around the world.

Learn more:
ESO – New powerful laser based on ESO technology passes field test
SPIE – CaNaPy: SatComm LGS-AO experimental platform with laser uplink precompensation
Novus Light – powerful new laser passes field test
UT – artificial star shines in the southern sky

Mission statement:
CaNaPy laser tested in Germany.
Credit – ESO

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