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Mededeling

New powerful laser based on ESO technology passes field test

31 augustus 2021

A powerful experimental laser, based on ESO technology, passed a key test last month at the Allgäuer VolksSternwarte Ottobeuren observatory in Germany. The adaptive-optics laser, developed in collaboration with industry, has important additional capabilities compared to existing systems. It will be part of the CaNaPy Laser Guide Star Adaptive Optics system set to be installed at the European Space Agency’s (ESA) Optical Ground Station in Tenerife, Spain, in the frame of the ESO–ESA Research & Development collaboration. The higher laser power, nearly three times higher than in current systems, opens the door for developments in laser satellite communication, as well as significant improvements in the sharpness of astronomical images taken with ground-based telescopes.

Astronomical adaptive optics refers to systems on ground-based telescopes that correct for the blurring effect brought about by turbulence in the Earth’s atmosphere — the same effect that causes stars seen from Earth to “twinkle”. To remove the distortions, these systems require a bright reference star close to the object of study. Because these stars are not always conveniently placed on the sky, astronomers use lasers to excite sodium atoms at 90 km altitude in the Earth's atmosphere, creating artificial stars near the field of interest that can be used to map and correct the atmospheric turbulence.

The new experimental laser is based on the same ESO technology that is behind the Four Laser Guide Star Facility, successfully operating at ESO’s Very Large Telescope in Chile, as well as at most large astronomical observatories in the world. But while those lasers have a power of 22 Watts, this new laser has almost tripled the power at 63 Watts, a huge leap forward in astronomy laser technology that will, among other things, improve the sharpness of adaptive-optics images at visible wavelengths. As part of a collaborative R&D agreement with ESO, the Canadian company MPB Communications — one of ESO’s industry partners — has been able to scale up the power of their infrared “Raman fibre amplifier” source. This is the breakthrough that allows the ESO CaNaPy laser to achieve such a high power [1].

In addition, the German company TOPTICA Photonics AG, another of ESO’s industry partners, has developed and implemented in the CaNaPy laser a frequency chirping system for this new class of lasers, as part of a collaborative R&D agreement with ESO. Chirping consists in rapidly changing the frequency to which the laser is tuned. This increases the number of sodium atoms excited by the laser, making the artificial star brighter and thus improving the turbulence correction. TOPTICA has installed the chirping prototype on the 63 Watts laser and, with ESO, has commissioned on sky both the laser and its novel chirping system.

This new experimental CaNaPy laser is an example of astronomical technology developed in-house at ESO, in partnership with industry, and then transferred back to industrial usage including in new fields, thus finding applications beyond its original purpose and benefitting society as a whole. Once the CaNaPy facility instrument is installed at the ESA Optical Ground Station in Tenerife — a collaborative project between ESO [2] and ESA — it will provide both organisations, ESA and ESO, with opportunities to advance the use of laser guide star adaptive optics technologies not only for astronomy but also for satellite optical communication. Optical laser communication allows satellites to send and receive signals to and from Earth with ultra-fast bandwidth, a prospect that ESA is investigating. Optical laser signals can transmit much more information than radio signals, but they are equally affected by atmospheric turbulence. Laser guide star adaptive optics has thus the potential to greatly improve the optical links between satellites and ground stations.

Notes

[1] MPB Communications scaled up the power of their Raman fibre amplifier, which operates in the infrared at 1178 nm, from the 36 Watts level normally used in the commercial sodium guidestar lasers, to an unprecedented level of 100 Watts. This allows CaNaPy to achieve a continuous-wave power of 63 Watts while operating at 589 nm, in the visible.

[2] The collaboration includes several institutes in ESO member states: the Istituto Nazionale di Astrofisica in Italy, Durham University in the UK, and the Instituto de Astrofísica de Canarias in Spain.