Guide Stars are used to light up the sodium layer 90 kilometers up in the atmosphere in order to create an artificial star - used to improve telescopic images. To combat atmospheric distortion, which causes blurred images, a deformable mirror is integrated in the telescope. A wavefront sensor is used to collect information as to how the atmosphere is affecting light from the star, and real-time corrections are computed to manipulate the hundreds of planes on the mirror to negate the distortion – adaptive optics. Real stars can be used, but they have to be bright and close to where the telescope is pointed. Creating artificial stars on demand opens up a whole new universe of photographic possibilities, while delivering images with much greater sharpness than previously possible.

In this “next generation” Guide Star, narrow-band 1178-nm emission from a 25-mW diode laser is amplified to the 40-W level and then frequency doubled in a resonant cavity doubler to provide 22 W at the desired sodium resonance wavelength of 589 nm. The novel technology developed to achieve such high power amplification of an extremely narrow-band seed is the polarization-maintaining (PM) Raman fiber amplifier (RFA) developed by MPB Communications Inc.

The unique design of MPB Communications’ RFA pump laser allows the compact laserhead (containing the RFA and doubler stage) and the larger electronics cabinet (containing the pump laser, seed laser, power supply and other electronic modules) to be mounted either directly on the Nasmyth platform of the telescope or up to 27 m apart, thereby providing unprecedented flexibility for installation on telescopes.

Installations

• 4LGSF (Four Laser Guide Star Facility), Paranal, Chile

• KECK, Mauna Kea, Hawai'i

• Gemini North, Mauna Kea

• Gemini South, Cerro Pachón, Chile

• Subaru, Mauna Kea, Hawai'i (pending)

Partners

Patented ESO technology was licensed to MPB Communications Inc. and Toptica Germany, who collaboarted together to manufacture the Laser Guide Stars.

MPB Contribution

MPBC provided the novel narrow-band, polarization-maintaining Raman fiber amplifiers used to amplify the output of a Toptica narrow-band laser diode at 1178 nm which is then converted to 589 nm by a resonantly-enhanced high-power frequency doubler from Toptica.

Awards

• The Berthold Leibinger Innovationspreis

• OSA's 2017 Paul F. Forman Team Engineering Excellence Award

Papers

• Series production of next-generation guide-star lasers at TOPTICA and MPBC, Martin Enderlein,  Axel Friedenauer, Robin Schwerdt,  Paul Rehme,  Bernhard Ernstberger, Patrick Leisching, Wilhelm G. Kaenders (TOPTICA), Wallace R. L. Clements,  Daoping Wei, Vladimir Karpov (MPB Communications Inc.) - SPIE Adaptive Optics Systems, 2014