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China Takes Leadership Role in TMT Laser Guide Star Facility

02.24.2012

Corinne Boyer, TMT Observatory Corporation

During the last twelve months, TMT collaborators in China have made significant progress on the design of the Laser Guide Star Facility (LGSF) for TMT. Carried out by Dr. Kai Wei and his team, the Institute of Optics and Electronics (IOE) in Chengdu (China) has taken the lead for the design of the beam transfer optics and laser launch telescope sub-system. They recently updated the conceptual design originally developed by the National Optical Astronomy Observatory (NOAO) to adapt for changes in the telescope design and to include new requirements.

The updated conceptual design was successfully reviewed on June 22, 2011 in Beijing by a group of experts from other observatories including Maxime Boccas (Gemini), Jason Chin (Keck) and Scott Roberts (HIA).

Another very important activity, carried out by TMT colleagues in China at the Technical Institute of Physics and Chemistry (TIPC) in Beijing, is the design, development and test of a 20W prototype sodium laser for TMT. The team at TIPC led by Dr. Yong Bo has refurbished their bench prototype into a field prototype that was tested on-the-sky during the spring of 2011 at the 1.8m telescope in Yunnan in collaboration with IOE.

A review of the TIPC work was organized after the IOE review on June 23–24, 2011 in Beijing. The review committee was composed of a group of renowned laser experts from the US and other observatories including: Roger Falcone (ALS), Roger Barty (LLNL) and Jason Chin (Keck). The laser prototype was brought back from Yunnan for display and operation at the review requiring a non-stop 3000 kilometer five day road trip.

What is the Laser Guide Star Facility?

The LGSF is the system that generates and projects onto the sky the laser guide star (or artificial guide star) constellations needed by first light and future generations of Adaptive Optics (AO) systems (See the Project Manager’s Corner: Making Your Own Stars in the March 2011 issue of Segments). The TMT first light AO system will use a constellation of six laser guide stars, which in combination with multiple deformable mirrors will enable full diffraction-limited imaging in the near infrared over a large field of view.

The LGSF consists of three main systems: the laser system that generates the sodium laser beams, composed of six 20 to 25W sodium lasers; the beam transfer optics and laser launch telescope system, which transports the laser beams using mirrors and relay lenses and then projects the laser beams from a laser launch telescope located behind the TMT secondary mirror; and the laser safety system, which ensures the lasers are operated safely.

The Institute of Optics and Electronics has recently supported the development and operations of a laser guide star system for the GaoMeigu 1.8m telescope located in the province of Yunnan (China).

Work is continuing now at IOE and TIPC, with more design and prototyping efforts scheduled for the next 12 months. China is taking a leadership role in the design, and development of the TMT LGSF.