Light Sabers on Mauna Kea
June 6, 2011
What?s old is new again. First the old: The iconic sci-fi image of port and starboard phasers firing on a hostile foe, as seen from the bridge of the starship Enterprise. And here?s what makes it new again: a strikingly similar image (minus the enemy spacecraft) caught by photographer and Keck electronics engineer Andrew Cooper several weeks ago on Mauna Kea.
Cooper was not on the bridge of any starship, but outside the Keck domes, battling a frigid gale to catch the very first images of both Keck Observatory telescopes launching lasers at the same time. It was a test of the Keck I laser, which is a more powerful version of what has been on the Keck II telescope for years. The new laser brings the total to four laser systems in operation on Mauna Kea: one on each Keck telescope, one on the Subaru Telescope and one on the Gemini North telescope.
The purpose of all these lasers is to help astronomers study distant objects in space, of course. An unexpected benefit is a stream of stunning new images of what is taking place at the observatories themselves. On May 26 lasers on both Keck telescopes and the Subaru were on at the same time, leading to more amazing photographs by both Cooper and Subaru Telescope?s Dan Birchall. Both of these dogged astro-photographers also created dramatic movies of the events which can be found via the Keck Observatory website: keckobservatory.org.
A (Guide) Star is Born
There?s far more to the story than just the fantastic images, however. There is the new Keck I laser itself. It?s a different animal than the laser on its twin, the Keck II telescope, and is the ?next generation? of the most dynamic area of modern astronomy.
The Keck II laser has been in operation since its ?first light? December, 2001. It has been in science operation since July 2004. It was the pioneer that set the standard for all large telescope lasers currently in operation. The Keck II laser is what?s called a sodium dye laser, the beam from which is launched through a long trumpet-like tube bolted to the side of the Keck II telescope structure. Like all of the telescope lasers, its purpose is to charge up a layer of sodium atoms left by vaporized meteors (a.k.a. shooting stars) in a layer of Earth?s atmosphere 60 miles above the ground. When the laser hits these sodium atoms they light up and create what serves as an artificial star, or Laser Guide Star, as it?s called in the business.
Why make a fake star? The Earth?s atmosphere makes stars twinkle and distorts their images, limiting some astronomers? observations. With information from the Laser Guide Star astronomers can automatically correct for these distortions ? literally taking the twinkle out of the stars ? using a deformable mirror that changes it shape at a rate of up to 2,000 times per second ? a system called Adaptive Optics. The results are crisp images of celestial objects that are better than most images obtained from space telescopes.
Free Space Transport
Now it?s Keck I?s turn. Despite being the older of the twin telescopes, Keck I is now equipped with the newer, more powerful solid state laser that is launched into the night sky through the center of the telescope via a complex series of mirrors. These mirrors make up what the engineers call the ?Free Space Transport? system for the laser beam (which ? in case you?re wondering ? has absolutely nothing in common with the space transporters on Star Trek). The result is more power to those high-altitude sodium atoms and a brighter Laser Guide Star.
?We now have twice the output power,? said Jason Chin, the Keck Observatory engineer overseeing the installation of the new laser system. Launching the laser from the center of the telescope instead of the side is also better because it creates a tighter Laser Guide Star, Chin explained.
Chin and his team are now working on the last few adjustments to the new laser system to make it ready for use by astronomers. The biggest of those is fully factoring in the flexing of the giant 300-ton telescope itself.
?Nothing that big is totally stiff,? Chin explained. And something that big being moved up and down and around in circles to aim at different parts of the sky is bound to flex in ways that can change the laser beam?s path through all those mirrors. It?s an interesting problem that Chin is totally confident they will lick.
Seven More Laser Beacons
The new Keck I laser is not the end of the story, however. Like all single laser guide star systems, it suffers from one major limitation: it only allows astronomers to correct distortions in a very small patch of the sky. The Next Generation Adaptive Optics now being developed for Keck Observatory will employ no less than seven laser beacons. The idea is to correct for the atmospheric distortions in the full cylinder of atmosphere above the telescope mirror over a larger patch of sky, which will allow for even sharper images.
If this has whetted your appetite about lasers or other happenings at Keck Observatory, you are in luck: On Thursday, June 23 at 7 pm, Keck Observatory Director Taft Armandroff will be giving a free public lecture at Keck headquarters in Waimea as part of the monthly Astronomy Lecture Series. To sign up for regular notices of lectures and other Keck events, join the Keck Nation mailing list or come by the Keck headquarters Visitor Center and sign up in person.