Click to listen to an episode of the 365 Days of Astronomy podcast from September 9th, 2009. Its an interview with an adaptive optics scientist searching for extrasolar planets.
adaptive optics
Lasers in Astronomy
There are no two ways about it: lasers are cool. Their intense, highly-controlled beams allow physicists to heat up matter, to cool down matter, and much more. In astronomy, lasers allow for precise lunar ranging experiments, and are quickly allowing ground-based telescopes to rival the resolution of the Hubble Space Telescope.
The concept of the space telescope is simple: put the telescope in orbit in order to avoid distortion of the light from beyond the atmosphere. Of course, getting a telescope into orbit is expensive, and maintaining it while it is there requires the Space Shuttle and astronauts who can work in orbit. Its a much more complex endeavor than building an observatory on a mountaintop.
Mountaintop observatories like the Gemini telescope and Keck can now use lasers to create artificial ‘guide stars’. Astronomers energize the upper atmosphere with a laser beam causing a small spot in the sky to glow like a star. The light from that glow is then studied for atmosphere-induced distortions when it enters the telescope. Electronics in the telescope then quickly deform an optical surface in the pathway of the light to exactly counteract the distortions present from the atmosphere (at 2:20 in the video). This so-called ‘adaptive optics’ can effectively cancel out the blurring effects of the atmosphere. The video below (from the Gemini observatory) outlines this process.
A fantastic NOVA special PBS chronicles the search for a supermassive black hole at the center of the Milky Way- and the technical challenges that were overcome as that search came to fruition. Here is a very good segment on adaptive optics, you can watch the entire episode here.
Spurious laser beams into space from Earth could be beacons from us to a curious alien civilization- at least, this is an idea that inspires the Optical SETI program.
At Mauna Kea, the two Keck telescopes have to avoid shining their laser systems while the other is imaging- hence the ‘first on laser policy‘.
Cahall Observatory 