Adaptive Optics

• The Shane Telescope using the Adaptive Optics (AO) system with a laser guidestar. Photo by Laurie Hatch.

Adaptive optics (AO) is an enormous new area of interest throughout the world.

AO provides a clearer view of the universe by compensating for atmospheric turbulence that causes stars to "twinkle."

The adaptive optics adjustment is made with a deformable mirror that is almost infinitely adjustable. It changes shape in numerous places hundreds of times per second, compensating for changing atmospheric conditions to focus light precisely. Essentially, when a celestial object is to be observed, a fairly bright star nearby is monitored, and a correction is made for the "twinkle" that is observed. This correction is then applied to the object when it is observed.

Some highlights:

• Adaptive Optics (AO) has enabled atmospheric observations of planets and satellites within our solar system, including Neptune's weather and the atmosphere of Titan.
• Active galaxies have black holes in their centers that are actively consuming gases and emitting x-rays. Using adaptive optics, Lick astronomers can study two types of active galaxies.
• Observations of asteroids indicate that some asteroids are actually double. With AO, these objects are resolved into two separate images.
• Quasars are very distant and massive active galaxies that emit visible light, x-rays and radio waves. Using AO, researchers now observe quasar spectra.
• Seyfert galaxies visible and infrared light, x-rays, and radio waves. Through direct imaging, AO is beginning to reveal the inner environment adjacent to the black hole, as well as the surrounding galaxtic structure.

Lick Laser Guide Star System

Did you know that Lick Observatory astronomers and scientists from Lawrence Livermore National Labs engineered the world’s first laser guide star system routinely used for science?

A natural guide star is not always present near the object that astronomers want to observe. By shooting a laser beam into the sky near the object to be observed, astronomers create an artificial "star" of glowing atmospheric sodium ions. This laser guide star functions like a natural guide star, providing correct focus for the object being observed.

How does it work?

In the video, a sodium laser and its launch telescope are attached to the side of the Shane telescope tube and project a laser beam up to the mesosphere (about 90 kilometers above the ground) where it illuminates a layer of neutral sodium atoms left behind by meteorites decaying as they enter the atmosphere.

The yellow-colored laser beam is tuned to a specific wavelength of light that excites those sodium atoms, producing a relatively bright artificial star that the AO system uses to measure the instantaneous turbulence in the Earth's atmosphere. The AO system then uses that measurement to rapidly adjust a deformable mirror which is used to counteract the turbulence and thereby produce a much sharper image of the astronomical object being observed.