Search Menu
Photonics Media Photonics Buyers' Guide Photonics EDU Photonics Spectra BioPhotonics EuroPhotonics Industrial Photonics Photonics Showcase Photonics ProdSpec Photonics Handbook
More News
Email Facebook Twitter Google+ LinkedIn Comments

Laser Takes the Twinkle out of Starlight
May 2002
LONG BEACH, Calif., May 22 -- Stars twinkle because of disturbances in the atmosphere blanketing our planet. Although the effect inspired a well-known nursery rhyme, it hampers astronomers' attempts to study many heavenly bodies.
   A group at Lawrence Livermore National Laboratory has now developed a system, known as a sodium guide star, that allows astronomers to accurately account for atmospheric disturbances and produce much clearer stellar images. Deanna Pennington, a physicist in the lab's laser program, described their research during a press conference yesterday at CLEO/QELS 2002.
   The guide star consists of a laser that illuminates sodium atoms in an atmospheric layer 60 miles above the earth, producing a small, bright spot of light high in the sky. By aiming the laser at a portion of the sky near a star of interest and measuring fluctuations in the guide star's light, astronomers can monitor atmospheric distortions wherever they choose to point their telescopes.The Konstanz-Düsseldorf team made use of two devices known as "optical cavities" pointing in different directions. Such cavities basically consist of two mirrors held at a constant distance. The round-trip time of a light beam between the mirrors is a direct measure of the speed of light perpendicular to the mirror surfaces. Any dependence of this speed on the direction of space would show up when the setup is rotated. However, errors creep in through variations of the cavity length, caused by temperature effects and material aging processes. Thus, the researchers employed cavities made from an ultra-pure sapphire crystal, which is virtually impervious to aging effects, and operated it at the temperature of liquid helium, near absolute zero. Length changes are thus reduced to a level significantly lower than what can be achieved at room temperature. Using advanced laser techniques for reading out the cavity round-trip time, the team could obtain a new limit on possible violations of light propagation isotropy.

Laser Takes the Twinkle out of Starlightlasers

Terms & Conditions Privacy Policy About Us Contact Us
back to top
Facebook Twitter Instagram LinkedIn YouTube RSS
©2018 Photonics Media, 100 West St., Pittsfield, MA, 01201 USA,

Photonics Media, Laurin Publishing
x We deliver – right to your inbox. Subscribe FREE to our newsletters.
We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.