Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Laser beams help take the twinkle out of starlight

04.06.2002


If you have ever peered down a highway on a sunny day, you have probably seen the rising, wavelike ripples of heated air that distort the appearance of objects near the horizon. Similar disturbances in the atmosphere above us make stars twinkle as their light is distorted on the way down to Earth.



Although twinkling stars inspired a well-known nursery rhyme, the effect hampers astronomers’ attempts to study the heavens. Scientists at Lawrence Livermore National Laboratory are now building systems, known as a synthetic guide stars, to help astronomers accurately account for atmospheric distortions wherever they choose to point their telescopes. Pictures collected by large terrestrial telescopes equipped with such systems often exceed the quality of Hubble Space Telescope images.

Guide stars have long played an important role in correcting atmospheric distortion. Astronomers pick a bright, stable star near a region of the sky that they hope to study and monitor distortions in the guide star image to deduce the optical properties of the atmosphere. They then correct their images with adaptive optics, which distort telescope components to offset atmospherically induced errors. Generally, adaptive optics corrections involve warping light-collecting telescope mirrors with computer controlled motors that respond to changes in the guide star image.


Guide stars and adaptive optics combine to provide stunning pictures of planets, galaxies, and other objects. Unfortunately, astronomers find suitable natural guide stars in only one percent of the sky. At the 2002 Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference (May 19-23, www.cleoconference.org) meeting in Long Beach, CA, Deanna Pennington explained that she and her colleagues at Lawrence Livermore National Laboratory have now opened up a much larger portion of the heavens with a manmade analog to guide stars. Pennington estimates that the synthetic guide star system can correct for atmospheric turbulence in about three fifths of the sky.

The researchers create their synthetic guide star by beaming a laser through the atmosphere in the direction of an object they wish to study. The frequency of the laser is specifically chosen to excite sodium atoms, causing them to emit yellow light. Sodium is relatively scarce in most of our atmosphere, but incoming meteors deposit a concentrated layer of the atoms in the mesosphere, about ninety kilometers above the earth. The laser paints an artificial star in the sky when it strikes the sodium rich layer.

Pennington points out that natural stars are best for correcting atmospheric distortion. Stars are so far away that they appear to be point light sources effectively located at infinity. Synthetic guide stars, in comparison, are too close to completely eliminate atmospheric errors, but they provide astronomers with seventy-five percent of the benefit offered by natural guide stars.

Any telescope equipped with adaptive optics can benefit from the addition of a synthetic guide star system, but the technology will be indispensable for future, earth-based observations. "Very large telescopes," says Pennington," must use adaptive optics to approach their theoretical performance. Atmospheric turbulence primarily dictates the ultimate resolution a telescope can achieve." Telescope designs being considered for future observatories may sport mirrors thirty to a hundred meters across, and will dwarf even cutting-edge telescopes such as the ten-meter telescope at Keck Observatory in Hawaii. Larger telescopes collect more light and could provide ever high resolution images, provided we correct for the hazy blanket of gas that surrounds our planet.

Although the Keck telescope already uses adaptive optics that rely on natural guide stars, Pennington’s group installed a new sodium guide star system at the observatory last year. Keck’s adaptive optics successfully locked on to the laser-generated guide star in tests performed last December, but modifications to the system interfaces prevented astronomers from using it to collect images. If the final installation stages go as planned, a synthetic guide star shining over Hawaii should help astronomers peer into the heavens by Christmas 2002.

For more information contact:

Deanna Pennington pennington1@llnl.gov
Lawrence Livermore National Laboratory
P.O. Box 5500, L-477
Livermore, CA 94551
925-423-9234


James Riordon | EurekAlert

More articles from Physics and Astronomy:

nachricht A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne

nachricht Quantum thermometer or optical refrigerator?
23.06.2017 | National Institute of Standards and Technology (NIST)

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>