The ground-layer adaptive optics system, or GLAS, works with a high-tech pulsed laser. The laser beam is projected from a small telescope mounted behind the secondary mirror of the William Herschel Telescope, producing an artificial star in the sky at an altitude of 15 kilometres. The light coming from the artificial star is detected by a sensor that measures the atmospheric distortions.
This information is used at a rate of several hundred times per second to shape a rapidly adjustable deformable mirror to take out the adverse effects of atmospheric turbulence. The somewhat low altitude of the artificial star implies that air turbulence nearer the ground is preferentially illuminated and corrected, and therefore it is usually referred to as ground-layer adaptive optics.
The importance of such a laser adaptive optics system goes beyond the immediate scientific interests at the William Herschel Telescope. Scientists are currently developing future extremely large telescopes that will have mirror diameters of thirty or even forty meters. These future huge telescopes will have to rely on adaptive optics with lasers, and correction of ground-layer turbulence will be of crucial importance.
This project was made possible through a grant from the Division for Physical Sciences of the Netherlands Organisation for Scientific Research, with assistance from the OPTICON network funded by the European Union.
The William Herschel Telescope is part of the Isaac Newton Group of Telescopes (ING). The ING is owned and operated jointly by the Science and Technology Facilities Council (STFC) of the United Kingdom, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands and the Instituto de Astrofísica de Canarias (IAC) of Spain. The telescope is located in the Spanish Observatorio del Roque de los Muchachos on La Palma, Canary Islands, Spain. The international observatory is operated by the Instituto de Astrofísica de Canarias (IAC).
Even the biggest and best astronomical telescopes on the highest mountains and under pristine clear skies are hampered by the Earth’s atmosphere in their endeavour to look sharply into the cosmos. Subtle variations of air temperature cause the starlight to become distorted before it reaches the telescope. There, the rapidly changing distortions result in images from far away stars and galaxies becoming blurred, which poses a severe restriction on the capability of telescopes on the ground.
To counteract the disturbing effect of the earth’s atmosphere, scientists and engineers have developed techniques that allow them to measure and correct for the atmospheric distortions in an attempt to try to recover a perfectly sharp picture. A small mirror whose shape can be rapidly adjusted corrects for the atmospheric distortions. This technique is referred to as adaptive optics and is being used at a number of telescopes around the world, including the 4.2-m William Herschel Telescope on the island of La Palma, in the Canary Islands.
Although adaptive optics has been in operation on a regular basis for some years, the real benefits for astronomical research can only be unleashed when the technique is used in conjunction with a laser beam that generates a point source of light in the sky. This point, or artificial star, can then be used to measure the distortions caused by the Earth’s atmosphere. Without such a laser only a very small fraction of the sky can be studied, while with a laser nearly the full sky is available for scientific studies. This provides a remarkable advantage for astronomers.
It is not customary to see artificial lights at an astronomical observatory at night. Lights in general badly affect professional telescopes. The laser light used here, however, does not affect the observations because it is very well focused and works at only one very specific colour. Moreover, a system has been implemented that coordinates where all telescopes are pointing and prevents the laser from adversely affecting other telescopes.
The laser beam is only visible by the unaided eye from close to the telescope building. Time exposures clearly show the green laser beam coming from the telescope. The artificial star that the laser produces is much too faint to be seen by the unaided eye, but is of course bright enough to be seen with the telescope.
Javier Méndez | alfa
UNH scientists help provide first-ever views of elusive energy explosion
16.11.2018 | University of New Hampshire
NASA keeps watch over space explosions
16.11.2018 | NASA/Goddard Space Flight Center
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
16.11.2018 | Health and Medicine
16.11.2018 | Life Sciences
16.11.2018 | Life Sciences