The next generation of adaptive optics has arrived at the Large Binocular Telescope (LBT) in Arizona, providing astronomers with a new level of image sharpness never before seen. Developed in a collaboration between Italy’s Arcetri Observatory of the Istituto Nazionale di Astrofisica (INAF) and the
University of Arizona’s Steward Observatory, this technology represents a remarkable step forward for astronomy.
Until relatively recently, ground-based telescopes had to live with wavefront distortion caused by the Earth’s atmosphere that significantly blurred the images of distant objects (this is why stars appear to twinkle to the human eye). While there have been advancements in adaptive optics technology to correct atmospheric blurring, the LBT’s innovative system truly takes this concept to a whole new level.
In closed-dome tests beginning May 12 and sky tests every night since May 25, astronomer Simone Esposito
and his INAF team tested the new device, achieving exceptional results. The LBT’s adaptive optics system,
called the First Light Adaptive Optics system (FLAO), immediately outperformed all other comparable systems,
delivering an image quality greater than three times sharper than the Hubble Space Telescope using just one
of the LBT’s two 8.4 meter mirrors. When the adaptive optics are in place for both mirrors and their light is
combined appropriately, it is expected that the LBT will achieve image sharpness ten times that of the Hubble.
“This is an incredibly exciting time as this new adaptive optics system allows us to achieve our potential as the
world’s most powerful optical telescope,” said Richard Green, Director of the LBT. “The successful results
show that the next generation of astronomy has arrived, while providing a glimpse of the awesome potential
the LBT will be capable of for years to come.”
Remarkable Test Results Set New Standard for Optical Astronomy
The unit of measure for perfection of image quality is known as the Strehl Ratio, with a ratio of 100%
equivalent to an absolutely perfect image. Without adaptive optics, the ratio for ground-based telescopes is
less than 1 percent. The adaptive optics systems on other major telescopes today improve image quality up to
about 30 percent to 50 percent in the near-infrared wavelengths where the testing was conducted.
In the initial testing phase, the LBT’s adaptive optics system has been able to achieve unprecedented Strehl
Ratios of 60 to 80 percent, a nearly two-thirds improvement in image sharpness over other existing systems.
The results exceeded all expectations and were so precise the testing team had difficulty believing their
findings. However, testing has continued since the system was first put on the sky on May 25, the LBT’s
adaptive optics have functioned flawlessly and have achieved peak Strehl Ratios of 82 to 84 percent.
“The results on the first night were so extraordinary that we thought it might be a fluke, but every night since
then the adaptive optics have continued to exceed all expectations. These results were achieved using only
one of LBT’s mirrors. Imagine the potential when we have adaptive optics on both of LBT’s giant eyes.” said
Simone Esposito, leader of the INAF testing team.
Image one: A picture of the movable secondary mirror during its installation in the Arcetri lab. The image shows
the 672 tiny magnets spread over the back of the mirror. The reflecting face of the mirror is face down. The
upper portion contains the electro-mechanical devices that control the magnets. (Photo by R. Cerisola)
Image two: A double star as observed with the LBT in standard mode (left), and with the adaptive
correction activated (right). Because of atmospheric blurring, the fainter companion of the star cannot be
identified in the images taken in standard mode, while it is easily visible when the adaptive module is
activated. A third faint star also becomes visible in the upper right part of the frame, thanks to the increased
sensitivity of the telescope in adaptive mode.
More images from the adaptive optics system are available at www.lbto.org.
A Decade of Effort Delivers Technological Triumph Development of the LBT’s adaptive optics system took more than a decade through an international
collaboration. INAF, in particular the Arcetri Observatory, conceived the LBT instrument design and developed
the electro-mechanical system, while the University of Arizona Mirror Lab created the optical elements, and the
Italian companies Microgate and ADS International engineered several components. A prototype system was
previously installed on the Multiple Mirror Telescope (MMT) at Mt. Hopkins, Ariz. The MMT system uses
roughly half the number of actuators as the LBT’s final version, but demonstrated the viability of the design.
The LBT’s infrared test camera, which produced the accompanying images, was a joint development of INAF,
Bologna and the MPIA, Heidelberg.
“This has been a tremendous success for INAF and all of the partners in the LBT,” said Piero Salinari,
Research Director at the Arcetri Observatory, INAF. “After more than a decade and with so much care and
effort having gone into this project, it is really rewarding to see it succeed so astoundingly.”
This outstanding success was achieved through the combination of several innovative technologies. The first is
the secondary mirror, which was designed from the start to be a main component of the LBT rather than an
additional element as on other telescopes. The concave secondary mirror is 0.91 meters in diameter (3 feet)
and only 1.6 millimeters thick. The mirror is so thin and pliable that it can easily be manipulated by actuators
pushing on 672 tiny magnets glued to the back of the mirror, a configuration which offers far greater flexibility
and accuracy than previous systems on other telescopes. An innovative “pyramid” sensor detects atmospheric
distortions and manipulates the mirror in real time to cancel out the blurring, allowing the telescope to literally
see as clearly as if there were no atmosphere. Incredibly, the mirror is capable of making adjustments every
one thousandth of a second, with accuracy to better than ten nanometers (a nanometer is one millionth the
size of a millimeter).
More on LBT The $120 million LBT on Mount Graham utilizes two giant 8.4 meter mirrors and with the new adaptive optics
the telescope will achieve the resolution of a 22.8-meter, or approximately 75-foot telescope. Implementation of
the adaptive optics is the latest of several major breakthroughs for the LBT in recent months. For example, in
April a near-infrared camera/spectrograph developed by a consortium of German institutes became available
to astronomers for scientific observations, allowing them to penetrate interstellar dust clouds and reveal the
secrets of the youngest and most distant galaxies. The new adaptive optics will enable other such versatile
instruments to achieve their full potential on the LBT.
The LBT is an international collaboration among institutions in the United States, Italy and Germany.
The LBT Corporation partners are:
• The University of Arizona on behalf of the Arizona university system
• Istituto Nazionale di Astrofisica, Italy
• LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the
Astrophysical Institute Potsdam, and Heidelberg University
• The Ohio State University
• The Research Corporation, on behalf of The University of Notre Dame, University of
Minnesota and University of Virginia