Published on Apr 02, 2024
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Adaptive Optics in Ground Based Telescopes
Introduction
==> Adaptive optics is a new technology which in effect removes this atmospheric tremor and helps the astronomers see the images through earth based telescopes more brightly
==> Without using this system, the images obtained through telescopes on earth are seen to be blurred, which is caused by the turbulent mixing of air at different temperatures
==> It brings together the latest in computers, material science, electronic detectors, and digital control in a system that warps and bends a mirror in a telescope to counteract, in real time the atmospheric distortion
What Is Adaptive Optics ?
==> Adaptive optics refers to optical systems which adapt to compensate for optical effects introduced by the medium between the object and its image
==> In order to avoid atmospheric aberration, one can turn to larger telescopes on the ground, which have been equipped with ADAPTIVE OPTICS system.
==> With this setup, the image quality that can be recovered is close to that the telescope would deliver if it were in space.
==> Images obtained from the adaptive optics system on the 6.5 m diameter telescope, called the MMT telescope illustrate the impact
Basic Principle
==> An adaptive optics system reflattens the wave fronts by reflecting the light of a deformable mirror whose shape is changed in real time to introduce an equal but opposite distortion
==> The information on how to distort the mirror comes from a wave front sensor, an instrument that measures optical aberration imposed by the atmosphere on light from a star.
==> After the light reflects of the deformable mirror, a beam splitter sends part of the light to a camera that will capture the high resolution image produced by the adaptive optics
Basic Functional Diagram
==> Figure
Seeing Infrared
==> In the infrared, the hardware of adaptive optics consists of an existing telescope, complete with its primary and secondary mirrors, and adds a separate box of optics, including the deformable mirror, to perform the atmospheric compensation
==> One is that each additional optical surface beam train absorbs some of the light from the target object in the sky, making the object appear fainter.
==> Also it emits light by virtue of its warmth, introducing thermal noise, further degrading the astronomers, ability to detect faint objects
What do we require?
==> Figure
Other Stars, Other Earths
==> Perhaps the most exciting scientific program to benefit from the new approach to adaptive optics will be to look at Jupiter like planets orbiting other stars.
==> Roughly 100 such stars have been found out through observations of the effects on the motion of their parent stars, but none has ever be seen by direct imaging.
==> It happens because they are extraordinarily faint and to compound the problem, they are right next to something that is enormously brighter
Conclusion
==> There are many substantial technological challenges in AO.
==> Among them are the development of fast, very low-noise detectors in order to be able to correct with fainter reference stars; high-power reliable & easy to operate sodium lasers; very fast processors exceeding 109 to 1010 operations per second; deformable mirrors with bandwidths of several kilohertz and with thousands of actuators, and large secondary adaptive mirrors.
==> The latter are especially interesting at thermal wavelengths, where any additional mirror raises the already huge thermal background seen by the instruments
References
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