Astronomy

How does Adaptive Optics improve the performance of a telescope

adaptive optics telescope

This is how adaptive optics works. Light from a star passing through the atmosphere ends up as a distorted wavefront as the atmosphere is not static; the wave front changes every 5 to 10 milliseconds. An adaptive optics system has what is known as Shack-Hartmann WaveFront Sensor to analyse the light and sense the distortions. The system uses a point source of light as a reference beacon, whose light is used to find the shape of the waterfront. This could be a bright star or sodium vapors in the atmosphere, artificially illuminated by a laser beam from the ground.

The wave front sensor has a lenselet array that divides the light from a guide star into several parts, detects the brightness of each of these parts at high speed. The variations in the brightness are used to measure the distortions in the wavefront. The sensor then sends commands to actuators attached to a deformable mirror. The mirror is given equal but opposite distortions and the distorted wavelength is corrected upon reflection off the adjusted mirror.

The system must respond to wave front changes, while they are still small. The mirror’s shape should be updated about 100 to 200 times a second! Today’s computers and detectors make this order of rapid adjustments possible. Watch the animation below to understand how adaptive optics works.

Adaptive optics needs natural guide stars as near the objects of study stars near every celestial object. Hence another innovations solution has been found. At 95 cabooses the earth’s surface is a layer of sodium atoms that can be excited by a laser beam from the ground. It will create a point source that will serve as a guide star. The sodium atoms are left over by meteorite’s as they burn up in the atmosphere. The laser impact releases photons at 589 nm. This acts as a glowing spot in the sky. The light from the “artificial star “is from the celestial source may pass through a layer of atmosphere different from that of the laser guide star. These situations calls for more than just one artificial guide star.

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