The world’s most intense laser and the
largest terrestrial telescopes have one thing in common - they all employ
Adaptive Optics to achieve their superlative performance. So what is 'Adaptive
Optics'?
This technique corrects for optical distortions which would otherwise blunt
their capabilities. In the case of the Vulcan laser, sited at the Rutherford
Appleton Laboratory in the UK, Adaptive Optics, (AO) is used to
‘clean-up’ a beam degraded by thermal effects. This allows the
powerful laser pulses to be focussed down to generate almost unbelievable
intensities – 1,000,000,000,000,000,000,000 watts per square centimetre
– enough to explore the physics taking place inside stars.
For telescopes, the problem is again down to heating, but this time of the
atmosphere, which causes the well known twinkling of stars. In the past, this
phenomenon has severely limited the performance of terrestrial instruments.
However, all terrestrial telescopes currently being built or designed will
incorporate AO to provide images as sharp as those previously obtained only
from space.
Adaptive Optics is also finding applications on a more human scale - in eye
surgery to be exact. Here, like the atmosphere, the internal fluid is
constantly in motion, and a surgeon looking into a patient's eye gets a blurred
image of the retina. A new technique using AO is providing a much clearer
image, enabling improvements in eye surgery. It has even been suggested that,
in the longer term, AO could be used to endow people with supernormal vision!
BAE Systems have interests in many areas which could benefit from AO, including
laser and imaging systems. If, for example, a laser can be more efficiently
focussed onto a target, then a smaller device can be used, leading to size,
energy and cost savings. Such improvements need not be dramatic to be
worthwhile, and BAE Systems' strategy is to develop AO systems which are
compact and relatively inexpensive, but which nevertheless provide a useful
improvement in performance. We are actively engaged in developing all aspects
of practical AO systems, and recent test-bed results have been successful.
Deformable mirrors and their control is one of the areas being tackled by our
experts at the ATC. These employ an array of small devices that push and pull a
glass or polished metal surface into the required shape. Our latest design has
a gold coated mirror approximately 90 mm in diameter which can be reshaped up
to 1000 times every second in order to correct for even the fastest movement of
the atmosphere.
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Gold coated deformable mirror developed at ATC
All AO systems consist of three main parts: a wavefront sensor to measure the
optical distortion, a deformable mirror which corrects for this distortion, and
a control system which links the two.
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