Adaptive optics

Adaptive optics (AO) is a technique of precisely deforming a mirror in order to compensate for light distortion.

Adaptive optics works by measuring the distortions in a wavefront and compensating for them with a device that corrects those errors such as a deformable mirror or a liquid crystal array.

Adaptive optics was first envisioned by Horace W. Babcock in 1953,[6][7] and was also considered in science fiction, as in Poul Anderson's novel Tau Zero (1970), but it did not come into common usage until advances in computer technology during the 1990s made the technique practical.

Some of the initial development work on adaptive optics was done by the US military during the Cold War and was intended for use in tracking Soviet satellites.

[8] Microelectromechanical systems (MEMS) deformable mirrors and magnetics concept deformable mirrors are currently the most widely used technology in wavefront shaping applications for adaptive optics given their versatility, stroke, maturity of technology, and the high-resolution wavefront correction that they afford.

In order to perform adaptive optics correction, the shape of the incoming wavefronts must be measured as a function of position in the telescope aperture plane.

A technique known as "multiconjugate adaptive optics" uses several deformable mirrors to achieve a greater field of view.

Rayleigh guide stars work by propagating a laser, usually at near ultraviolet wavelengths, and detecting the backscatter from air at altitudes between 15 and 25 km (49,000 and 82,000 ft).

These optical aberrations diminish the quality of the image formed on the retina, sometimes necessitating the wearing of spectacles or contact lenses.

In the case of retinal imaging, light passing out of the eye carries similar wavefront distortions, leading to an inability to resolve the microscopic structure (cells and capillaries) of the retina.

Spectacles and contact lenses correct "low-order aberrations", such as defocus and astigmatism, which tend to be stable in humans for long periods of time (months or years).

While correction of these is sufficient for normal visual functioning, it is generally insufficient to achieve microscopic resolution.

It is also expected to play a military role by allowing ground-based and airborne laser weapons to reach and destroy targets at a distance including satellites in orbit.

[23] Adaptive and active optics are also being developed for use in glasses to achieve better than 20/20 vision, initially for military applications.

In material processing using lasers, adjustments can be made on the fly to allow for variation of focus-depth during piercing for changes in focal length across the working surface.

[25] This eliminates the need for optic of the laser head to be switched, cutting down on overall processing time for more dynamic modifications.

A rather simple example is the stabilization of the position and direction of laser beam between modules in a large free space optical communication system.