Nature Photonics 5, 21–23 (2011) doi:10.1038/nphoton.2010.297
Adaptive Imaging: MEMS Deformable Mirrors
Microelectromechanical systems (MEMS) technology has allowed the realization of cost-effective, high-performance deformable mirrors for adaptive-optics-enhanced imaging
The idea of using an array of actuators to change the shape of a mirror dates back to the second century AD, when Archimedes planned to destroy enemy ships using a solar heat ray. In his description, the shaped mirror was composed of an array of polished metal plates and the actuators were a group of Greek citizens who simultaneously aligned their mirrors such that the cumulative reflected sunlight converged to a common focal point on an enemy vessel, setting it aflame.
In modern times, more credible accounts of active light shaping date back to the invention of the eidophor projector in 1943 by Fritz Fischer, a scientist at the Swiss Federal Institute of Technology. The eidophor used electrostatic charge to locally deform an oil film on a mirror, thereby redirecting incident light for the earliest television projectors. It was this invention that inspired the astronomer Horace Babcock to dream up the concept of adaptive optics (AO), in which a dynamically reshaped mirror located in a plane conjugate to a telescope's primary mirror could be used to compensate for the blurring effects of the turbulent atmosphere between the telescope and the stars. The result, he predicted, would be a substantial increase in image resolution. The earliest deformable mirrors (DMs) developed to test Babcock's idea were made of metal-coated glass plates bonded to an underlying array of piezoelectric actuators. Although expensive and challenging to fabricate, these devices revolutionized astronomy by delivering Babcock's promise of increased telescopic resolution. By the early 1990s, such DMs and AO systems had proved invaluable in large ground-based telescopes.