Adaptive optical system having automatic feedback aperture control

Claim 1

An adaptive optical system for controlling an optical beam conprising: wavefront adjusting means for controlling the wavefront of said beam; a variable aperture having a variable diameter for controlling the diameter of said beam; measurement and control means responsive to the optical beam power passing through said variable aperture for controlling said wavefront adjusting means, in which; said variable diameter is greater than the diameter of the Airy disk of said optical beam when said beam is initially switched on and said variable diameter is subsequently reduced to a diameter less than said Airy disk diameter, characterized in that: said variable aperture is formed by a fixed aperture having a diameter greater than said Airy disk, together with a filter medium disposed between said fixed aperture and said measurement means, said filter medium having the property that the transmissivity of said filter medium is a monotonic function of the intensity of optical radiation impinging thereon, whereby the effective diameter of said aperture automatically varies in size as the optical quality of said beam varies.