Image reconstruction by means of wave-front sensor measurements in closed-loop adaptive-optics systems

Abstract

Theoretical and experimental investigations of the imaging technique referred to as speckle holography have shown that wave-front information can be used in the postprocessing of astronomical data to improve the quality of images. In a closed-loop adaptive-optics system the wave-front sensor is continuously measuring the residual wave-front error. Thus wave-front information is continuously available for use in image reconstruction. We show here that wave-front information in a closed-loop adaptive-optics system, used in a postprocessing scheme, can improve the phase of the compensated optical-transfer function in systems with finite delays between wave-front sensing and phase correction. This technique is closely related to speckle holography and is referred to here as compensated speckle holography. This method requires good spatial sampling of the residual phase error and degrades gracefully as the wave-front sensor signal-to-noise ratio decreases. Also, the technique can be used to reduce the required closed-loop bandwidth of an imaging system, permitting longer integration times in the wave-front sensor, and thus allowing dimmer objects to be imaged without the use of an artificial guide star.