Abstract

The feasibility of using adaptive optics (AO) systems on large ground based optical telescopes for producing compensated images of both astronomical sources and artificial earth satellites has been demonstrated by a number of research groups. AO systems consist conceptually of a wavefront sensor (WFS) which measures atmospherically induced wavefront phase perturbations faster than the rate at which they occur and a wavefront phase compensation device, typically a deformable mirror, which takes the WFS data and produces a conjugate phase correction nulling the distortion. In the case of faint sources, the ability of an AO system to produce phase corrections is limited by the signal-to-noise ratio (SNR) in the WFS. In the case of the Shack Hartmann (SH) WFS this limit is a function of the SNR required to estimate with sufficient accuracy the centroid positions of unresolved images of the source formed by a lenslet array on an array of quadrant detectors composing the subapertures of the WFS. Although the use of laser guidestars may allow the substitution of faint source radiation with a bright artificial AO beacon, considerations of cost and complexity motivate a continuing interest in improving the detection sensitivity of a source referenced, low light level (LLL) WFS. This paper explores the promise of aluminum gallium arsenide/gallium arsenide (AlGaAs/GaAs) heterostructure photocathodes coupled to shot noise limited photon counting (PC) cameras and compares their performance with the read noise limited charge coupled device (CCD) cameras often used in this application. Figure (1) illustrates the quantum efficiency of the various detectors to be considered in the study, including two high performance AlGaAs/GaAs photocathodes recently obtained from Litton Electro-Optical Systems.

© 1996 Optical Society of America