Stability of the adaptive-optic point-spread function: Metrics, deconvolution, and initial Palomar results

The essential benefit of adaptive optics is delivering a telescope point-spread function (PSF) limited by diffraction rather than by atmospheric turbulence. In practice, achieving diffraction-limited PSF diameters is relatively routine for modern high-order systems, at least within a restricted isoplanatic patch containing the guide star. The lower-intensity wings of the PSF, though, are often highly complex in their structure and subject to variability over short time scales. Spurious bright knots can occur among the secondary Airy maxima, and the "waffle-mode" artifact may be problematic with a broad class of adaptive optics approaches. Good temporal stability of the adaptive-optic PSF is generally highly desirable if the full advantage of that spectacular PSF is to be realized; it is absolutely critical for many specific high-resolution programs that can only be attempted with adaptive optics. In the course of commissioning the high-order adaptive optics system built at JPL for the Palomar 200-inch telescope, we have investigated PSF stability in the field under a variety of conditions. We discuss here our experimental findings at Palomar, and their implications for some key scientific programs.