Abstract

The Sun presents unusual problems for wavefront sensing. Unlike the nighttime sky, the Sun does not provide natural, high-contrast point sources, and creation of artificial beacons bright enough to be visible against the solar disk remains problematic with current technology. Small sunspots and pores can provide satisfactory substitutes for point sources, but these are available for only a tiny fraction of the solar disk. To measure wavefronts at arbitrary locations on the Sun, we must develop wavefront sensors capable of using the ubiquitous solar granulation as a target. Solar granulation is extended (its characteristic angular scale is about one arcsecond), unbounded (the angular extent of the composite pattern greatly exceeds the isoplanatic angle), low contrast (a few percent), and both spatially and temporally variable (the typical evolution time scale is minutes). A wavefront sensor must successfully contend with all these characteristics of solar granulation to be well-suited for general solar imaging.

© 1992 Optical Society of America