Telescopes on the ground must observe objects in deep space through the interference of the earth's atmosphere. As light passes through the atmosphere it gets spread out by turbulence due to wind shear and changes in temperature and pressure within the atmospheric layers. These effects reduce the resolving power of earth-based telescopes, spreading a stellar point-source image into a resolvable "seeing" disk. This difficulty can be overcome to a large extent by monitoring a bright star near the object of interest and looking for the rapidly varying distortions and displacements of the reference star's image that are introduced as its light passes through the atmosphere. These "guide star" signals are fed into an Adaptive Optics (AO) system that uses a "wavefront sensor" and a "deformable mirror" to restore the image to (nearly) what would be seen from above the atmosphere.
These techniques have been with us for some time and are now becoming mature and routine, especially on larger telescopes where the diffraction limit is much smaller than the typical seeing disk. Dr. Olivier Guyon of the University of Arizona is developing a more complex and sophisticated approach to wavefront sensing that promises to deliver higher sensitivity plus a greatly improved ability to separate nearby objects, especially when one of them is much brighter than the other. This is very important for finding faint planets next to their stars. Currently most wavefront sensing is done using a linear approximation. Dr. Guyon will deliver a non-linear curvature wavefront sensing capability that he expects will enhance the contrast by a factor of 50 to 100 over current methods. Dr. Guyon's work is funded by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.
