As members of the Center for Adaptive Optics (CfAO) we use the adaptive optics systems at the Lick and Keck observatories. Turbulence in our atmosphere limits the seeing of telecopes to approximately 1 arcsecond, while the diffraction limit of a telescope is approximately equal to the ratio of the wavelength and the diameter of the mirror. One can increase the angular resolution in the following ways:

1) Go up into space; The primary reason for the Hubble Space Telescope (HST) was to get above the atmosphere so sharper images could be obtained.

2) Speckle imaging:During a short (100-200 msec) exposure the atmosphere is `frozen' and the diffraction limit of the telescope is reached. By combining hundreds of images, properly shifted (or using FFT algorithms), one can build up a high resolution image of the object (see "Infrared Observations" page).

3) Adaptive Optics: By using a deformable mirror and a wavefront sensor, the distortions in the incoming wavefront, as caused by atmospheric turbulence, can be corrected so that one can obtain a diffraction limited image of the object of interest. If your object is small (less than a few arcseconds across) and bright, it can serve as its own guidestar. For weaker and extended sources one needs to find a guidestar nearby (within 30 arcseconds at Keck), or use an artificial star, e.g., resulting from a laser beacon. The graph shows the basics of an adaptive optics system (Courtesy: Wolfgang Hackenberg and Andreas Quirrenbach).