| Because atmospheric turbulence causes distortions in stellar wavefronts, passive ground based telescopes, no matter how large, are limited to the resolution limit of a 0.1-0.2m aperture when imaging in the visible. If the new class of large aperture (10 m) telescopes is to reach its resolution potential, adaptive optics must be employed to compensate for the atmospheric wavefront distortions. Vital to an adaptive optics system is the ability to accurately sense the distorted wavefront. Two new methods for wavefront sensing show great promise for the field of adaptive optics. A reflective hybrid of the traditional Shack-Hartmann wavefront sensor has produced near diffraction limited imaging with the Multiple Mirror Telescope, a hexagonal array of six, 1.83 m mirrors. It is also directly applicable to filled aperture telescopes. Another wavefront sensor, the stellar phase shifting interferometer, has produced for the first time ever direct phase map measurements of atmospherically distorted wavefronts. The ability to directly measure the phase of the wavefront at each detector pixel paves the way for a new generation of light efficient and accurate wavefront sensors for adaptive optics. |
