Adaptive optics for diffraction-limited infrared imaging with 8-m telescopes

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Abstract
When equipped with adaptive optics, the coming generation of large 6–10-m telescopes can combine huge light grasp with very sharp images. We describe a specific design concept for recovery of diffraction-limited images in the 1.6- and the 2.2-μm atmospheric windows, yielding 0.05-arcsec resolution for an 8-m telescope. Our goal has been to achieve this performance routinely by not requiring above-average atmospheric conditions or the use of unusually bright nearby stars. Atmospheric blurring is sensed with a sodium laser beacon of a few watts. Image motion is sensed by starlight, with a quadrant detector that is sensitive to the broad infrared band in which photon flux is typically largest and the field star has been sharpened by laser-beacon correction that is shared with the science target. A detailed performance analysis shows that for typical conditions Strehl ratios of <25% are expected at 2.2 μm, with the probability of finding a sufficiently bright field star exceeding 50%.