The acronym AOLI stands for “Adaptive Optics Lucky Imager”. This project aims at building a camera able to deliver diffraction limited images in the optical part of the spectrum. This instrument is designed for the 4.2-m William Herschel Telescope, in La Palma (Canary Islands), but is also built in the perspective of equipping in the future the 10.4-m Gran Telescopio de Canarias (GTC).
Obtaining optical diffraction limited images is very difficult to achieve from the ground considering. The atmospheric turbulence rapidly degrades the incoming wavefronts, which results in seeing-limited images with no spatial information below 0.8-1” resolution. Until a recent time, optical diffraction-limited images were only delivered by the HST, which operates in atmosphere-free conditions.
Since the original work of Antoine Labeyrie (1970) and David L. Fried (1978), it was shown that very short exposures of a source result into an irregular “speckled” image which characterize the instantaneous atmospheric turbulence. Several methods (e.g. the lucky imaging technique, the speckle interferometry and holography) have been developed to extract, under certain conditions, the high angular information from speckles data.
For long, “speckle science” has been scientifically limited to the observation of bright sources mainly because of read-out noise limitations of the detectors. As significant progress has been accomplished in the field of visible CCD detectors, in particular with EMCCD arrays, this has triggered a renaissance of the “fast imaging techniques”. This is what is exploited in AOLI.