Wavefront Sensing of Extended sources

Abstract

Atmospheric turbulence is a major problem when imaging is done with the help of optical telescopes. Adaptive Optics has played a major role in compensating the turbulence to give a near diffraction-limited image. Our closest star, the Sun, is also affected by earth’s atmosphere turbulence. Since it is observed in day time, the spatial resolution is limited by seeing, largely compared to night time observation. Scene-based wave-front sensing (SBWFS) is a technique that allows an arbitrary scene to be used for wave-front sensing with adaptive optics (AO) instead of the normal point source. This makes AO feasible in a wide range of interesting scenarios. This report first presents the basic concepts and properties of SBWFS. Shack-Hartmann wavefront sensor is widely used for the measurement of phase perturbations induced by turbulence. Such a wavefront sensor relies on the measurement of the image displacements in the lenslet array focal plane. Different algorithms can be used to estimate this displacement. This report is dedicated to the correlation techniques which are well suited to extended sources. This technique results in lower noise than that of other centroiding algorithms.