Wave-front sensing for adaptive optics in astronomy

Since the invention of the telescope, astronomers have been able to view fainter and smaller objects in the sky. The main limitation to the quality of the images obtained has been, until recently, the presence of turbulence in the atmosphere. To mitigate the effects of the turbulence, adaptive optics systems have been successfully implemented. Adaptive optics relies upon measuring the distortion of the wave-front caused by the atmospheric turbulence, called wave-front sensing, and compensating for it in an adaptive fashion. The aim of this thesis is to provide a summary of the state-of-the-art of wave-front sensing and to describe my contributions to the field. The most significant result in the thesis is the derivation of a new wave-front sensing technique. This approach uses the geometric optics approximation, which considers light to travel perpendicular to the wave-front. Consequently, a wave-front slope in a region of the telescope aperture causes the displacement of a ray of light passing through that region. By taking two defocused images, it is possible todeduce how the light intensity changed from one image to the other.