Wavefront correction through image sharpness maximisation

A key component of any adaptive optics system (AO) for the correction of wavefront aberrations, is the wavefront sensor (WFS). Many systems operate in a mode where a WFS measures the aberrations present in the incoming beam. The required corrections are determined and applied by the wavefront corrector- often a deformable mirror (DM). We wish to develop a wavefront sensor-less correcting system, as derived from the original adaptive optics system of Muller and Buffington[1]. In this experiment we employ a method in which a correcting element with adjustable segments is driven to maximise some function of the image. We employ search algorithms to find the optimal combination of actuator voltages to maximise a certain sharpness metric. The “sharpness ” is based on intensity measurements taken with a CCD camera. Results have been achieved using a Nelder-Mead variation of the Simplex algorithm[2]. Preliminary results show that the Simplex algorithm can minimise the aberrations and restore the Airy rings of the imaged point source. Good correction is achieved within 50-100 iterations of the Simplex algorithm. The results are repeatable and so-called “blind ” correction of the aberrations is achieved. The correction achieved using various sharpness algorithms laid out by Muller and Buffington are evaluated and presented