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Improved iteratively weighted centroiding for accurate spot detection in laser guide star based Shack Hartmann sensor

A hybrid centroiding technique involving Iteratively Weighted Center of Gravity (IWCoG) algorithm and correlation technique for a Laser Guide Star (LGS) based Shack Hartmann wavefront sensor is proposed. A simple method for simulating LGS elongated spots with photon noise and read out noise is demonstrated. The problems associated with IWCoG are addressed (a) Error saturation is minimized by adding random numbers iteratively to centroid positions, (b) non uniform convergence of Centroid Estimation Error (CEE) is reduced by using the hypothesis that the iteration number with maximum correlation between the weighting function and the actual spot image function is the iteration with minimum error, (c) convergence rate is improved by shifting the weighting function to the point of maximum intensity in first iteration. The novelty of the algorithm is tested by comparing with other centroiding algorithms.