Noise reduction in the centroiding of laser guide star spot pattern using thresholded Zernike reconstructor

Abstract

Centroiding inaccuracies contribute to most of the wavefront reconstruction error in a Shack Hartmann sensor based adaptive optics system. These errors primarily occur due to the presence of photon noise, readout noise, finite background and strong scintillations. Elongation of the spots in the case of large apertures while using Laser guide star as reference makes the situation further worse. A denoising procedure based on thresholded Zernike reconstructor and pattern matching is suggested in this paper to largely overcome these problems. Individual spot pattern images are reconstructed using Zernike polynomials and matched with ideal spot pattern without distortion to arrive at accurate local centroid positions.