Adaptive Optics for Extremely Large Telescopes 4 – Conference Proceedings

The time evolution of the sodium profile greatly impact the accuracy of laser guide star (LGS) wavefront sensor (WFS) measurements, for either the traditional thresholded center of gravity or the more advanced constraint matched filter/correlation algorithms. As a result, circularly symmetric wavefront aberrations will be induced in the adaptive optics (AO) corrected science wavefront for center launch LGS. In this paper, we describe our scheme to mitigate this issue by updating pixel processing parameters and employing a truth WFS during LGS AO operation. We also present simulation results using the sodium profiles measured by the UBC lidar. In addition, the time evolution of the turbulence profile will also have an impact on the pixel processing accuracy for the advanced algorithms, as well as the minimum variance wavefront reconstruction. We present simulation results showing how often we have to update the corresponding parameters to minimize the effect.