Photon counting versus CCD sensors for wavefront sensing: performance comparison in the presence of noise

Using simulations of time evolving speckle patterns we investigate the performance of three different wavefront sensors--a Shack-Hartmann sensor, a curvature sensor and an intensity moments based sensor. We compare the performance of these systems using detectors with two different levels of read noise--0 electronics read noise, corresponding to a photon counting detector and 5 electrons read noise, corresponding to a CCD. We also look at the effect of different source photon rates. For the UKIRT Upgrades program we will address the question which of the three wavefront sensors is optimal. We will also present a new simulation method for time-evolving speckle patterns using two turbulent layers.