Talbot- versus Shack-Hartmann Sensor: global aberration measurement in the presence of mid-frequency waviness

Wave front sensors are applied in the measurement of the wave aberrations of the human eye. Such measurements have to guarantee a very high degree of safety being the basis for ablative corrections with the excimer laser. PMMA-platelets with an ablated surface profile are a possible material for a calibration retarder. Due to the point-like ablation process the resulting retarder shows a certain amount of mid-frequency waviness aggravating the measurement of global aberrations. It will be shown how this type of waviness hampers the performance of the Talbot and the Shack-Hartmann sensor. Fizeau-interferograms are used as a back-up.