Calibration of wavefront sensors without knowledge of the reference wavefront

Wavefront quality is a critical parameter for many applications. For absolute wavefront measurements the systematic sensor error of the measurement device has to be known. While a calibration is typically performed by using a reference wavefront which is assumed to be known, we present a calibration scheme where knowledge of the reference wavefront is not required. Here, the sensor is moved stepwise perpendicular to an expanded reference wavefront. As the relative tilt angles between sensor and wavefront at each position are measured simultaneously a reconstruction of the sensor error and the shape of the reference beam including defocus and astigmatism can be performed. For validation of the calibration scheme a temperature stabilized Shack Hartmann sensor is used. Various optical elements were inserted into the setup to introduce wave front aberrations to the reference beam or additional sensor errors to the detector. Even for strongly disturbed reference waves with aberrations in the order of a micrometer the determined sensor errors deviates no more than 7 nm (PV) from the mean sensor error corresponding to lambda/75