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Simple and robust algorithm to extend the dynamic range of tip-tilt for a Shack-Hartmann sensor.

We propose an algorithm to extend the dynamic range of tip-tilt (TT) for a Shack-Hartmann wave-front sensor. With this method, the dynamic range of TT is determined by the size of the whole CCD pixel array rather than the size of the sub-aperture. Thus the separate TT sensor in adaptive optics (AO) systems for optical telescope can be saved, which will simplify the systems and enhance the light energy efficiency. The proposed algorithm is computationally effective and appropriate for the real-time TT computation of AO systems. The simulated and experimental results show that the algorithm is robust to realistic scintillation and photon noise and can work well under poor observing conditions. For the given condition with r0 of 5 cm at 550 nm and average flux of 100 photons per sub-aperture, the ultimate measurement accuracy of TT is about 5% pixels (peak-to-valley value).