Comparison of wavefront sensing with the Shack-Hartmann and pyramid sensors

The Shack-Hartmann wavefront sensor operates by subdividing the complex field in the aperture plane of the telescope with a lenslet array and forming low resolution images of the object. An alternative wavefront sensing scheme can be derived from placing a lenslet array at the focal plane of the aperture and forming low resolution images of the aperture. This arrangement can be viewed as the generalisation of the pyramid sensor and enables direct comparisons of the pyramid sensor with the Shack-Hartmann sensor. In particular, in this paper the performance of the reconstructor of the two sensors is investigated. Simulation results demonstrate that the lenslet array at the focal plane has equivalent performance to the Shack-Hartmann sensor in open loop when no modulation is applied to the lenslet array. However, when the array is modulated in a manner akin to the pyramid sensor, subdivision at the focal plane provides a significantly better wavefront estimate than the Shack-Hartmann sensor.

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