Wavefront reconstruction with the adaptive Shack-Hartmann sensor

In a Shack-Hartmann sensor the wavefront to be measured is sampled by a microlens array. The beams are directed to a spot in the focal plane. The displacement of the spots is a measure for the local gradient of the wavefront over one microlens. In the adaptive Shack-Hartmann sensor the static microlens array of the conventional sensor is replaced by a dynamic liquid crystal display (LCD). The LCD is used to display an array of Fresnel microlenses. Thereby, the Fresnel microlenses can be adapted to the wavefront and the design parameters like focal length, aperture size, position and number of lenses can be changed very quickly. We present an investigation about the wavefront reconstruction with the adaptive Shack-Hartmann sensor. Because of the large pixelsize of the LCD in comparison to static manufactured holograms the microlens diameter of the adaptive Shack-Hartmann sensor is larger than in a conventional sensor. This requires considerations in the reconstruction algorithm to minimize reconstruction errors. We compare Zernike and B-Spline wavefront reconstruction on the basis of fit accuracy, reconstruction time and the effect of missing measurement data and noise. We come to the conclusion that Zernike reconstruction is better for fitting simple wavefronts while B-Spline reconstruction is the better choice for more complex wavefronts.