Shack–Hartmann wavefront sensor with enhanced dynamic range and reference-free operation

We present a method for increasing the dynamic range of a Shack–Hartmann wavefront sensor with a hexagonal lenslet array. Increasing the dynamic range is equivalent to calculating the spot displacement correctly, when it is bigger than the subaperture radius. Our method does this by sorting and indexing the spots according to centered hexagonal number. This allows tracking of the wandering of each spot separately. Further, we also show that the system can work in a reference-free mode if we are not interested in the tip and tilt terms. The results of the work are presented along with the details of the algorithm and theory.