Accounting for focal shift in the Shack-Hartmann wavefront sensor.

Alfredo Dubra // Publications // Sep 01 2019

PubMed ID: 31465350

Author(s): Akondi V, Dubra A. Accounting for focal shift in the Shack-Hartmann wavefront sensor. Opt Lett. 2019 Sep 1;44(17):4151-4154. doi: 10.1364/OL.44.004151. PMID 31465350

Journal: Optics Letters, Volume 44, Issue 17, Sep 2019

The Shack-Hartmann wavefront sensor samples a beam of light using an array of lenslets, each of which creates an image onto a pixelated sensor. These images translate from their nominal position by a distance proportional to the average wavefront slope over the corresponding lenslet. This principle fails in partially and/or non-uniformly illuminated lenslets when the lenslet array is focused to maximize peak intensity, leading to image centroid bias. Here, we show that this bias is due to the low Fresnel number of the lenslets, which shifts the diffraction focus away from the geometrical focus. We then demonstrate how the geometrical focus can be empirically found by minimizing the bias in partially illuminated lenslets.