ShackHartmannWellenfrontsensor

The Shack-Hartmann wavefront sensor (SHWS) is an optical instrument used to measure the shape of a light wavefront by sampling it with a microlens array and recording the resulting spot pattern on a detector. If the incoming wavefront is planar, each lenslet focuses light to a spot near the optical axis; if the wavefront is distorted, spots are displaced. The array of spot displacements provides local slope measurements of the wavefront across the pupil.

A typical SHWS comprises a lenslet array, a imaging detector (such as a CCD or CMOS camera), and relay optics that form an image of the lenslet focal plane on the detector. The positions of the spots are determined by centroiding or peak finding. From the measured local slopes, the wavefront phase can be reconstructed using methods such as zonal reconstruction, modal decomposition (for example into Zernike polynomials), or least-squares optimization.

Shack-Hartmann sensors are widely used in adaptive optics to compensate atmospheric or other aberrations in real time, in optical testing to characterize beam quality, and in ophthalmology for corneal and ocular aberration measurements. They offer direct, parallel sampling of the wavefront and good dynamic range, though accuracy depends on lenslet sampling, detector noise, and calibration. Limitations can include spot overlap at high orders, sensitivity to scintillation, and the need for robust algorithms to handle missing or noisy spot measurements. Overall, the SHWS provides a practical balance of speed, resolution, and reliability for measuring complex wavefront distortions.