Shack–Hartmann wavefront sensor

Shack–Hartmann system in clinical optics: Laser creates a virtual light source in the retina. The lenslet array creates spots in the sensor according to the wavefront coming out of the eye.
Inverse of the Shack–Hartmann system in clinical optics: A set of patterns is displayed on the screen, the user aligns/overlaps them in a single image pressing buttons.
A schematic illustration of a SHWFS.
Operations of a single lenslet in a SHWFS.

A Shack–Hartmann (or Hartmann–Shack) wavefront sensor (SHWFS) is an optical detector used for measuring electromagnetic wavefronts. It is a wavefront sensor commonly used in adaptive optics systems and as a non-interferometric metrology tool. It consists of an array of lenses (called lenslets) of the same focal length. Each is focused onto a photon sensor (typically a CCD array or CMOS array or quad-cell). The SHWFS samples wavefronts using lenslet arrays to estimate centroids of the image formed referred to as a spot field. If the sensor is placed at the geometric focal plane of the lenslet, and is uniformly illuminated, then, the integrated gradient of the wavefront across the lenslet is proportional to the displacement of the centroid. Wavefronts that contain distortion are detected by the displacement of the spots on the spot field allowing for a complete reconstruction of the wavefront. SHWFS is unable to detect discontinuous steps in the wavefront since it is measuring distortion in a wavefront.

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