ShackHartmann

Shack-Hartmann wavefront sensor is a device used to measure the shape of an incoming light wavefront. It is widely employed in optical metrology, adaptive optics, and vision science to assess wavefront distortions that affect image quality or focusing.

The principle relies on a microlens array that samples the wavefront into many subapertures. Each microlens focuses light from its subaperture onto a detector, typically a CCD or CMOS sensor. The detected spot positions, relative to a reference, correspond to the local tilt or slope of the wavefront across each subaperture. By recording these local slopes, a complete map of the wavefront distortion can be obtained.

Reconstruction of the wavefront phase from the measured slopes is performed with computational algorithms, such as least-squares, modal, or zonal methods. The resulting wavefront map identifies aberrations (e.g., defocus, astigmatism, coma) and can be used to drive corrective optics, such as a deformable mirror, in real time.

Applications of Shack-Hartmann sensors span several fields. In astronomy, they are central to adaptive optics systems that compensate atmospheric turbulence. In ophthalmology and vision science, they measure corneal and crystalline lens aberrations to aid diagnosis and custom corrective optics. They are also used for laser beam characterization, optical testing, and various research instrumentation.

Advantages include rapid, parallel measurement and suitability for dynamic wavefront changes. Limitations involve a finite dynamic range determined by spot displacement, sensitivity to noise and scattering, and the need for careful calibration of the microlens array and detector for accurate reconstruction. The method combines the Hartmann test concept with a microlens array and is named for its developers, Shack and Hartmann.