wavefront sensor

A wavefront sensor is an instrument for determining an EMR wave's deformation, used to control a correcting instrument in an adaptive optics (AO) system. Types include:

• Shack-Hartmann sensor - focuses spots and senses their position.
• wavefront curvature sensor - focuses spots and measures relative intensity.
• pyramid sensor - splits image four ways, each from a quarter of the aperture, so their positions can be compared.

The deformation of interest consists of the wave lacking coherence of its phase, i.e., over a cross-section of the passing EMR, some has its wave peak passing earlier and some later. If the EMR is collimated, the deformation consists of it being something other than a plane wave, and if it is focused to or from a point, the problem consists of the wave's peak varying in its distance from the focal point.